Ectopic Expression of Sweet Potato Cysteine Protease SPCP3 Alters Phenotypic Traits and Enhances Drought Stress Sensitivity in Transgenic Arabidopsis Plants

In this report sweet potato cysteine protease SPCP3 cDNAs, with or without the corresponding granulin-like domain, were overexpressed in transgenic Arabidopsis plants. Transgenic Arabidopsis plants with ectopic expression of full-length SPCP3 exhibited slight promotion of earlier floral transition from vegetative to reproductive growth and a higher percentage of yellowing siliques per plant. Transgenic progeny seeds showed similar patterns of germination rates and germination curves but lower germination percentages compared to those of wild-type control seeds. During drought treatment, photochemical Fv/Fm values and relative water content of transgenic plants were significantly reduced compared to those of wild-type controls. Transgenic Arabidopsis plants with ectopic expression of sweet potato SPCP3 with or without the corresponding C-terminal granulin-like domain exhibited similar drought-stress sensitivity patterns. Drought stress also enhanced SPCP3 gene expression, photochemical Fv/Fm reduction, and wilting in sweet potato detached leaves. Based on these data, we conclude that sweet potato granulin-containing cysteine protease SPCP3 is a functional gene, and its ectopic expression alters phenotypic traits and enhances drought-stress sensitivity in transgenic Arabidopsis plants. The presence of the C-terminal granulin-like domain has no significant influence on SPCP3-mediated drought-stress sensitivity in transgenic Arabidopsis plants.