Genome-wide analysis of the major latex protein gene family in papaya and the molecular basis of family member CpMLP14 in negatively regulating postharvest anthracnose resistance

Postharvest anthracnose is a critical disease affecting the quality of papaya fruit and the development of the papaya industry. However, the molecular mechanisms influencing this disease remain unclear. Since major latex proteins (MLPs) are pivotal components in the defensive responses of many plants, it is worthwhile to explore the functions and regulatory mechanisms of MLPs in papaya anthracnose resistance. In this paper, we performed a comprehensive genome-wide analysis of the papaya MLP gene family, identifying a total of 15 CpMLPs and providing information on their gene structures, protein motifs, phylogenetic relationships, and stress-related cis -regulatory elements. Based on bioinformatics and previous findings, CpMLP14 was selected for in-depth functional investigation. CpMLP14 was inhibited by the infection of Colletotrichum brevisporum , and CpMLP14 protein localized in nucleus and cytoplasm. Through transient overexpression of CpMLP14 in papaya, and heterologous expression CpMLP14 in tomato, as well as inoculation and phenotypic analysis, it was found that CpMLP14 negatively regulates papaya resistance to C. brevisporum . Further results demonstrated that CpMLP14 can inhibit the accumulation of reactive oxygen species (ROS) as well as the expression of pathogenesis related 1 ( PR1 ) and PR4 genes. Additionally, our results revealed that CpMLP14 was regulated by the transcription factor CpWRKY50, which has been proven to be a key transcription factor positively regulating papaya’s resistance to anthracnose. CpWRKY50 could directly bind to the W-box motif in the promoter of CpMLP14 and inhibit its expression. Collectively, these results provide a systematic understanding of the papaya MLP gene family, establish CpMLP14 as a direct target of CpWRKY50, and highlight the critical role of the CpWRKY50-CpMLP14 module in modulating papaya resistance against anthracnose. These results lay a foundation for future genetic improvement of disease resistance in papaya.