The cross-talk of brassinosteroid signaling and strigolactone signaling during mesocotyl development in rice

The elongation of the mesocotyl is modulated by phytohormones, which have been shown to exert both synergistic and antagonistic influences on this process. However, the complex regulatory networks involved remain to be fully understood. To investigate the interplay between strigolactone (SL) and brassinosteroid (BR) signaling pathways in the regulation of mesocotyl elongation, we analyzed the elongation phenotypes of mutants deficient in SL and BR signaling. Our findings indicate that the SL signaling pathway operates downstream of the BR signaling pathway during mesocotyl elongation. Furthermore, a comprehensive analysis of genome-wide expression profiles in response to BR treatment demonstrated that BR signaling activation inhibits carotenoid biosynthesis, while the inhibition of SL signaling alters the mesocotyl's sensitivity to BR. This suggests a potential convergence of SL and BR pathways in regulating shared target genes during mesocotyl development. The results indicate that both SL and BR signaling pathways can influence mesocotyl elongation through the action of BBX6. These findings will enhance our understanding of the underlying mechanisms of mesocotyl development and provide valuable insights for the breeding elite rice varieties suitable for direct seeding.