Brassinosteroid decreases cadmium accumulation via regulating gibberellic acid accumulation and Cd fixation capacity of root cell wall in rice (Oryza sativa)

The precise mechanism behind the association between plants' reactions to cadmium (Cd) stress and brassinosteroid (BR) remains unclear. In the current investigation, Cd stress quickly increased the endogenous BR concentration in the rice roots. Exogenous BR also increased the hemicellulose level in the root cell wall, which in turn increased its capacity to bind Cd. Simultaneously, the transcription level of genes responsible for root Cd absorption was decreased, including Natural Resistance-Associated Macrophage Protein 1/5 (OsNRAMP1/5) and a major facilitator superfamily gene called OsCd1. Ultimately, the increased expression of Heavy Metal ATPase 3 (OsHMA3) and the decreased expression of OsHMA2, which was in charge of separating Cd into vacuoles and translocating Cd to the shoots, respectively, led to a decrease in the amount of Cd that accumulated in the rice shoots. In contrast, transgenic rice lines overexpressing OsGSK2 (a negative regulator in BR signaling) accumulated more Cd, while OsGSK2 RNA interference (RNAi) rice line accumulated less Cd. Furthermore, BR increased endogenous Gibberellic acid (GA) level, and applying GA could replicate its alleviative effect. Taken together, BR decreased Cd accumulation in rice by mediating the cell wall's fixation capacity to Cd, which might relied on the buildup of the GA.

BR deficiency causes increased sensitivity to drought and yield penalty in cotton

BACKGROUND

Brassinosteroids (BRs) play crucial roles in drought tolerance, but the underlying molecular mechanisms remain unclear in the important oilseed and fiber crop, cotton (Gossypium hirsutum L.).

RESULTS

To elucidate how BRs mediate drought tolerance in cotton, a cotton brassinosteroid (BR)-deficient mutant, pag1 (pagoda1), was employed for analysis. Importantly, the pag1 mutant showed increased sensitivity to drought stress, with shorter primary roots and fewer lateral roots. The number of stomata was significantly increased in the mutant, and the stomata aperture was much wider than that of the control plants. These mutant plants therefore showed an increased water loss rate. Furthermore, the abscisic acid (ABA) content, photosynthetic efficiency and starch content of the mutant were significantly lower than those of the wild type. The overall performance of the mutant plants was worse than that of the wild-type control under both normal and drought conditions. Moreover, Proteomic analysis revealed reduced levels of stress-related proteins in pag1 plants.

CONCLUSIONS

These results suggest that BRs may modulate the drought tolerance of cotton by regulating much genes that related to drought stress and multiple organ responses to drought, including root growth, stomata development, the stomata aperture and photosynthesis. This study provides an important basis for understanding drought resistance regulated by BRs and cultivating drought-resistant cotton lines.

Brassinosteroid reduces ABA accumulation leading to the inhibition of ABA-induced stomatal closure

Proper regulation of stomatal movement in response to various environmental stresses or developmental status is critical for the adaptation of many plant species to land. In plants, abscisic acid (ABA)-induced stomatal closure is a well-adapted method of regulating water status. In addition to ABA, we previously showed that plant-specific steroidal hormone, brassinosteroid (BR), also induces stomatal closure; however, BR modulates ABA-induced stomatal closure negatively at high concentrations. In this study, we further investigated the cross-talk between ABA and BR in relation to stomatal movement. In contrast to previous reports that ABA-induced stomatal closure was inhibited by brassinolide (BL), the most active BR, we showed that BL-induced stomatal closure was enhanced by ABA, indicating that the sequence of ABA or BL treatments led to different results. We found that this phenomenon occurred because the guard cells still had the capacity to be closed further by ABA, as the degree of stomatal closure by BL was always less than that by ABA. We also found that BL-induced stomatal closure required Open Stomata 1 (OST1) activity and the induced expression of OST1 was indifferent to the sequence of ABA and/or BL treatments. In addition, we examined the underlying mechanism by which inhibition of ABA-induced stomatal closure by BL occurred. We revealed that the downregulation of ABA-biosynthetic genes by BL resulted in a lower accumulation of ABA. These results suggested that the regulation of stomatal movement is finely controlled by the combined effects of plant hormones, ABA and BR.

Brassinosteroid's multi-modular interaction with the general stress network customizes stimulus-specific responses in Arabidopsis

Adaptation to fluctuating environmental conditions is a universal feature of plant life, governed by fundamental mechanisms optimizing resource allocation. This balance is achieved in part through tightly regulated communication networks among growth and stress response signaling pathways. Understanding the communication modules between brassinosteroids (BRs), the ubiquitous hormones known to control growth and stress adaptation, and the general stress response (GSR), a rapid and transient transcriptional output in response to perturbations, provides an optimal platform to unravel new facet(s) of plant stress adaptation. Here, we explore communication facets of BR with GSR via in planta quantification of the GSR in Arabidopsis expressing luciferase driven by a functional GSR cis-element, the Rapid Stress Response Element (4xRSRE:LUC). We establish that application of exogenous BR suppresses microbe-associated molecular pattern-activated GSR, but enhances the wound-triggered GSR. The enhanced wound-activated GSR in BR-treated plants results in a greater wound-induced resistance to Botrytis cinerea. A combination of molecular genetics using BR signaling mutants and application of an activator of BR signaling, bikinin, confirms these results and places the chief point of BR-GSR interaction downstream of potential membrane receptor circuitry. These results support a multi-modular interaction between BRs and stress signaling, instrumental in customizing stimulus-specific responses in Arabidopsis.