Abstract
BACKGROUND: Proteins harboring the SPX domain are crucial for the regulation of phosphate (Pi) homeostasis in plants. This study aimed to identify and analyze the entire SPX gene family within the cucumber genome. RESULTS: The cucumber genome encompassed 16 SPX domain-containing genes, which were distributed across six chromosomes and categorized into four distinct subfamilies: SPX, SPX-MFS, SPX-EXS and SPX-RING, based on their structure characteristics. Additionally, gene duplications and synteny analysis were conducted for CsSPXs, revealing that their promoter regions were enriched with a variety of hormone-responsive, biotic/abiotic stress and typical P1BS-related elements. Tissue expression profiling of CsSPX genes revealed that certain members were specifically expressed in particular organs, suggesting essential roles in cucumber growth and development. Under low Pi stress, CsSPX1 and CsSPX2 exhibited a particularly strong response to Pi starvation. It was observed that the cucumber cultivar Xintaimici displayed greater tolerance to low Pi compared to black-spined cucumber under low Pi stress conditions. Protein interaction networks for the 16 CsSPX proteins were predicted, and yeast two-hybrid assay revealed that CsPHR1 interacted with CsSPX2, CsSPX3, CsSPX4 and CsSPX5, implying their involvement in the Pi signaling pathway in conjunction with CsPHR1. CONCLUSION: This research lays the foundation for further exploration of the function of the CsSPX genes in response to low Pi stress and for elucidating the underlying mechanism.