Characterization And Genetics Of A Mutant With Tuberous Roots Of White Skin And Yellow Flesh From Purple-fleshed Sweet Potato

Sweet potato, with high-yield, adaptability and resistances ranks as the fifth crop after rice, wheat, corn and potato in China. Purple-fleshed sweet potato has high content of anthocyanins which act as natural pigment and has important medical functions.This paper focuses on the purple-fleshed sweet potato cultivar Zhezi 1 and its mutant Xinli with white skin and yellow flesh. The botanical characteristics, photosynthetic features, major agronomic traits, and expressions of genes associated with anthocyanin synthesis of Zhezi 1 and the Xinli were studied. Moerover the genetic identifications on the mutant Xinli were performed. The main findings are as follows:1. Compared to Zhezi 1, Xinli has such characters as sprouting earlier with brighter bud colour, biger stems with colour changing from purple to green, shorter internodes, fewer branche number, shorter plant height, tuber skin colour from purple to white and tuber flesh colour from purple to yellow.The leaf Pn-PAR response curves of Zhezi 1 and Xinli showed a similar quadratic relationship; The compensation points of Zhezi 1 and Xinli were 26μmol·m-2·s-1 and 30μmol·m-2s-1 respectively, while their light saturation point ware 1430μmol·m-2·s-1 and 1600μmol·m-2·s-1 respectively. Xinli was more tolerant to high intense light than Zhezi 1. The leaf Pn-CO2 response curves of Zhezi 1 and Xinli showed a similar quadratic relationship; The CO2 compensation points of Zhezi 1 and Xinli are 24μmol·mol-1 and 44μmol·mol-1 respectively, while their CO2 saturation point at 886μmol·mol-1 and 1154μmol·mol-1 respectively. Xinli was more tolerant to high CO2 than Zhezi 1. Pn diurnal variation of Zhezi 1 and Xinli showed a typical bimodal curve with a lunch break phenomenon.The content of hormone GA3 in stem of Xinli was significantly lower than that of Zhezi 1, which resulted in its stronge stems and shorter internodes. The content of Z in tuberous toots of Xinli is much higher than that of Zhezi 1, it might be associated with the tuberous root growth.The yield of Xinli was 2737 kg/667m2,45% higher than that of Zhezi 1. The average tuber number per was plant 5.1 pieces and the tuber weight per plant was 0.984kg. Their tuberous roots showed spindle shape.The total anthocyanin content of the tuberous roots of Zhezi 1 was significantly higher than Xinli and 8 kinds of anthocyanin were detected in tuberous roots of Zhezi 1 by HPLC, but none in tuberous roots of Xinli. Dry matter content, starch and soluble sugar content of tuberous roots of Xinli were higher than those of Zhezi 1, but the protein contents were contrary.2. The gene expression of transcription factor IbMYBl and structural genes such as CHS, CHI, F3H, DFR, ANS and 3GT related with anthocyanin synthesis in tuberous roots of Xinlin showed lower than Zhezi 1 in different degree by semi-quantitative RT-PCR.3. There were no differences in the numbers of chromosome between Zhezi 1 and Xinli by flow cytometry analysis. The full-length IbMYB1 including coding sequence of Zhezi 1 and Xinli were cloned and sequenced. Their full-length were both 1300 bases, with 99% identities each other, and with 99% to 100% identities with other IbMYB1 sequences in Genbank. there were two kinds of IbMYB1 gene:IbMYB1-1 and IbMYBl-2 in Zhezi 1, but there was only IbMYB1-1 in Xinli by PCR detection. Therefore, The mutant Xinli showed deletion of IbMYBl-2, and IbMYB1 could not be transcribed and translated, thus anthocyanin synthesis could not be synthesed.