Molecular basis of shade toleranceidentification of novel components

Abstract

To deal with the limitation of light that might cause the shade cast by neighboring vegetation, plants have evolved two different and divergent strategies: avoidance, like Arabidopsis thaliana and tolerance, like Cardamine hirsuta. When shaded, shade-avoider species display a suite of traits and responses to adapt growth and development as a way to "escape" from shade, called globally the shade avoidance syndrome (SAS). Among these traits are found accelerated elongation of stems (hypocotyls and internodes) and leaf petioles, also elevated leaf angles to the horizontal, reduced branching and early flowering. Conversely, shade-tolerant species do not outgrow the neighboring plants (i.e., their hypocotyls do not elongate in response to plant shade). While the molecular basis of shade avoidance has been heavily studied, such as several transcriptional regulators are central to plant responses to vegetation proximity, including the positive regulator PHYTOCHROME INTERACTING FACTORs (PIFs) and the antagonistic ELONGATED HYPOCOTYL 5 (HY5) and LONG HYPOCOTYL IN FAR-RED 1 (HFR1). However, much less is known about how shade tolerance works, so we are beginning to explore how shade tolerant-plant modulate vegetation proximity by using C. hirsuta, a close relative of A. thaliana. We demonstrated that C. hirsuta HFR1 interacted weaklier with COP1 than A. thaliana HFR1, which causing the has higher biological activity and stability than. In addition, C. hirsuta HY5 inhibits hypocotyl elongation in both shade and white light conditions by constraining the growth-related hormones, such as auxin. Moreover, C. hirsuta PIF7 has a role in promoting hypocotyl elongation in shade but only in a phytochrome A (phyA) deficient background. We show that a higher activity of negative regulators, including HFR1 and HY5, whereas a lower activity of positive regulators, like PIF7 when compared to A. thaliana, resulting in the shade tolerance habit of C. hirsuta. Besides, PROTEOLYSIS6 (PRT6) may be a newly A.thaliana shade avoidance regulator, which affects several aspects of plant development, including delayed dark induced senescence (DIS), thermal induced morphogenesis (TIM) and shade-induced hypocotyl elongation. Mutations in different locations of the PRT6 gene may cause differential responses of hypocotyls to shade.