The contents of carotenoids in the storage root of sweetpotato, Ipomoea batatas (L.) Lam. vary dramatically among different cultivars. However, so far little is known about the regulation of carotenoids synthesis in sweetpotato. In our laboratory, we identified a novel sweetpotato mutant, Nongdafu 14, which is a homogenous mutant derived from the wild type Kokei No. 14. The contents of carotenoids in the storage root of Nongdafu 14 were analyzed using high performance liquid chromatography (HPLC), and it was found that the amount of carotenoids, b-carotene, lutein and zeaxantion, three major types of carotenoids in sweetpotato storage roots, increased 2-26 folds in Nongdafu 14 compared to Kokei No. 14. Suppression subtractive hybridization (SSH) was used to identify genes that were differentially expressed in Nongdafu 14, and a differentially expressed cDNA library was constructed using the cDNA of Nongdafu 14 storage roots as tester and that of Kokei No. 14 storage roots as driver. Out of the 1 530 clones sequenced, we identified 292 nonredundant ESTs. GO and KEGG analyses of these differentially expressed ESTs indicated that diverse metabolism pathways were affected and candidate genes involved in regulation of carotenoids synthesis are suggested.

Iron-sulfur cluster biosynthesis involving the nitrogen fixation (Nif) proteins has been proposed as a general mechanism acting in various organisms. NifU-like protein may play an important role in protecting plants against abiotic and biotic stresses. Based on the EST sequence selected from salt-stressed suppression subtractive hybridization (SSH) cDNA library constructed with a salt-tolerant mutant LM79, a NFU gene, termed IbNFU1, was cloned from sweetpotato (Ipomoea batatas (L.) Lam.) via rapid amplification of cDNA ends (RACE). The cDNA sequence of 1 117 bp contained an 846 bp open reading frame encoding a 281 amino acids polypeptide with a molecular weight of 30.5 kDa and an isoelectric point (pI) of 5.12. IbNFU1 gene contained a conserved Cys-X-X-Cys motif in C-terminal of the iron-sulfur cluster domain. The deduced amino acid sequence had 66.08 to 71.99% sequence identity to NFU genes reported in Arabidopsis thaliana, Eucalyptus grandis and Vitis vinifera. Real-time quantitative PCR analysis revealed that the expression level of IbNFU1 gene was significantly higher in the roots of the mutant LM79 compared to the wild-type Lizixiang. Transgenic tobacco (cv. Wisconsin 38) plants expressing IbNFU1 gene exhibited significantly higher salt tolerance compared to the untransformed control plants. It is proposed that IbNFU1 gene has an important function for salt tolerance of plants.

AFLP fingerprinting of the 98 main sweetpotato varieties planted in China has been constructed. Using 17 AFLP primer combinations which were selected from 1 208 primer combinations and generated the most amounts of polymorphic bands, AFLP analysis of the 98 main sweetpotato varieties gave a total of 410 clear polymorphic bands with an average of 24.12 polymorphic bands per primer combination. Each one of the 98 sweetpotato varieties could be clearly distinguished by EcoR I-cta/Mse I-ggc primer combination which generated the most polymorphic bands. AFLP-based genetic distance ranged from 0.0546 to 0.5709 with an average of 0.3799. The dendrogram based on AFLP markers indicated that sweetpotato varieties coming from the same regions or having same parents were clustered in the same groups. Analysis of molecular variance (AMOVA) revealed greater variations within regions (94.08%) than among regions (5.92%). Thus, the genetic variations mainly existed within regions, while the variations among regions were very low in the tested sweetpotato varieties. Significant genetic variations existed between “Northern” and “Southern” sweetpotato varieties when Yangtze River was used as the dividing line.