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

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.

BZR1 and BES1 transcription factors mediate brassinosteroid control over root system architecture in response to nitrogen availability

“…It is known that low concentrations of BR promote while high concentrations inhibit root growth ( Müssig et al., 2003 ; Jantapo et al., 2021 ). To see the effect of BR levels on RSA of Arabidopsis seedlings under different N conditions, 3-day-old seedlings were transferred to treatment plates supplemented with 0 nM, 0.03 nM, 0.05 nM, 0.5 nM, and 1.0 nM EBR under N-sufficient (11,400 µM) and N-deficient (250 µM and 10 µM) conditions.…”

Transcriptome Analysis of Rice Root Tips Reveals Auxin, Gibberellin and Ethylene Signaling Underlying Nutritropism

“…These regions lie within the meristem zone according to the general morphology of the main root tips of rice ( Li et al. 2015 , Jantapo et al. 2021 ).…”