Comparative analysis of differential gene expression indicates
divergence in ontogenetic strategies of leaves in two conifer genera
Abstract
In land plants, heteroblasty broadly refers to a drastic change in
morphology during growth through ontogeny. Juniperus flaccida and
Pinus cembroides are conifers of independent lineages known to
exhibit leaf heteroblasty between the juvenile and adult life stage of
development. Juvenile leaves of P. cembroides develop spirally on
the main stem and appear decurrent, flattened and needle-like; whereas,
adult photosynthetic leaves are triangular or semi-circular needle-like,
and grow in whorls on secondary or tertiary compact dwarf shoots. By
comparison, J. flaccida juvenile leaves are decurrent and
needle-like, and adult leaves are compact, short and scale-like.
Comparative analyses were performed to evaluate differences in anatomy
and gene expression patterns between developmental phases in both
species. RNA from twelve samples was sequenced and analyzed with
available software. They were assembled de novo from the RNA-Seq reads.
Following assembly, 63,741 high quality transcripts were functionally
annotated in P. cembroides and 69,448 in J. flaccida.
Evaluation of the orthologous groups yielded 4,140 shared gene families
among the four references (adult and juvenile from each species).
Activities related to cell division and development were more abundant
in juveniles than adults in P. cembroides, and more abundant in
adults than juveniles in J. flaccida. Overall, there were 509
up-regulated and 81 down-regulated genes in the juvenile condition of
P. cembroides and 18 up-regulated and 20 down-regulated in
J. flaccida. Gene interaction network analysis showed evidence of
co-expression and co-localization of up-regulated genes involved in cell
wall and cuticle formation, development, and phenylpropanoid pathway, in
juvenile P. cembroides leaves. Whereas in J. flaccida,
differential expression and gene interaction patterns were detected in
genes involved in photosynthesis and chloroplast biogenesis. Although
J. flaccida and P. cembroides both exhibit leaf
heteroblastic development, little overlap was detected and unique genes
and pathways were highlighted in this study.