The chromatin remodelling factor BrCHR39 positively regulates apical dominance by auxin signalling in Brassica rapa

Chromatin remodelling complexes like the SHPRH (sucrose non-fermenting 2 (SNF2), histone linker, plant homeodomain (PHD), really interesting new gene (RING), and helicase domains) control gene expression via ATPase and nucleosome-E3 ubiquitin ligase activities. The members of SHPRH have been shown to play substantial roles in DNA repair in mammals, while their functions remain largely unknown in plants. In this study, we further investigated a SHPRH member designated as BrCHR39 in Brassica rapa, building on earlier experimental evidence from our laboratory that highlighted its functional significance. RNA interference (RNAi)-mediated knockdown of endogenous BrCHR39 expression, consistent with our prior findings, resulted in impaired apical dominance, semi-dwarfism, and enhanced axillary bud outgrowth in B. rapa. These results confirm and extend our earlier observations. The transgenic B. rapa lines had reduced cell numbers in parenchyma due to the affected cell division in the main stem. Suppression of BrCHR39 expression resulted in a significant decrease in the expression levels of auxin-related genes, and the application of exogenous auxin sufficiently restored the apical dominance in the silenced B. rapa lines. In addition, the silencing of BrCHR39 triggered a negative regulatory expression pattern in auxin-responsive genes. Furthermore, we demonstrated that BrCHR39 interacts with BrASK18 via its F-box domain, playing a critical role in the auxin signalling pathway. Taken all together, our study provides compelling evidence that BrCHR39 positively regulates apical dominance through auxin signalling in B. rapa.