Supraoptimal Brassinosteroid Levels Inhibit Root Growth by Reducing Root Meristem and Cell Elongation in Rice.

Kewalee Jantapo,Juthamas Chaiwanon,Wenfei Wang,Watcharapong Wimonchaijit

doi:10.3390/plants10091962

Kewalee Jantapo, Juthamas Chaiwanon + Show 2 more

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https://doi.org/10.3390/plants10091962

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Abstract

Root growth depends on cell proliferation and cell elongation at the root meristem, which are controlled by plant hormones and nutrient availability. As a foraging strategy, rice (Oryza sativa L.) grows longer roots when nitrogen (N) is scarce. However, how the plant steroid hormone brassinosteroid (BR) regulates rice root meristem development and responses to N deficiency remains unclear. Here, we show that BR has a negative effect on meristem size and a dose-dependent effect on cell elongation in roots of rice seedlings treated with exogenous BR (24-epicastasterone, ECS) and the BR biosynthesis inhibitor propiconazole (PPZ). A genome-wide transcriptome analysis identified 4110 and 3076 differentially expressed genes in response to ECS and PPZ treatments, respectively. The gene ontology (GO) analysis shows that terms related to cell proliferation and cell elongation were enriched among the ECS-repressed genes. Furthermore, microscopic analysis of ECS- and PPZ-treated roots grown under N-sufficient and N-deficient conditions demonstrates that exogenous BR or PPZ application could not enhance N deficiency-mediated root elongation promotion as the treatments could not promote root meristem size and cell elongation simultaneously. Our study demonstrates that optimal levels of BR in the rice root meristem are crucial for optimal root growth and the foraging response to N deficiency.

Highlights

Root systems play important roles in water and nutrient acquisition
Our study demonstrates that optimal levels of BR in the rice root meristem are crucial for optimal root growth and the foraging response to N deficiency
To investigate how BR modulates root growth, germinated rice seeds were grown for 5 days (d) in media supplemented with various concentrations of a biologically active BR, 24-epicastasterone (ECS), and/or a BR biosynthesis inhibitor, propiconazole (PPZ)

Summary

Introduction

Root systems play important roles in water and nutrient acquisition. The developmental plasticity of root system architecture is crucial for crop adaptation to unfavorable environments, such as drought stress and nutrient deficiency stress. Understanding the mechanisms that control root growth is important for crop genetic improvement for sustainable agriculture, with the goal of reducing fertilizer application while maintaining crop productivity. Root growth is determined by cell division and elongation at the root tip, where cells are organized along the longitudinal axis in distinct developmental zones. At the apical side of the root tip, cells are actively dividing in the meristem zone. As the cells leave the meristem zone, they enter the elongation zone, where they rapidly elongate and reach their mature size before entering the maturation zone to undergo differentiation [2]

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