Functional characterization of Acyl-CoA Synthase 1 in tomato branch angle development

Branch angle is a crucial determinant of plant architecture, which is an important agronomic trait that contributes greatly to plant yield. In this study, we reported that SlACOS1 (Acyl-CoA synthase1) was related to regulate the branch angle in tomato (Solanum lycopersicum). Knockout of the SlACOS1 gene through CRISPR/Cas9 editing system resulted in a reduced lateral branch angle. Histological analysis revealed that editing SlACOS1 stimulated asymmetric growth of the branch base caused by the curve growth of vascular cylinder, parenchymatous tissue incrassation, cell elongation and expansion in abaxial side (AB) of the branch. Further analyses revealed that SlACOS1 responds to auxin and influenced its asymmetric distribution, leading to higher auxin concentration in the AB sides of the branch and subsequent differential growth of the two branch sides. In addition, SlACOS1 interacted with two lignin biosynthesis genes SlCCR5 and 6 to regulate lignin content in the branch. The Slacos1 mutants bent upward more rapidly than WT in the stem gravitropism assay. However, the amyloplast sedimentation rate of statolith cells showed no significant difference between Slacos1 and WT, suggesting SlACOS1 functions independently of gravity. In conclusion, the SlACOS1 contributed to asymmetric growth of branch to regulate the branch angle by modulating the asymmetric distribution of auxin and biosynthesis of lignin.