Abstract
The BRS1 (BRI1 Suppressor 1) gene encodes a serine carboxypeptidase that plays a critical role in the brassinosteroid signaling pathway. However, its specific biological function remains unclear. In this study, the developmental role of BRS1 was investigated in Arabidopsis thaliana. We found that overexpressing BRS1 resulted in significantly more lateral roots in different Arabidopsis ecotypes (WS2 and Col-0) and in brassinosteroid mutants (bri1-5 and det2-28). Further research showed that BRS1 facilitates the process whereby lateral root primordia break through the endodermis, cortex, and epidermis. Consistent with this, BRS1 was found to be highly expressed in the root endodermis and accumulated in the extracellular space around the dome of the lateral root primordia. Taken together, these results highlight the role of BRS1 in the process of lateral root emergence and provide new insight into the role of serine carboxypeptidases in plant root development.
Highlights
BRS1 (BRI1 Suppressor 1) is a serine carboxypeptidase that was recognized to suppress the phenotypes of the brassinosteroid receptor weak mutant bri1-5, which showed shorter primary inflorescence stem and secondary inflorescence branch length, compact rosette, and late flowering time [1]
We found that the lateral root (LR) number and LR branching density—defined as the number of emerged LRs per unit length of the root branching zone [32]—decreased significantly in bri1-5, they dramatically increased in two different BRS1 overexpression materials bri1-5 35S-BRS1 and bri1-5 brs1-1D compared with the bri1-5 mutant (Figure 1a,c)
These results indicated that BRS1 is involved in the LR development of brassinosteroid-related mutants
Summary
BRS1 (BRI1 Suppressor 1) is a serine carboxypeptidase that was recognized to suppress the phenotypes of the brassinosteroid receptor weak mutant bri, which showed shorter primary inflorescence stem and secondary inflorescence branch length, compact rosette, and late flowering time [1]. Lateral root primordia (LRP) originate from pericycle cells [18,19] and must break through the overlying endodermis, cortex, and epidermis before forming a new lateral root (LR). This process is termed LR emergence, and is critical for determining the LR growth rate and distribution [20]. XTR6/XTH23 and EXP17 control cell wall remodeling, and are dramatically increased in expression during LRP pass through the outer cells [24,29] These observations indicate that the extracellular space experiences considerable changes prior to LR emergence. We carefully investigated the effects of overexpressing BRS1 on LRs and found that BRS1 facilitates LR emergence, shedding new light on the process of LR emergence and the role of extracellular-localized SCPs
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