4.2 Drought response differences of S. krylovii among different
regions
Plant drought responses have been proven highly variable and
significantly associated with higher environmental heterogeneity (Akman
et al., 2021). In this study, the diagram based on gene expressions for
all treatments also showed that individuals from eastern and middle
regions under the same soil moisture treatment showed more similarity
(Fig. 3), as shown by physiological traits in Table 2. In addition,
under heavy drought treatment, the decline rates of the number of
tillers in the western region were much smaller and the Pn ofindividuals from the western region were significantly greater
than that of the other two regions (Table 2). Furthermore, under heavy
drought treatment, the KEGG enriched pathways in the individuals from
the western region were less than in the other two regions, which
indicated that individuals from the western region were tolerant while
individuals in the other two regions were sensitive to heavy drought
treatment (Guo et al., 2023). All these findings indicated that the
greater drought tolerance of individuals from the western region,
which could explain the eastern shifts of the distribution areas ofS. krylovii to some extent (Liu, 2004).
Based on KEGG on DEGs between heavy drought treatment vs control, the
present study showed that there were different response strategies
between individuals from the western region and those from the other two
regions. For DEGs of RNA-seq data, both up-regulated and
down-regulated genes are important for species responses to
stress conditions. However, sorting down-regulated genes into tolerance
and response strategies is difficult due to the fact that many cellular
processes are attenuated under stress conditions (such as heavy drought
stress) to reduce growth and initiate dormancy (Bushman et al., 2021).
Therefore, most studies have paid more attention to the significantly
enriched pathways of DEGs .
First, metabolism of other amino acids and energy metabolism were
significantly enriched and up-regulated in individuals from the eastern
and middle regions but not the western region (Fig. 5a & b; Table S3 &
S4). Many studies have shown that drought stress leads to changes in
amino acid content and energy metabolism in plants (Heinemann et al.,
2021; Ünlüsoy et al., 2023). Amino acid accumulation has a twofold role,
their availability for protein biosynthesis and accelerated recovery
after stress and osmoprotectant activity (Ashrafi, 2018). Wan et al.
(2021) have found that differentially expressed metabolites related to
the acid metabolism pathways may be key factors affecting drought
resistance differences in two cherry (Prunus pseudocerasus L.)
rootstocks. Plants can accumulate soluble proteins to maintain cell
expansion and cell membrane stability, thereby protecting macromolecules
from damage under drought stress (Fang & Xiong, 2015). Zhu et al.
(2017) have found that individuals of Sorghum sudanense were
significantly enriched in photosynthesis (energy metabolism) by KEGG on
DEGs between drought treatment vs control. Plant photosynthesis can
directly affect plant tissue material production and is extremely
sensitive to environmental changes, thus, drought stress has a great
impact on plant photosynthesis (Basu et al., 2016).
Second, carbohydrate metabolism and biosynthesis of other secondary
metabolites were significantly enriched and up-regulated in individuals
from the western region (Fig. 5c; Table S5). In response to drought
stress, an increase in the content of flavonoids can help eliminate
excess reactive oxygen species in the plant and help the plant to better
adapt to the conditions of drought stress (Nakabayashi et al., 2014).
Many studies have shown that drought stress usually induces the
accumulation of flavonoids in plants (Gao et al., 2021; Yu et al.,
2022). Glycolysis is an important metabolic pathway in carbohydrate
metabolism, and changes in glycolysis and gluconeogenesis are considered
an essential feature of plant adaptation to abiotic stresses (Broeckling
et al., 2005). Shi et al. (2020) have conducted transcriptomic analysis
of okra (Abelmoschus esculentus ) under drought stress and shown
that most of the DEGs were mainly enriched in carbon metabolism,
secondary metabolite synthesis, and glycolysis / glycolysis, etc. The
increase in soluble sugar content plays an important role as a signaling
molecule for plant growth and development under environmental stress,
also is involved in the process of cellular carbon and energy metabolism
(Rolland et al., 2006; Shahbazy et al., 2020). Using peach
(Salvadora persica ) as the experimental material, Rangani et al.
(2020) have found that galactose is up-regulated to provide roles such
as osmoregulation, energy for antioxidant defense, carbon skeleton for
secondary metabolite synthesis, and stress signaling under drought
stress.