Abstract
Brassinosteroids (BRs) are steroid hormones essential for different biological processes, ranging from growth to environmental adaptation in plants. The plant brassinosteroid-signaling kinase (BSK) proteins belong to a family of receptor-like cytoplasmic kinases, which have been reported to play an important role in BR signal transduction. However, the knowledge of BSK genes in plants is still quite limited. In the present study, a total of 143 BSK proteins were identified by a genome-wide search in 17 plant species. A phylogenetic analysis showed that the BSK gene originated in embryophytes, with no BSK found in green algae, and these BSK genes were divided into six groups by comparison with orthologs/paralogs. A further study using comparative analyses of gene structure, expression patterns and alternative splicing of BSK genes in Arabidopsis revealed that all BSK proteins shared similar protein structure with some exception and post-translation modifications including sumolyation and ubiquitination. An expression profile analysis showed that most Arabidopsis BSK genes were constitutively expressed in different tissues; of these, several BSK genes were significantly expressed in response to some hormones or abiotic stresses. Furthermore, reverse transcription-polymerase chain reaction (RT-PCR) assays showed that BSK5, BSK7, and BSK9 underwent alternative splicing in specific stress induced and tissue-dependent patterns. Collectively, these results lay the foundation for further functional analyses of these genes in plants.
Highlights
As sessile organisms, plants need to proceed in a coordinated manner to adapt to the constantly changing environment and react to stress conditions for growth and development
A genome-wide analysis of the brassinosteroid-signaling kinase (BSK) gene family was performed on the basis of the completed genome sequences
By investigating the extent of lineage-specific expansion of the BSK genes in plants, we found that the BSK gene originated in embryophytes (Figure 1A)
Summary
Plants need to proceed in a coordinated manner to adapt to the constantly changing environment and react to stress conditions for growth and development. Brassinosteroids (BRs) are generally known as important plant hormones that play fundamental roles in various cellular, physiological, and developmental processes during plant life cycle [1,2]. The direct binding of the BR ligand with BRI1 induces its association BRI1 with its co-receptor BRI1-ASSOCIATED RECEPTOR KINASE 1 (BAK1), enhancing the signaling output through reciprocal BRI1 transphosphorylation, inactivation of a glycogen synthase kinase-3 BRASSINOSTEROID INSENSITIVE 2 (BIN2) and activation of phosphatase BRI1 SUPPRESSOR 1 (BSU1), as well as the downstream transcription factors BRASSINAZOLE-RESISTANT 1 (BZR1) and BRI1-EMS-SUPPRESSOR 1 (BES1) [5,6,7,8]. The transcription factor gene family, in turn, controls the expression of numerous target genes, which control various cellular, physiological, and developmental processes [6,9]
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