Cloning and Expression Analysis of Expansin Gene IbEXPA4 in Sweet Potato (Ipomoea batatas)
CAI Zhao-Qin1, WU Qiang1, CHEN Hui1, XIAO Dong1,2,*, WANG Ai-Qin1,2, HUANG Yong-Mei3, LI Hui-Feng3, ZHAN Jie1,2, HE Long-Fei1,2,*
1 National Demonstration Center for Experimental Plant Science Education/College of Agriculture, Nanning 530004, China; 2 Guangxi Key Laboratory for Agro-Environment and Agro-Product Safety, Nanning 530004, China; 3 Maize Research Institute of Guangxi Academy of Agricultural Sciences, Nanning 530007, China
Abstract：Plant expansin protein is a kind of plant cell wall protein, which plays an important role in plant growth and development. This group conducted transcriptome studies on the development of sweet potato (Ipomoea batatas) root tubers, and identified an expansin protein gene IbEXPA4 (Ipomoea batatas expansin-A4-like, IbEXPA4) that was significantly up-regulated in the middle period of expansion of sweet potato root tuber. The expansin protein gene IbEXPA4 were cloned and analyzed using sweet potato varieties 'Guijingshu 8' and 'Guizishu 1' as materials in this study. The results showed that the complete open reading frame of this gene contained 771 bp, encoding 256 amino acids. The sequence information of this gene was uploaded to NCBI (GenBank No. MW361490.1). Bioinformatics analysis showed that relative molecular weight of IbEXPA4 protein was 27.53 kD, theoretical isoelectric point was 8.8, instability coefficient was 37.96, average hydrophobicity was -0.117, and fat coefficient was 65.62, which indicated that IbEXPA4 protein was a stable hydrophilic protein. The prediction of secondary and tertiary structure showed that the protein mainly contained random curls. The structure of IbEXPA4 protein was analyzed, it showed that IbEXPA4 protein had a signal peptide at the N terminal without transmembrane domain, and contained 2 conserved domains, DPBB_1 and Pollen_allerg_1. Subcellular localization predicted its location in the cell wall. The phylogenetic tree analysis showed that the IbEXPA4 had the highest homology with the expansin-A4-like gene of Ipomoea triloba, which was 99.22%. Quantitative fluorescence PCR showed that IbEXPA4 was expressed in the root tuber of 'Guijingshu 8' and 'Guizishu 1', which showed a trend of increase at first and then decrease. Moreover, the expression levels of IbEXPA4 gene reached the highest in root tubers after 60 d of transplantation, which were 3.09 times and 9.23 times higher than those of the control group (fibrous roots of 20 d), respectively. Comparison and analysis of the expression changes of IbEXPA4 in the root tubers of the two varieties showed that the change of IbEXPA4 was more significant in 'Guizishu 1'. Agricultural character analysis showed that root tuber length of 'Guijingshu 8' were significantly higher than those of 'Guizishu 1', while the root diameter of 'Guizishu 1' was significantly higher than that of 'Guijingshu 8' after 60 and 90 d of transplantation. Correlation analysis showed that the expression of IbEXPA4 in root tuber were significantly positively correlated with root tuber diameter and root tuber length. These results indicated that IbEXPA4 promoted the longitudinal growth and transverse growth of root tuber, and participated in the regulation of sweet potato root tuber growth. This study provides a theoretical basis for elucidating the molecular mechanism of sweet potato root tuber growth.
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