Plants transition through distinct stages as they develop, the timing of which, significantly impacts large-scale ecological and evolutionary processes. Vegetative phase change (VPC), the developmental transition from juvenile to adult vegetative growth, has been well studied at the molecular level however, little is known about its importance for plant performance and physiological functioning. VPC is regulated by an evolutionary conserved microRNA, miR156, in land plants from mosses to angiosperms. Young plants in the juvenile phase have high expression levels of miR156. As a plant ages, miR156 expression declines, alleviating repression of its target genes and transitioning the plant into the adult phase. Being that this transition has been conserved throughout much of plant evolution, it is likely to have significant consequences for plant performance. In this study, variation in physiological and morphological characteristics between juvenile and adult leaves of four diverse species, Zea mays, Passiflora edulis, Populus tremula x alba, and Arabidopsis thaliana, were analyzed. Further, whether or not these traits translate into variation in plant performance under environmental stress was examined. Our objectives were to: 1) Identify if photosynthetic efficiency and capacity varies between leaves produced during the juvenile and adult stages of plant development, 2) determine if leaf morphological traits related to plant physiology differ between these leaves and 3) determine whether variation in traits between juvenile and adult leaves translate into variation in plant performance under environmental stress.
Results/Conclusions
Using miR156 mutants in all four species where the timing of VPC was modulated we were able to examine physiological and morphological traits specifically related to plant developmental stage. We found significant variation in photosynthetic properties between juvenile and adult leaves in all species including maximum photosynthetic rates and rates of photosynthetic light induction. Additionally, juvenile and adult leaves showed differences in morphology including specific leaf area, stomatal densities and venation, traits with major implications for foliar function. Lastly, when both mutants and natural genotypes with variation in the timing of VPC, resulting in plants with more or less juvenile leaves, were subjected to the environmental stresses of heat, drought and low light, there was a significant relationship between plant performance under some of these stresses and the timing of VPC. This research begins to uncover the role of vegetative development in plant physiology, potential mechanisms to be utilized in plant breeding programs and insight into the underpinnings that may have led to its evolutionary conservation.