Similar to other cropping systems, few walnut cultivars are used as scion in commercial production. Germplasm collections can be used to diversify cultivar options and hold potential for improving crop productivity, disease resistance and stress tolerance. In this study we explored the anatomical and biochemical bases of photosynthetic capacity in 11 J. regia accessions in the USDA-ARS National Clonal Germplasm Repository. Net assimilation rate (An) differed significantly among accessions and was greater in those from lower latitudes coincident with increases in stomatal and mesophyll conductance, leaf thickness, mesophyll porosity and gas-phase diffusion, and leaf nitrogen, and lower leaf mass and stomatal density. High CO2-saturated assimilation rates led to increases in An under limiting conditions. Greater An was found in lower latitude accessions native to climates with more frost-free days, greater precipitation seasonality, and lower temperature seasonality. As expected, water stress consistently impaired photosynthesis with the highest % reductions in three lower latitude accessions (A3, A5, and A9), which had the highest An under well-watered conditions. However, An for A3 and A5 remained amongst the highest under dehydration. J. regia accessions, which have leaf structural traits and biochemistry that enhance photosynthesis, could be used as commercial scions or breeding parents to enhance productivity.

How variations in carbon supply affect wood formation remains poorly understood in particular in mature forest trees. To elucidate how carbon supply affects carbon allocation and wood formation, we attempted to manipulate carbon supply to the cambial region by phloem girdling and compression during the mid- and late-growing season and measured effects on structural development, CO2 efflux, and nonstructural carbon reserves in stems of mature white pines. Wood formation and stem CO2 efflux varied with location relative to treatment (i.e., above or below the restriction). We observed up to twice as many tracheids formed above versus below the treatment after the phloem transport manipulation, whereas cell-wall area decreased only slightly below the treatments, and cell size did not change relative to the control. Nonstructural carbon reserves in the xylem, needles, and roots were largely unaffected by the treatments. Our results suggest that low and high carbon supply affects wood formation, primarily through a strong effect on cell proliferation, and respiration, but local nonstructural carbon concentrations appear to be maintained homeostatically. This contrasts with reports of a decoupling of source activity and wood formation at the whole-tree or ecosystem level, highlighting the need to better understand organ-specific responses, within-tree feedbacks, as well as phenological and ontological effects on sink-source dynamics.

While many phenylpropanoid pathway-derived molecules act as physical and chemical barriers to pests and pathogens, comparatively little is known about their role in regulating plant immunity. To explore this research field, we transiently perturbed the phenylpropanoid pathway through application of the CINNAMIC ACID-4-HYDROXYLASE (C4H) inhibitor piperonylic acid (PA). Using bioassays involving diverse pests and pathogens, we show that transient C4H inhibition triggers systemic, broad-spectrum resistance in higher plant without affecting growth. PA treatment enhances tomato (Solanum lycopersicum) resistance in field and laboratory conditions, thereby illustrating the potential of phenylpropanoid pathway perturbation in crop protection. At the molecular level, transcriptome and metabolome analyses reveal that transient C4H inhibition in tomato reprograms phenylpropanoid and flavonoid metabolism, systemically induces immune signaling and pathogenesis-related genes, and locally affects reactive oxygen species metabolism. Furthermore, C4H inhibition primes cell wall modification and phenolic compound accumulation in response to root-knot nematode infection. Although PA treatment induces local accumulation of the phytohormone salicylic acid, the PA resistance phenotype is preserved in tomato plants expressing the salicylic acid-degrading NahG construct. Together, our results demonstrate that transient phenylpropanoid pathway perturbation is a conserved inducer of plant resistance and thus highlight the crucial regulatory role of this pathway in plant immunity.

Iron (Fe) deficiency restricts crop yields in calcareous soil. Thus, a novel Fe chelator, proline-2′-deoxymugineic acid (PDMA), based on the natural phytosiderophore 2′-deoxymugineic acid (DMA), was developed to solve the Fe deficiency problem. However, the effects and mechanisms of PDMA relevant to the Fe nutrition and yield of dicots grown under field conditions require further exploration. In this study, pot and field experiments with calcareous soil were conducted to investigate the effects of PDMA on the Fe nutrition and yield of peanuts. The results demonstrate that PDMA could dissolve insoluble Fe in the rhizosphere and up-regulate expression of the yellow stripe-like family gene AhYSL1 to improve the Fe nutrition of peanuts. Moreover, the chlorosis and growth inhibition induced by Fe deficiency were significantly diminished. Importantly, under field conditions, the peanut yield and kernel micronutrition were notably promoted by PDMA application. Our results indicate that PDMA promotes the dissolution of insoluble Fe and a rich supply of Fe in the rhizosphere, increasing yields through integrated improvements in soil–plant Fe nutrition at the molecular and ecological levels. In conclusion, the efficacy of PDMA for improving the Fe nutrition and yield of peanut indicates its outstanding potential for agricultural applications.

Since the first description of phloem sap composition nearly 60 years ago, it is generally assumed that phloem sap does not contain nitrate and that there is little or no backflow of nitrate from shoots to roots. While it is true that nitrate can occasionally be absent from phloem sap, there is now substantial evidence that phloem can carry nitrate and furthermore, transporters involved in nitrate redistribution to shoot sink organs and roots have been found. This raises the question of why nitrate may or may not be present in phloem sap, why its concentration is generally kept low, and whether plant shoot-root nutrient cycling also involves nitrate. We propose here that phloem sap nitrate is not only an essential component of plant nutritional signaling but also contributes to physical properties of phloem sap and as such, its concentration is controlled to ensure proper coordination of plant development and nutrient transport.

The Antarctic green alga Chlamydomonas sp. UWO241 is an obligate psychrophile that thrives in the cold (4-6°C) but is unable to survive at temperatures ≥18°C. Little is known how exposure to heat affects its physiology or whether it mounts a heat stress response in a manner comparable to mesophiles. Here, we dissect the responses of UWO241 to temperature stress by examining its growth, primary metabolome and transcriptome under steady-state low temperature and heat stress conditions. In comparison with Chlamydomonas reinhardtii, UWO241 constitutively accumulates metabolites and proteins commonly considered as stress markers, including soluble sugars, antioxidants, polyamines, and heat shock proteins to ensure efficient protein folding at low temperatures. We propose that this permanent stress metabolism is an adaptive advantage to life at extreme conditions. A shift from 4°C to a non-permissive temperature of 24°C alters the UWO241 primary metabolome and transcriptome, but growth of UWO241 at higher permissive temperatures (10°C and 15°C) does not provide enhanced heat protection. UWO241 also fails to induce the accumulation of HSPs when exposed to heat, suggesting that it has lost the ability to fine-tune its heat stress response. Our work adds to the growing body of research on temperature stress in psychrophiles, many of which are threatened by climate change.

With continued global warming, plants are forecast to increasingly experience abiotic stress(es). Stomata on leaf surfaces are the gatekeepers to plant interiors, regulating gaseous exchanges that are crucial for both photosynthesis and outward water release. To optimise future productivity, accurate modelling of how stomata govern plant-environment interactions will be crucial. Here, we synergise optical and thermal imaging data to enhance transpiration modelling during water and/or nitrogen stress. By utilising hyperspectral data and partial least squares regression analysis of six plant traits and fluxes in wheat ( Triticum aestivum), we have developed a new spectral vegetation index; the combined nitrogen and drought index (CNDI), which can be used to detect both water stress and/or nitrogen deficiency. Upon full stomatal closure during drought, CNDI reduces as leaf biochemistry changes unfold, and during a combined stress experiment (drought and nitrogen deficiency), this is reflected in CNDI showing a strong relationship with leaf relative water content ( r2 = 0.70). By incorporating CNDI transformed with a sigmoid function into thermal-based transpiration modelling, we have increased the accuracy of modelling water fluxes during abiotic stress. If employed using future remote sensing technologies, our findings have the potential to markedly improve agricultural water usage and yields.

CONSTANS-LIKE (COL) family members are commonly implicated in light signal transduction during early photomorphogenesis. However, some of their functions remain unclear. Here, we propose a role for COL13 in hypocotyl elongation in Arabidopsis thaliana. We found that COL13 RNA accumulates at high levels in hypocotyls and that a disruption in the COL13 function via a T-DNA insertion or RNAi led to the formation of longer hypocotyls of Arabidopsis seedlings under red light. On the contrary, overexpression of COL13 resulted in the formation of shorter hypocotyls. Using various genetic, genomic, and biochemical assays, we proved that another COL protein, COL3, directly binds to the promoter of COL13, and the promoter region of COL3 was targeted by the transcription factor LONG HYPOCOTYL 5 (HY5), to form an HY5-COL3-COL13 regulatory chain for regulating hypocotyl elongation under red light. Additionally, further study demonstrated that COL13 interacts with COL3, and COL13 promotes the interaction between COL3 and CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1), suggesting a possible COP1-dependent COL3-COL13 feedback pathway. Our results provide new information regarding the gene network in mediating hypocotyl elongation.

Opportunistic diversification has allowed ferns to radiate into epiphytic niches in angiosperm dominated landscapes. However, our understanding of how ecophysiological function allowed establishment in the canopy and the potential transitionary role of the hemi-epiphytic life form remain unclear. Here, we surveyed 39 fern species in Costa Rican tropical forests to explore epiphytic trait divergence in a phylogenetic context. We examined leaf responses to water deficits in terrestrial, hemi-epiphytic, and epiphytic ferns and related these findings to functional traits that regulate leaf water status. Epiphytic ferns had reduced xylem area (-63%), shorter stipe lengths (-56%), thicker laminae (+41%), and reduced stomatal density (-46%) compared to terrestrial ferns. Epiphytic ferns exhibited similar turgor loss points, higher osmotic potential at saturation, and lower tissue capacitance after turgor loss than terrestrial ferns. Overall, hemi-epiphytic ferns exhibited traits that share characteristics of both terrestrial and epiphytic species. Our findings clearly demonstrate the prevalence of water conservatism in both epiphytic and hemi-epiphytic ferns, via selection for anatomical and structural traits that avoid leaf water stress. Even with likely canalized physiological function, adaptations for drought avoidance have allowed epiphytic ferns to successfully endure the stresses of the canopy habitat.

Known elicitors of plant defenses against eggs of herbivorous insects are low-molecular-weight organic compounds associated with the eggs. However, previous studies provided evidence that also proteinaceous compounds present in secretion associated with eggs of the herbivorous sawfly Diprion pini can elicit defensive responses in Pinus sylvestris. Pine responses induced by the proteinaceous secretion are known to result in enhanced emission of (E)-β-farnesene, which attracts egg parasitoids killing the eggs. Here, we aimed to identify the defense-eliciting protein and elucidate its function. After isolating the defense-eliciting protein from D. pini egg secretion by ultrafiltration and gel electrophoresis, we identified it by MALDI-ToF mass spectrometry as an annexin-like protein, which we named “diprionin”. Further GC-MS analyses showed that pine needles treated with heterologously expressed diprionin released enhanced quantities of (E)-β-farnesene. Our bioassays confirmed attractiveness of diprionin-treated pine to egg parasitoids. Expression of several pine candidate genes involved in terpene biosynthesis and regulation of ROS homeostasis was similarly affected by diprionin and natural sawfly egg deposition. However, the two treatments had different effects on expression of pathogenesis related genes (PR1, PR5). Diprionin is the first egg-associated proteinaceous elicitor of indirect plant defense against insect eggs described so far.

Tropical forests are experiencing unprecedented high temperature conditions due to climate change that could limit their photosynthetic functions. We studied the high temperature sensitivity of photosynthesis in a rainforest site in southern Amazonia, where some of the highest temperatures and most rapid warming in the Tropics have been recorded. The quantum yield (Fv/Fm) of photosystem II was measured in seven dominant tree species using leaf discs exposed to varying levels of heat stress. T50 was calculated as the temperature at which Fv/Fm) was half the maximum value. T5 is defined as the breakpoint temperature, at which Fv/Fm) decline was initiated. Leaf thermotolerance in the rapidly warming Southern Amazonia was the highest recorded for forest tree species globally. T50 and T5 varied between species, with one mid storey species, Amaioua guianensis, exhibiting particularly high T50 and T5 values. While the T50 values of the species sampled were several degrees above the maximum air temperatures experienced in southern Amazonia, the T5 values of several species are now exceeded under present-day maximum air temperatures.

We explored the effects, on photosynthesis in cowpea (Vigna unguiculata), of high temperature and light — environmental stresses that often co-occur under field conditions. We observed contrasting responses in the light and carbon assimilatory reactions, whereby in high temperature, the light reactions were stimulated while CO2 assimilation was substantially reduced. There were two striking observations. First, the primary quinone acceptor (QA), a measure of the regulatory balance of the light reactions, became more oxidized with increasing temperature, suggesting increased electron sink capacity, despite the reduced CO2 fixation. Second, a strong, O2-dependent inactivation of assimilation capacity, consistent with down-regulation of rubisco under these conditions, a phenomenon that has not been previously reported. The dependence of these effects on CO2, O2 and light led us to conclude that both photorespiration and an alternative electron acceptor, supported increased electron flow, and thus provided photoprotection, under these conditions. Further experiments showed that the increased electron flow was maintained by rapid rates of PSII repair, particularly at combined high light and temperature. Overall, the results suggest that photodamage to the light reactions can be avoided under high light and temperatures by increasing electron sink strength, even when assimilation is strongly suppressed.

Breeding drought stress tolerance is an integral part of our current and future goals of sustainable agricultural production. In the present study, we examined the natural variation of HvP5cs1 and demonstrated the utility of a wild barley allele for drought stress adaptation in cultivated barley. Sequencing the 5-end regulatory region among 49 barley accessions identified a genetically distinct allele of HvP5cs1 promoter from a wild barley ISR42-8. Allele mining of HvP5cs1 indicated quantitative variation in proline accumulation which was associated with promoter polymorphisms across the cluster of abscisic acid-responsive elements (ABRE), ABRE-related coupling elements, and MYB binding motifs. A near-isogenic line (NIL-143) harboring the HvP5cs1 allele from the highest proline accumulating wild barley ISR42-8 was developed in cultivated barley Scarlett through marker-assisted backcrossing (BC6). NIL-143 preserved the genetic competence of ISR42-8 to accumulate proline in higher concentrations under drought conditions at seedling and reproductive stages. Under drought stress, NIL-143 maintained superior membrane integrity, reduced pigment damage, and sustained photosynthetic health compared to Scarlett. NIL-143 presented a remarkable improvement in drought stress recovery than Scarlett. Further, the introgression line exhibited improved yield attributes, especially superior grain weight compared to Scarlett under field drought conditions. In conclusion, the present data uncover the genetic regulation of HvP5cs1 mediated proline accumulation and elucidate its role in drought stress adaptation and yield stability in barley.

Species interactions and mechanisms affect plant coexistence and community assembly. Despite increasing knowledge of kin recognition and allelopathy in regulating interspecific and intraspecific interactions among plants, little is known about whether kin recognition mediates allelopathic interference. We used allelopathic rice cultivars with the ability for kin recognition grown in kin vs. non-kin mixtures to determine their impacts on paddy weeds in field trials and a series of controlled experiments. We experimentally tested potential mechanisms of the interaction via altered root behavior, allelochemical production, and soil microbial community composition, as well as carbon and nitrogen partitioning in the weeds. We consistently found that the establishment and growth of paddy weeds were more inhibited by kin mixtures compared to non-kin mixtures. The effect was driven by kin recognition that induced altered root placement, established similar soil microbial communities, and altered weed carbon and nitrogen partitioning. Importantly, genetic relatedness enhanced the production of intrusive roots towards weeds and reduced the production of rice allelochemicals. These findings suggest that relatedness allows allelopathic plants to discriminate their neighboring collaborators (kin) or competitors and then adjust their growth, competitiveness and chemical defense accordingly.

Microbe associated molecular pattern (MAMP) triggered immunity research has traditionally centred around signal transduction pathways originating from activated membrane localised pattern recognition receptors (PRRs), culminating in nuclear transcription and post translational modifications. More recently, chloroplasts have emerged as key immune signalling hubs. Chloroplasts play a central role in integrating environmental signals. Notably MAMP recognition induces chloroplastic ROS (cROS) which is suppressed by pathogens effectors, which also modify the balance of defence hormone precursors, jasmonic acid (JA), salicylic acid (SA) and abscisic acid (ABA), whose precursors are chloroplast synthesised. This study focuses on how well characterised PRRs and co-receptors modulate chloroplast physiology, examining whether diverse signalling pathways converge to similarly modulate chloroplast function. Pre-treatment of receptor mutant plants with MAMP and D(Damage)AMP peptides usually protect against effector modulation of chlorophyll fluorescence and prevent Pseudomonas syringae effector mediated quenching of cROS and suppression of Fv/Fm. The MAMP-triggered immunity (MTI) co-receptor double mutant, bak1-5/bkk1-1, exhibits a remarkable decrease in Fv/Fm compared to control plants during infection, underlining the importance of MTI mediated signalling in chloroplast immunity. Further probing the role of the chloroplast in immunity we unexpectedly found that high light uncouples plant immune signalling.

Xylem is a main road in plant long-distance communication. Through xylem plants transport water, minerals and myriad of signaling molecules. With the onset during early embryogenesis, the development of xylem tissues relays on hormone gradients, activity of unique transcription factors, distribution of mobile miRNAs and receptor-ligand pathways. These regulatory mechanisms are often interconnected and all together contribute to the plasticity of water conducting tissue. Remarkably, root xylem carries water to all above-ground organs and therefore influences all aspects of plant growth. Because of the global warming and increasing water deficit, we need to come up with solutions for the crops of the future. It is clear that structure of water conducting elements directly impacts water transport within the plant. Among plant pathogens- vascular wilts attacking xylem -are the most harmful. Our knowledge about xylem anatomy and rewiring ability could bring the solutions against these diseases. In this review we summarize the recent findings on the molecular mechanisms of xylem formation with a special attention to the cellular changes, and cell wall rearrangements that are necessary to create functional capillaries. We emphasize the impact of abiotic factors and pathogens on xylem plasticity and discuss multidisciplinary approach to model xylem in crops.

Flowering time is a major determinant of adaptation, fitness and yield in the allopolyploid species rapeseed (Brassica napus). Despite being a close relative to Arabidopsis thaliana, little is known about the timing of floral transition and which genes govern this process. Winter, semi-winter and spring type rapeseed have important life history characteristics that differ in vernalization requirements for flowering and are important for growing rapeseed in different regions of the world. In this study, we investigated the timing of vernalization-driven floral transition in winter rapeseed and the effect of photoperiod and developmental age on flowering time and vernalization responsiveness. Microscopy and whole transcriptome analysis at the shoot apical meristems of plants grown under controlled conditions showed that floral transition is initiated within few weeks of vernalization. Certain Bna.SOC1 and Bna.SPL5 homeologs were among the induced genes, suggesting that they are regulating the timing of cold-induced floral transition. Moreover, the flowering response of plants with shorter pre-vernalization period correlated with a delayed expression of Bna.SOC1 and Bna.SPL5 genes. In essence, this study presents a detailed analysis of vernalization-driven floral transition and the aspects of juvenility and dormancy and their effect on flowering time in rapeseed.

The thylakoid membrane is in a temperature-sensitive equilibrium that shifts repeatedly during the life cycle in response to ambient temperature or solar irradiance. Plants respond to seasonal temperature by changing their thylakoid lipid composition, while a more rapid mechanism for short-term heat exposure is required. The emission of the small organic molecule isoprene has been postulated as one such possible rapid mechanism. The protective mechanism of isoprene is not known, but some plants emit isoprene during periods of high-temperature stress. In this work, we investigate the dynamics and structure for lipids within a thylakoid membrane at different temperatures and varied isoprene content using classical molecular dynamics simulations. The results are compared with experimental findings from across the literature for temperature-dependent changes in the lipid composition and shape of thylakoids. We find that the surface area, volume, and flexibility of the membrane, as well as the lipid diffusion, increase with temperature, while the membrane thickness decreases. Saturated thylakoid 34:3 glycolipids derived from eukaryotic synthesis pathways exhibit significantly different dynamics than lipids from prokaryotic synthesis paths, which could explain the upregulation of specific lipid synthesis pathways at different temperatures. Increasing isoprene concentration was not observed to have a significant thermoprotective effect on the thylakoid membranes, and that isoprene readily permeated the membrane models tested here.