SnRK2.6 phosphorylates sucrose transporter ZmSUT1 to enhance yield by modulating leaf senescence in maize

The extended stay-green trait is beneficial to increase photosynthetic efficiency, thereby enhancing crop yield. However, factors and mechanisms affecting this process remain largely unknown. Here, we cloned a leaf precocious senescence gene (lps1-1) and created additional null alleles. All lps1 mutants exhibited accelerated leaf senescence with reduced chlorophyll contents and photosynthetic efficiency. The 100-kernel weight and storage reserve content were decreased in lps1 kernels, while the opposite was observed in overexpression lines. Lps1 encoded a protein kinase SnRK2.6 that phosphorylated the sucrose transporter ZmSUT1 in the BETL region, thereby enhancing protein stability, homodimer formation ability, and sucrose transport activity. Overexpression of ZmSUT1 delayed leaf senescence and enhanced photosynthetic capacity and kernel weight, while mutation of ZmSUT1 did the opposite. This mechanism appears to be conserved in grasses. Our findings provide insights for yield and quality improvement in crops through delaying leaf senescence.