Expression analysis of sporamin genes in response to flooding stress in two sweetpotato cultivars with contrasting flooding tolerance

초록

Sweetpotato [Ipomoea batatas (L.) Lam.] is an important food crop highly susceptible to flooding stress, a condition severely reducing storage root yield. Sporamin, the principal storage protein in sweetpotato storage roots, functions as a multifunctional protein with Kunitz-type trypsin inhibitor activity and antioxidant properties. Various biotic and abiotic stresses induce sporamin gene expression; however, its regulatory response under flooding stress remains underexplored. Therefore, this study aims to investigate the expression patterns of sporamin A and B group genes in the leaves of the flood-tolerant cultivar Yeonjami (YJM) and flood-sensitive cultivar Jeonmi (JM) under flooding stress. Heatmap analysis of RNA-seq data revealed distinct expression profiles of sporamin A and B group genes under flooding stress and clear differences between both cultivars. Gene Ontology (GO) enrichment analysis showed significant enrichment of both groups for protease inhibitor-related functions, including serine-type endopeptidase and Kunitztype trypsin inhibitor activities. Quantitative RT-PCR analysis showed that two sporamin A group genes were strongly induced under flooding in both cultivars, peaking at 12 h. However, gene expression declined markedly at 48 h in YJM but remained consistently elevated in JM throughout the flooding treatment period. Most sporamin B group genes showed consistently low expression levels in both cultivars. These findings provide the first evidence that sporamin genes are transcriptionally regulated in sweetpotato leaves in response to flooding stress, suggesting that transient, rather than prolonged, induction of sporamin A group genes is associated with flooding tolerance in sweetpotato.

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