BRX (BREVIS RADIX) is a small gene family specific to plants. It serves as a key regulator of plant developmental processes, particularly root elongation, shoot growth, stomatal development and tiller angle, which have direct relevance for crop improvement. Therefore, in this study, identification and functional characterization of BRX family genes was carried out in cereal crop wheat (Triticum aestivum).

Five BRX family genes were identified in wheat genome.Phylogenetic and synteny analyses revealed evolutionary conservation among BRX proteins from monocot species. Expression analysis ofBRXgenes viz. TaBRXL1 to TaBRXL4 was carried out in different tissues at developmental stages and under abiotic stresses. TaBRXL1 was predominantly associated with developmental processes, whereas TaBRXL2 exhibitedextensive regulation by development, hormones, and various abiotic stresses. The remaining TaBRX genes displayed differential expression levels and distinct patterns during developmental stages and stress conditions.

Further, we functionally characterized TaBRXL2A by gain-of-function in Arabidopsis. Overexpression of TaBRXL2A resulted in longer primary roots under control and exogenous hormone treatments as compared to wild type plants. Overexpression lines also exhibited significant differences such as increased rosette size, higher leaf number and leaf size as compare to wild type. At reproductive stage, overexpression lines exhibited wider siliques and higher grain weight per plant. During drought stress, overexpression lines displayed improved tolerance in terms of higher chlorophyll retention and lower oxidative stress, thereby leading to significant recovery from drought stress.

The analysis suggests that the inherent lower stomatal density in the leaves of overexpression lines and higher stomatal closure in response to ABA might contribute to lower water loss from the overexpression lines.

The TaBRX proteins showed homotypic and heterotypic interactions with BRX domain containing proteins. TaBRXL2A protein exhibited membrane localization, presence of conserved residues at the N-terminal for palmitoylation, and phosphosites in the linker region, indicating its potential involvement in protophloem differentiation and stomatal lineage.

Thus, we identified a TaBRX family gene that participates in developmental pathways vital for plant growth and augments drought tolerance in Arabidopsis.