Sugar-gibberellin crosstalk mediates leaf elongation in rice (Oryza sativa L.)

Leaf morphology and function influence the production and yield of photosynthetic carbohydrates, while leaf development requires an ample supply of energy and carbohydrates, regulated by sucrose transport proteins (OsSUTs). Loss of function mutation in OsSUTs lead to shortened leaves in rice; however, the underlying regulatory mechanism remains unclear. In this study, we investigated the growing leaves of ossut mutants, focusing on agronomic traits, leaf morphology and physiology, to determine the relationship between OsSUTs and leaf elongation. Results showed that the cell length in ossut mutants was significantly shortened, especially in the ossut3;5 lines. Chlorophyll content, net photosynthetic rate, sucrose exudation rate, and sucrose phosphate synthase activity in source leaves were also significantly decreased in ossut3;5. These findings suggest that inhibited sucrose transport in ossut mutants caused overaccumulation of sucrose and starch in source leaves, consequently blocking sugar export to the growing sink leaves. Additionally, mutations in OsSUTs affected leaf gibberellin (GA) content. Transcriptome analysis revealed that changes in the expression of genes related to GA biosynthesis, degradation, and signaling were the main causes of decreased GA levels in leaves. Furthermore, exogenous application of GA to rice leaves significantly increased both leaf and leaf cell lengths in all lines, whereas treatment with the GA synthesis inhibitor paclobutrazol (PAC) had the opposite effects. These results imply that the crosstalk between sucrose and GA potentially regulates rice leaf elongation.