Boron deficiency‐induced root growth inhibition is mediated by brassinosteroid signalling regulation in Arabidopsis

Abstract

Summary Brassinosteroids (BRs) are pivotal phytohormones involved in the control of root development. Boron (B) is an essential micronutrient for plants, and root growth is rapidly inhibited under B deficiency conditions. However, the mechanisms underlying this inhibition are still unclear. Here, we identified BR‐related processes underlying B deficiency at the physiological, genetic, molecular/cell biological and transcriptomic levels and found strong evidence that B deficiency can affect BR biosynthesis and signalling, thereby altering root growth. RNA sequencing analysis revealed strong co‐regulation between BR‐regulated genes and B deficiency‐responsive genes. We found that the BR receptor mutants bri1‐119 and bri1‐301 were more insensitive to decreased B supply, and the gain‐of‐function mutants bes1‐D and pBZR1‐bzr1‐D exhibited insensitivity to low‐B stress. Under B deficiency conditions, exogenous 24‐epibrassinolide rescued the inhibition of root growth, and application of the BR biosynthesis inhibitor brassinazole exacerbated this inhibitory effect. The nuclear‐localised signal of BES1 was reduced under low‐B conditions compared with B sufficiency conditions. We further found that B deficiency hindered the accumulation of brassinolide to downregulate BR signalling and modulate root elongation, which may occur through a reduction in BR6ox1 and BR6ox2 mRNA levels. Taken together, our results reveal a role of BR signalling in root elongation under B deficiency.

Defects in meristem maintenance, cell division, and cytokinin signaling are early responses in the boron deficient maize mutant tassel‐less1

“…Therefore, defects in cell division could be an early response upon boron deficiency in maize. These findings are supported by recent evidence from Arabidopsis RAMs, where cell division was found to be an early target of the boron deficiency response (Poza‐Viejo et al, 2018; Zhang et al, 2020). Our findings suggested that early boron responses are at least in part conserved between the Arabidopsis RAM and the maize tassel meristem.…”

“…Therefore, defects in cell division could be an early response upon boron deficiency in maize. These findings are supported by recent evidence from Arabidopsis RAMs, where cell division was found to be an early target of the boron deficiency response(Poza-Viejo et al, 2018;Zhang et al, 2020). Our findings suggested that early boron responses are at least in part conserved between the Arabidopsis RAM and the maize tassel meristem.Reductions in cell division in the SAM were correlated with reduced WUS levels in Arabidopsis(Yadav et al, 2010) and in boron deficient roots cell division defects precede the loss of the quiescent center (QC) (as judged by the loss of the QC marker QC46:GUS) (Poza-Viejo…”

“…Boron deficiency leads to a cessation of growth particularly in meristematic regions (Sommer & Sorokin, 1928), yet the underlying molecular mechanisms are not fully understood. Substantial progress in understanding such molecular mechanisms has been made by investigating the Arabidopsis RAM (Abreu et al, 2014; Camacho‐Cristóbal et al, 2015; Gómez‐Soto et al, 2019; Martín‐Rejano et al, 2011; Poza‐Viejo et al, 2018; Zhang et al, 2020), using transfer assays of young seedlings grown on plates with different boron concentrations (as reviewed in Matthes et al, 2020). Molecular mechanisms affected by boron deficiency in maize shoot meristems are not yet known.…”

“…, yet the underlying molecular mechanisms are not fully understood. Substantial progress in understanding such molecular mechanisms has been made by investigating the Arabidopsis RAM(Abreu et al, 2014;Camacho-Crist obal et al, 2015;G omez-Soto et al, 2019;Martín-Rejano et al, 2011;Poza-Viejo et al, 2018;Zhang et al, 2020), using transfer assays ofT A B L E 3 (Continued) young…”

Identification and expression profiling of toxic boron-responsive microRNAs and their targets in sensitive and tolerant wheat cultivars

“…Under B toxicity, a substantial decrease in chlorophyll content (Chen et al, 2014) and structural changes in thylakoid membranes suggest that RERs may be involved in the development of B toxicity symptoms in plants. Surprisingly, the primary root growth is inhibited under B deficiency due to the down-regulation of BR biosynthesis genes and reduction in the active BR levels in Arabidopsis roots (Zhang et al 2021). BRs are also responsible for the inhibition of shoot growth under B deficiency (Eggert and von Wirén, 2017).…”