Jiangsu Key Laboratory for Horticultural Crop Genetic Improvement/Institute of Vegetable, Jiangsu Academy of Agricultural Sciences, Nanjing 210014, China
Abstract：Phytosulfokine (PSK), a class of essential plant peptide hormones, plays critical roles in plant disease resistance and defense responses. To systematically dissect the functions of the PSK gene family in watermelon (Citrullus lanatus) defense responses, a genome-wide identification and bioinformatics analysis of ClPSKs were performed, followed by expression profile analysis during fruit development and upon Fusarium oxysporum f. sp. niveum infection. The results showed that 4 ClPSKs (Cla97C01G016930, Cla97C08G160340, Cla97C10G193065 and Cla97C10G202430) were identified in the watermelon genome, distributed across 3 watermelon chromosomes. The molecular weight of ClPSKs-encoded proteins ranged from 9.276 to 11.491 kD. All ClPSKs were acidic and unstable proteins, and they all contained PSK family conserved motifs. The phylogenetic tree analysis showed that watermelon ClPSKs clustered with AtPSKs from Arabidopsis thaliana, indicating high evolutionary conservation. Promoter cis-acting element analysis revealed that the stress responsive cis-elements and the plant hormone responsive cis-elements were enriched in the promoter sequence of watermelon PSKs gene, which providing a molecular basis for ClPSKs involvement in stress responses. Expression analysis showed that ClPSKs exhibited tissue-differential expression, with the highest levels in leaf tissues, followed by roots. Cla97C01G016930, Cla97C08G160340 and Cla97C10G193065 exhibited the highest expression levels at 10 d after pollination of watermelon fruit, indicating that these genes played a role in the early stage of watermelon fruit growth and development. Fusarium oxysporum infection significantly induced the expression of ClPSKs genes. Cla97C01G016930, Cla97C08G160340, and Cla97C10G193065 had the highest expression levels at 12 h after F. oxysporum f. sp. niveum infection, while Cla97C10G202430 showed continuous upregulation, indicating distinct spatiotemporal roles of ClPSKs in disease defense. This study provides scientific references for further understanding the role of ClPSKs in watermelon disease resistance and defense responses.
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