Protein Phosphatase OsPP2C55 Negatively Regulates Abscisic Acid Biosynthesis and Saline–Alkaline Tolerance in Rice

In rice (<i>Oryza sativa</i> L.), the short-chain dehydrogenase protein OsABA2 plays a crucial role in regulating abscisic acid (ABA) biosynthesis. However, little is known about the other proteins that interact with OsABA2 to regulate ABA biosynthesis. Using yeast two-hybrid screening, we identified a novel OsABA2 interacting protein OsPP2C55, which contains a serine/threonine phosphatase (family 2C) catalytic domain. The yeast two-hybrid (Y2H) assay and firefly luciferase complementary imaging (LCI) assay confirmed these interactions. Subsequent studies revealed that saline-alkaline stress significantly downregulated <i>OsPP2C55</i> gene expression. Meanwhile, we constructed <i>ospp2c55</i> CRISPR gene knockout (<i>ospp2c55</i>-KO) plants using Agrobacterium genetic transformation. Compared with wild-type plants, <i>ospp2c55</i>-KO plants under saline-alkaline stress exhibited significantly elevated OsABA2 protein levels, leading to substantial increases in ABA content. In addition, <i>ospp2c55</i>-KO plants demonstrated heightened sensitivity to ABA during seed germination. Moreover, <i>ospp2c55</i>-KO plants improved the survival rate and stress-related indices of rice seedlings under saline-alkaline stress, and upregulated the expression of genes related to adversity stress (<i>OsNCED1</i>, <i>OsNCED3</i>, <i>OsABA2</i>, <i>OsSODCc2</i>, and <i>OsCatB</i>). We found that <i>OsPP2C55</i> plays a negative regulatory role in ABA biosynthesis and saline-alkaline stress tolerance in rice.