Role of GhMyoVIII2 in regulating the fruit branch angle revealed by integrated bioinformatic, expression, and VIGS analyses in upland cotton.

Fruit branch angle (FBA) is a key agronomic trait that affects cotton plant architecture and planting density and significantly influences yield and mechanical harvesting efficiency. Myosin VIII (MyoVIII), a plant-specific molecular motor protein, plays crucial roles in cell division, hormone homeostasis, and morphogenesis; however, its function in regulating FBA in cotton remains unclear. On the basis of findings from previous genome-wide association studies (GWAS), several GhMyosin-VIII genes (GhMyoVIIIs) that were significantly associated with FBA were identified in upland cotton. Bioinformatics analysis further demonstrated that GhMyoVIIIs are highly conserved across dicotyledons, with its promoter region being rich in cis-acting elements related to hormone response and growth development. Expression analysis revealed significantly elevated GhMyoVIII2 expression in cotton varieties with relatively large FBA. Following virus-induced gene silencing (VIGS) of GhMyoVIII2, significant reductions in FBA were observed during both the flowering and boll-setting stages, resulting in a more compact plant architecture. Physiological measurements further revealed markedly decreased levels of auxin (indole-3-acetic acid, IAA) and brassinosteroids (BRs) in the silenced plants, accompanied by the downregulation of genes involved in their biosynthetic pathways and the upregulation of genes associated with their degradation pathways. Additionally, multiple key genes associated with branching exhibited significant expression alterations. Taken together, these findings suggest that GhMyoVIII2 likely influences cotton FBA by regulating IAA and BR synthesis and signaling pathways, providing new genetic resources and a theoretical basis for improving cotton plant architecture.