Jasmonic Acid coordinates with Light, Glucose and Auxin signalling in Regulating Branching Angle ofArabidopsisLateral Roots

Abstract

The role of jasmonates (JAs) in root growth and development and plants response to external stimuli is already known. However, its role in lateral root (LR) development remains perplexing. Our work identifies methyl jasmonate (MeJA) as a crucial phytohormone in determining the branching angle of Arabidopsis LRs. MeJA inclines the LRs to a more vertical orientation which was dependent on JAR1-COI1-MYC2,3,4 signalling. Our work highlights the dual role of light acting with MeJA in governing the LR angle. Glucose (Glc), produced by light mediated photosynthesis induces wider branching angles. Combining physiological and molecular assays, we reveal that Glc antagonizes the MeJA response via HEXOKINASE1 (HXK1) mediated signalling and by stabilizing JAZ9. Moreover, physiological assays using auxin mutants; binding of MYC2 on the promoters of auxin biosynthetic gene CYP79B2 and LAZY2 and asymmetric distribution of DR5::GFP and PIN2::GFP pinpoints the role of an intact auxin machinery required by MeJA for vertical growth of LRs. We also demonstrate that light perception through PHYTOCHROMES (PHYA and PHYB) and LONG HYPOCOTYL5 (HY5) are indispensable for inducing vertical angles by MeJA. Thus, our investigation highlights antagonism between light and Glc signalling and how they interact with JA-auxin signals to optimize the branching angle of LRs.

Understanding the Intricate Web of Phytohormone Signalling in Modulating Root System Architecture

“…JA signalling transcription factor MYC2 directly activates the transcription of CYP79B2 , an auxin biosynthetic gene, and LAZY2/4 in the regulation of LR angle. In addition, JA treatment also affects auxin transport machinery and PIN2 localization in the stage II LR, leading to a downward LR orientation ( Figure 6 B) [ 198 ]. The Arabidopsis R2R3-MYB transcription factor FOUR LIPS (FLP) and its paralog, MYB88, act redundantly but differently in the regulation of primary and LR gravity responses.…”

“…Moreover, these interactions do not occur via a simple linear mechanism; rather, there are many feedback loops and the involvement of various downstream activators and repressors that drive a single development output robustly. For example, binding of MYC2 transcription factor on the promoters of LAZY2 , LAZY4 , and auxin-responsive gene CYP79B2 leads to gravitropic bending of LRs [ 198 ]. A recent review by Semeradova et al 2020 summarizes that auxin transport machinery is post-translationally modified by multiple hormones that enable the rapid modulation of the auxin flow to control plant growth and development [ 204 ].…”