Highly ABA-Induced 1 (HAI1)-Interacting Protein HIN1 and Drought Acclimation Enhanced Splicing Efficiency at Intron Retention Sites

Plant acclimation and productivity during drought involves multiple layers of gene regulation including pre-mRNA splicing and intron retention (IR). The protein phosphatase Highly ABA-Induced 1 (HAI1) affects drought phenotypes. A screen for HAI1 interacting proteins identified a protein of unknown function, HAI1 Interacting Protein 1 (HIN1). We found that HIN1 is a novel plant-specific RNA-binding protein that affects splicing of IR-prone introns during drought stress. HIN1 can be dephosphorylated by HAI1 and may also recruit HAI1 to dephosphorylate other splicing regulators. Thus, HAI1-HIN1 regulation is a new mechanism connecting stress signaling to pre-mRNA splicing and contributing to drought tolerance.