Expression of sweet potato asparaginyl endopeptidase caused altered phenotypic characteristics in transgenic Arabidopsis

We have previously isolated an asparaginyl endopeptidase, SPAE, from senescent leaves of sweet potato (Ipomoea batatas cv. Tainong 57). Gene expression of SPAE was activated and enhanced in natural and induced senescent leaves (Chen et al., 2004). In this report the full-length SPAE cDNA was constructed in the T-DNA portion of recombinant pBI121 vector under the control of CaMV 35S promoter and transferred to Arabidopsis with Agrobacterium-mediated floral dip transformation. Three transgenic Arabidopsis plants were isolated and confirmed by kanamycin-resistance and genomic PCR amplification of SPAE. Protein gel blot also demonstrated sweet potato SPAE expression in these transgenic plants. Phenotypic analysis showed that transgenic plants exhibited earlier floral transition from vegetative growth and leaf senescence than control. Transgenic plants also contained fewer siliques and a higher percentage of incompletely-developed siliques per plant than control. Based on these results we conclude that sweet potato asparaginyl endopeptidase, SPAE, may function in association with the senescence process, and its expression enhances or promotes senescence in transgenic Arabidopsis plants. The altered phenotypic characteristics in transgenic plants with SPAE gene expression were also discussed.