The interplay of auxin and brassinosteroid signaling tunes root growth under low and different nitrogen forms

Abstract

The coordinated signaling activity of auxin and brassinosteroids (BRs) is critical for optimal plant growth and development. Nutrient-derived signals regulate root growth by modulating the levels and spatial distribution of growth hormones to optimize nutrient uptake and assimilation. However, the effect of the interaction of these two hormones and their signaling on root plasticity during low and differential availability of nitrogen (N) forms (NH4+/NO3-) remains elusive. We demonstrate that root elongation under low nitrogen (LN) is an outcome of the interdependent activity of auxin and BR signaling pathways in Arabidopsis (Arabidopsis thaliana). LN promotes root elongation by increasing BR-induced auxin transport activity in the roots. Increased nuclear auxin signaling and its transport efficiency have a distinct impact on root elongation under LN conditions. High auxin levels reversibly inhibit BR signaling via BRI1 KINASE INHIBITOR1 (BKI1). Using the tissue-specific approach, we show that BR signaling from root vasculature (stele) tissues is sufficient to promote cell elongation and, hence, root growth under LN condition. Further, we show that N form-defined root growth attenuation or enhancement depends on the fine balance of BR and auxin signaling activity. NH4+ as a sole N source represses BR signaling and response, which in turn inhibits auxin response and transport, whereas NO3- promotes root elongation in a BR signaling–dependent manner. In this study, we demonstrate the interplay of auxin and BR-derived signals, which are critical for root growth in a heterogeneous N environment and appear essential for root N foraging response and adaptation.

Exogenous brassinosteroids promotes root growth, enhances stress tolerance, and increases yield in maize

“…The BRs signaling kinase BSK3 allele provides a target for improving root growth of crops growing under limited nitrogen conditions. 35 , 36 Given their vital function in plant growth, development, and reproduction, exogenous application of BRs can increase the yield of various plants and improve crop quality. 37 BRs is also nontoxic and beneficial to human health, acting as a potent antioxidant and neuroprotective agent in Parkinson’s disease 38 and may improve keratitis in mice.…”

Brassinosteroids mediate moderate soil‐drying to alleviate spikelet degeneration under high temperature during meiosis of rice

“…Root‐sourced hormones are considered to be the most crucial in a root function and are closely associated with the growth and development of aboveground plants (Jia et al, 2022). It was reported that an appropriate increase in BRs biosynthetic and/or signal transduction can effectively promote root growth and development, water and nutrient absorption, as well as alleviate adversity stress‐induced injury in plants (Devi et al, 2022; Jia et al, 2019; Lv et al, 2018; Singh et al, 2018; Wei & Li 2016; Xing et al, 2022; Zhang et al, 2021). The present results showed that the decreases in root oxidation activity, root active absorption area and flow rate of root xylem sap were accompanied by drastically reduced BRs contents in roots at HT, whereas these reduced parameters in HT‐WW‐treated plants could be greatly improved and were comparable to those of NT‐WW‐treated plants in the HT‐MD treatment (Figures 2c,d and 3a–c).…”

The alleviation of ammonium toxicity in plants

“…The NH 4 + toxic symptoms are partially reused by exogenously supplied BR. In addition, BR treatment evidently provokes NH 4 + ‐triggered PIN2 suppression and nuclear auxin signaling, suggesting that auxin functions downstream of BR signaling in the regulation of NH 4 + detoxification (Devi et al, 2022).…”

“…-triggered PIN2 suppression and nuclear auxin signaling, suggesting that auxin functions downstream of BR signaling in the regulation of NH 4 + detoxification (Devi et al, 2022).…”