A Subsidiary Cell-Localized Glucose Transporter Promotes Stomatal Conductance and Photosynthesis.

It has long been recognized that stomatal movement modulates CO availability and as a consequence the photosynthetic rate of plants, and that this process is feedback-regulated by photoassimilates. However, the genetic components and mechanisms underlying this regulatory loop remain poorly understood, especially in monocot crop species. Here, we report the cloning and functional characterization of a maize () mutant named (). Map-based cloning of followed by confirmation with the clustered regularly interspaced short palindromic repeats (CRISPR)/ CRISPR system identified the causal mutation in a Clade I Sugars Will Eventually be Exported Transporters (SWEET) family gene, which leads to the E81K mutation in the CST1 protein. encodes a functional glucose transporter expressed in subsidiary cells, and the E81K mutation strongly impairs the oligomerization and glucose transporter activity of CST1. Mutation of results in reduced stomatal opening, carbon starvation, and early senescence in leaves, suggesting that functions as a positive regulator of stomatal opening. Moreover, expression is induced by carbon starvation and suppressed by photoassimilate accumulation. Our study thus defines as a missing link in the feedback-regulation of stomatal movement and photosynthesis by photoassimilates in maize.