Abstract
Brassinosteroids, the steroid hormones of plants, control physiological and developmental processes through its signaling pathway. The major brassinosteroid signaling network components, from the receptor to transcription factors, have been identified in the past two decades. The development of biotechnologies has driven the identification of novel brassinosteroid signaling components, even revealing several crosstalks between brassinosteroid and other plant signaling pathways. Herein, we would like to summarize the identification and improvement of several representative brassinosteroid signaling components through the development of new technologies, including brassinosteroid-insensitive 1 (BRI1), BRI1-associated kinase 1 (BAK1), BR-insensitive 2 (BIN2), BRI1 kinase inhibitor 1 (BKI1), BRI1-suppressor 1 (BSU1), BR signaling kinases (BSKs), BRI1 ethyl methanesulfonate suppressor 1 (BES1), and brassinazole resistant 1 (BZR1). Furthermore, improvement of BR signaling knowledge, such as the function of BKI1, BES1 and its homologous through clustered regularly interspaced short palindromic repeats (CRISPR), the regulation of BIN2 through single-molecule methods, and the new in vivo interactors of BIN2 identified by proximity labeling are described. Among these technologies, recent advanced methods proximity labeling and single-molecule methods will be reviewed in detail to provide insights to brassinosteroid and other phytohormone signaling pathway studies.
Highlights
Brassinosteroids (BRs) are plant steroid hormones critical in numerous developmental and physiological processes, such as stem elongation, vascular differentiation, seed size, male fertility, flowering time, senescence, cell division, and resistance to biotic and abiotic stresses [1,2]
Without BRs, BR-insensitive 1 (BRI1) is maintained at an inactive state by its C-terminal autoinhibition [6], and by a negative regulator, BRI1 kinase inhibitor 1 (BKI1), which prevents the interaction of BRI1 with its coreceptor BRI1-associated kinase 1 (BAK1) [7,8]
Jiang et al examined whether the function of BKI1 and membrane associated kinase regulator 1 (MAKR1) is redundant by disrupting the C-terminal region of BKI1 using clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9; they found that the genes were not redundant in BR signaling [42]
Summary
Brassinosteroids (BRs) are plant steroid hormones critical in numerous developmental and physiological processes, such as stem elongation, vascular differentiation, seed size, male fertility, flowering time, senescence, cell division, and resistance to biotic and abiotic stresses [1,2]. Because of the discovery of the BR receptor BR-insensitive 1 (BRI1) [3,4], several key components of the BR signaling pathway have been reported (Figure 1). In the downstream signaling pathway, two main transcription factors, BRI1 ethyl methanesulfonate (EMS) suppressor 1 (BES1) and brassinazole resistant 1 (BZR1), are phosphorylated by BR-insensitive 2 (BIN2), and some members of 14-3-3 proteins can bind and retain the phosphorylated BES1 and BZR1 in the cytoplasm [9–12]. MMoolleeccuullaarr ggeenneettiiccss pprroovviiddeess tthhee fuunnddaammeennttaallss ffoorr the study of signaling pathways. We illustrate how these technologies have been used in BR network studies, with emphases on PL and single-molecule technology. We review the development of these two methods, highlighting their application in planta The coverage of these methods can help researchers in the field gain new insights for their own studies
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