ZmSKIP enhances drought tolerance by reducing stomatal aperture in maize

SKI-INTERACTING PROTEINS (SKIPs), primarily known as splicing factors, control gene expression at the post-transcriptional level in stress responses in plants. However, little is known about SKIPs in regulating plant drought stress at the transcriptional level, particularly in maize (Zea mays L.). Here, we discover that ZmSKIP enhances drought tolerance in maize. ZmSKIP transgenic plants were generated to study how ZmSKIP positively regulates drought tolerance. Overexpression of ZmSKIP promoted stomatal closure and reduced water loss, whereas the opposite effect was observed in skip-aa mutants. ZmSKIP directly binds to the "TAATA" motif in the promoter of B-cell lymphoma 2-associated athanogene 8 (ZmBAG8). bag8 mutants exhibit the decreased water loss and reduced stomatal aperture phenotype under drought stress. Additionally, ZmSKIP can be recruited by ZmBAG8 in stress granules (SGs) to decrease its protein abundance in the nucleus. Increased ZmBAG8 expression leads to larger stomatal aperture and normal plant growth. Under drought stress, the interaction between ZmSKIP and ZmBAG8 was abolished, while ZmSnRK2.3 phosphorylates ZmSKIP at Ser236 and Ser244 to enhances drought tolerance by strengthening the ability of ZmSKIP to suppress ZmBAG8 expression. Thus, our findings demonstrate that ZmSnRK2.3-mediated phosphorylation of ZmSKIP reduces ZmBAG8 expression and stomatal aperture, thereby enhancing drought tolerance in maize.