An Anther-Specific Sugar Transporter SlSTP9 Is Modulated by SlDof12 to Regulate Anther Elongation and Reproductive Success in Tomato

Successful pollination in crops relies on the intricate coordination between the anther and the style. However, the role of sugar transporters in modulating floral architecture and influencing pollination success remains poorly understood. This study investigates the function and transcriptional regulation of the tomato sugar transporter, SlSTP9, using a combination of CRISPR/Cas9-mediated gene editing, yeast functional complementation, microscale thermophoresis, transcriptomic, and metabolic profiling. We identify SlSTP9 as an anther endothecium/middle-layer-specific sugar transporter localized to the plasma membrane. Loss of SlSTP9 function results in impaired endothecium and middle-layer cell expansion, leading to shortened anthers, premature dehiscence, stigma exsertion, and ultimately pollination failure. In contrast, overexpression of SlSTP9 enhances fruit set. Functional assays show that SlSTP9 exhibits high affinity for fructose and galactose, and its loss in the slstp9 mutant leads to excessive accumulation of galactose, activation of phenylpropanoid metabolism, and premature lignification of endothecium cells. Furthermore, we demonstrate that the Dof-family transcription factor SlDof12, which is also localized in the anther endothecium and middle layer, directly represses SlSTP9 expression. Overexpression of SlDof12 recapitulates the floral defects observed in the slstp9 mutant. These findings reveal a regulatory module involving SlDof12 and SlSTP9 that controls anther elongation by preventing premature lignification, highlighting a novel role for sugar transporters in shaping floral architecture and modulating reproductive success.