Exploring the function of MaPHO1 in starch degradation and its protein interactions in postharvest banana fruits

Banana is a quintessential fruit known for its starch conversion process. During development, substantial starch accumulates in banana fruit and subsequently undergoes rapid degradation, contributing to flavor development during postharvest ripening. However, the genes orchestrating this crucial starch degradation process have not been comprehensively studied thus far. Through temporal transcriptomic analysis, we screened 63 active genes that were actively expressed in association with starch degradation during the ripening of banana fruits. The results found that phosphorolytic enzymes primarily regulate starch degradation at the early to middle stages of fruit ripening and that hydrolytic enzymes significantly contribute to starch degradation at the later stage. The expression of Musa acuminata starch phosphorylase 1 (MaPHO1) was the highest at the early to middle stages of banana ripening, characterized by the insertion of an L80 domain. While MaPHO1 was predominately found in the chloroplast, MaPHO2 was localized to the cell membrane. Starch accumulation was significantly increased by transient attenuation of MaPHO1 expression, whereas a drastic reduction in starch content was triggered by transient overexpression of MaPHO1, affirming its functional role in banana fruit ripening. By constructing a co-expression network, 29 categories, including 74 proteins interacting with MaPHO1 were identified. Tripartite interactions between MaPHO1 and both glucan, water dikinase 1 (GWD1) and enolase 1 (ENO1) were revealed by further validation through yeast two-hybrid and glutathione-S-transferase pull-down analyses.