Evolutionary Characteristics of the Rice SnRK2 Family and ABI5 Interaction Analysis Reveal Their Key Regulatory Role in Osmotic Stress Signaling
The ABA signaling pathway plays a central role in the regulation of plant responses to stress, with ABI5 serving as an important transcription factor within this pathway and exerting a key regulatory function. However, upstream kinases that regulate ABI5 have not been fully elucidated, especially the specific relationship between ABI5 and SnRK2 members in rice. Rice contains ten OsSAPK family members, which are classified into three conserved phylogenetic groups, including Group I (OsSAPK1/2/3), Group II (OsSAPK4/5/6/7), and Group III (OsSAPK8/9/10). This study aims to identify potential OsABI5-interacting kinases involved in ABA-mediated salt stress responses in rice. Phylogenetic analysis confirmed that the ten OsSAPKs were distributed into three conserved groups. Phenotypic analysis showed that ABA pretreatment alleviated salt-induced growth inhibition in rice seedlings, while RT-qPCR analysis revealed increased transcript levels of several OsSAPKs following ABA pretreatment under salt stress. Promoter analysis identified multiple hormone-responsive cis-elements in OsSAPK promoters, consistent with their transcriptional responses to ABA treatment. Integrated protein–protein interaction analyses revealed that OsSAPK1/3/4/9 physically bind to OsABI5, as demonstrated by complementary in vitro and in vivo assays. These findings identify four candidate OsABI5-interacting kinases and reveal potential SnRK2–ABI5 regulatory mechanisms in ABA-mediated salt stress responses.