|Title: Functional characterization of a vegetative MADS-box gene, IbMADS1, during tuberous root formation in sweet potato (Ipomoea batatas)
M.S. student: Amy Ku
Advisor: Prof. Kai-Wun Yeh
Tuberization is an important stage during plant growth and development, especially in tuber crops. As an example, sweet potato (Ipomoea batatas) is characterized with fleshy tuberous roots for nutrient storage. Factors directing the induction of early tuberization have been investigated for a long time in sweet potato. At a glance of the molecular mechanism, we identified a tuberization-associated gene fragment through the cDNA-AFLP differential study. Derived cDNA was then named as Ipomoea batatas MADS-box 1 gene (IbMADS1), encoding 218 amino acids. Based on sequence alignment and phylogenic analysis, IbMADS1 exhibited a typical type II-MIKC structure, including two conserve domains, MADS-box and K-box. In phylogenetic study, IbMADS1 was grouped together with other orphan group MADS-box genes, such as AGL17 (Agamous-like 17) in Arabidopsis. Several IbMADS1 homologues were examined by Southern and Northern analyses among tuber-deficient Ipomoea relatives of sweet potato to investigate the evolutionary relationship in tuber formation. After further dissecting the IbMADS1 expression pattern in sweet potato, RNA transcripts were specifically detectable in roots, and the increase of IbMADS1 transcripts was correlated with early enlargement of tuberous roots. Overexpression assay was conducted in Potato (Solanum tuberosum) and sweet potato. Interestingly, tuberous swelling along roots was observed in some transgenic potato plants in addition to tuber formation from stems. Conclusively, we propose a hypothesis to illustrate the mechanism by which IbMADS1 participates in the initiation of tuberization in sweet potato.
Keywords: Ipomoea species－MADS-box genes－sweet potato－transcription factors－tuberization－vegetative expression