Exploring the Brassinosteroid Signaling in Monocots Reveals Novel Components of the Pathway and Implications for Plant Breeding.

Damian Gruszka

doi:10.3390/ijms21010354

Abstract

Brassinosteroids (BRs) are a class of steroidal phytohormones which are key regulators of diverse processes during whole life cycle of plants. Studies conducted in the dicot model species Arabidopsis thaliana have allowed identification and characterization of various components of the BR signaling. It is currently known that the BR signaling is interconnected at various stages with other phytohormonal and stress signaling pathways. It enables a rapid and efficient adaptation of plant metabolism to constantly changing environmental conditions. However, our knowledge about mechanism of the BR signaling in the monocot species is rather limited. Thus, identification of new components of the BR signaling in monocots, including cereals, is an ongoing process and has already led to identification of some monocot-specific components of the BR signaling. It is of great importance as disturbances in the BR signaling influence architecture of mutant plants, and as a consequence, the reaction to environmental conditions. Currently, the modulation of the BR signaling is considered as a target to enhance yield and stress tolerance in cereals, which is of particular importance in the face of global climate change.

Highlights

In the modern agricultural practices crops are grown at high planting density and with relatively high nitrogen supply
This review presented the updated view on the current model of the BR signaling in rice and other cereals
The results obtained mainly in rice and in other monocot species allowed for identification of some BR signaling components and their functions which are unique for the monocots

Summary

Introduction

In the modern agricultural practices crops are grown at high planting density and with relatively high nitrogen supply. A feedback suppression of the BR-biosynthesis gene expression in response to exogenous BR application functions normally in the d1 mutant (in contrast to the d61 mutants of the OsBRI1 gene in which the feedback mechanism is disturbed) This indicates that the OsD1/RGA1 protein in rice is involved in the distinct BR signaling relay, independent of the OsBRI1 receptor kinase [47,66,67,68]. Perception of BR was shown to activate the membrane-bound mitogen-activated protein kinase (MAPK) and cytosolic CDPK protein, but this effect was reversed in the mutant plants defective in the OsBRI1 function It indicated that the signaling pathways downstream of the BR-mediated activation of MAPK and CDPK are parallel, and may involve other components in addition to OsBRI1 to mediate the BR response [76] (Figure 1). The ELT1 protein and its positive effect on the BR signaling is probably specific to monocots [36]

Regulation of the BR Signaling Relay in Monocots

Regulation of the BR-Dependent Gene Expression in Monocots

Findings

Conclusions