Identification of Genes Responsive to Abiotic Stresses in Sweet Orange (Citrus sinensis L.) in the Protein Phosphatase 2C Gene Family

Protein phosphatase type 2C (PP2C) is a large multigene family responsible for transmitting cold, salinity, and drought signals in plant cells. Given the limited functional information on PP2C in sweet orange, this study aimed to identify and investigate the genome-wide distribution of the Citrus sinensis protein phosphatase 2C (CsPP2C) gene family in response to abiotic stresses. The results showed that the 62 identified PP2C proteins had molecular weights ranging from 25.9 to 119.9 kDa, isoelectric pH (pI) values spanning from acidic to alkaline, instability indices ranging from 30.80 to 66.37, aliphatic index from 43.68 to 100.11, and GRAVY values ranging from -0.543 to 0.067. According to the chromosomal distribution map, the highest number of genes was located on chromosome Ch1. Gene structure analysis revealed that approximately 34% of CsPP2C genes contained four exons, 24% had five exons, and 13% had six exons. The highest domain diversity was observed in the CsPP2C13 protein, while the highest number of motifs was found in CsPP2C14 and CsPP2C15. Phylogenetic analysis grouped the CsPP2C proteins and drought-related PP2C genes from Arabidopsis and rice into three distinct clades, with sweet orange drought stress proteins classified into clade III. The expression patterns of CsPP2Cs genes in response to drought stress varied significantly across different sweet orange organs, with the highest expression levels observed in seeds and flowers. The expression profile of CsPP2C37 is unique, making it a promising target for exploring the cellular mechanisms underlying drought stress tolerance.