D53 is a dual-function transcription repressor of strigolactone signaling in cotton

Strigolactones (SLs), a class of phytohormones, play a pivotal role in governing critical aspects of plant development, including shoot branching and root development. DWARF53 (D53) is a key repressor in the SL signaling. Nevertheless, its involvement and regulatory mechanisms in cotton fiber development—a representative single-cell model, has remained elusive. In this study, we unveil GhD53 represses the transcription of SL-inducible genes GhFAD3-2 and GhFAD3-4, which are involved in linolenic acid biosynthesis—a stimulant of cell elongation, thus inhibiting cotton fiber elongation. We demonstrate that GhD53's inhibitory influence on cotton fiber elongation is relieved in the presence of SLs, as GhD53 undergoes degradation. This alleviation of GhD53 repression triggers the activation of GhFAD3 expression, promoting fiber cell elongation. Remarkably, GhD53 serves as a dual-function transcription repressor, impeding SLs’ role in fiber elongation. Firstly, as a transcription factor, GhD53 directly binds to GhFAD3 promoters, suppressing their transcription. Secondly, GhD53 physically interacts with GhSLRF, a bHLH-type transcription factor, preventing it from binding to GhFAD3 promoters and repressing its transcription activation activity. GhD53 emerges as a pivotal component in the regulatory network governing SL signaling transduction. Overall, our findings provide novel insights into D53’s role in SL signaling and delineate a comprehensive framework for transmitting SL signals to modulate plant cell elongation behavior. Using an in vitro expressed transcription factor (TF) to probe bare genomic DNA fragments, in order to establish binding sites (peaks) and sequence motifs.