The BRASSINOSTEROID INSENSITIVE1–LIKE3 Signalosome Complex Regulates Arabidopsis Root Development    

Abstract

Brassinosteroid (BR) hormones are primarily perceived at the cell surface by the leucine-rich repeat receptor-like kinase BRASSINOSTEROID INSENSITIVE1 (BRI1). In Arabidopsis thaliana, BRI1 has two close homologs, BRI1-LIKE1 (BRL1) and BRL3, respectively, which are expressed in the vascular tissues and regulate shoot vascular development. Here, we identify novel components of the BRL3 receptor complex in planta by immunoprecipitation and mass spectrometry analysis. Whereas BRI1 ASSOCIATED KINASE1 (BAK1) and several other known BRI1 interactors coimmunoprecipitated with BRL3, no evidence was found of a direct interaction between BRI1 and BRL3. In addition, we confirmed that BAK1 interacts with the BRL1 receptor by coimmunoprecipitation and fluorescence microscopy analysis. Importantly, genetic analysis of brl1 brl3 bak1-3 triple mutants revealed that BAK1, BRL1, and BRL3 signaling modulate root growth and development by contributing to the cellular activities of provascular and quiescent center cells. This provides functional relevance to the observed protein-protein interactions of the BRL3 signalosome. Overall, our study demonstrates that cell-specific BR receptor complexes can be assembled to perform different cellular activities during plant root growth, while highlighting that immunoprecipitation of leucine-rich repeat receptor kinases in plants is a powerful approach for unveiling signaling mechanisms with cellular resolution in plant development.

A receptor-like protein mediates the response to pectin modification by activating brassinosteroid signaling

“…In contrast to the results with bri1 cnu1 , RLP44 overexpression was able to rescue the phenotype of the bak1-4 mutant (30, 31) (Fig. 3 F and G), possibly reflecting the different levels of genetic redundancy in the BRI1-like and BAK1/SERK gene families (32,33): BAK1/ SERK3 is partially redundant with SERK1 and SERK4, and a bri1 null-like phenotype is only observed in the absence of all three SERKs (33). Thus, RLP44-mediated rescue of bak1-4, but not of bri1 cnu1 might be explained by a possible interaction of RLP44 with the two other redundant SERKs (see below).…”

Translatome analyses capture of opposing tissue-specific brassinosteroid signals orchestrating root meristem differentiation

“…(Scale bar, 50 μM.) three BR receptors (12), revealed unequal redundancy between these receptors. Stele-localized BRI1 had the most significant impact on restraining the extent of stem cell daughter proliferation.…”

“…In addition, enhanced BR signaling triggered by impaired spatial distribution of BRI1, limits cell elongation and whole root growth (11). BRs are also perceived by BRI1-Like 1 (BRL1) and BRI1-Like 3 (BRL3), two BRI1 homologs that are confined to the stem cell niche and the stele, where they promote QC cell divisions (12)(13)(14). BRI1 acting in the epidermis promotes stem cell daughter divisions, stimulating root meristem size and whole root growth via an unknown signal (9).…”

Brassinosteroid Regulates Cell Elongation by Modulating Gibberellin Metabolism in Rice

“…Accordingly, we found that sd1 had longer roots while GA20-1ox had shorter roots compared with their respective wild types. Considering the unchanged root length in d2, d11, and even brd1, the most severe BR-deficient mutant (Supplemental Table 1) (Mori et al, 2002), rice root systems may have more complex mechanisms than aerial tissues that regulate growth (González-García et al, 2011;Fàbregas et al, 2013).…”