Overexpression of 9-cis-Epoxycarotenoid Dioxygenase Gene, IbNCED1, Negatively Regulates Plant Height in Transgenic Sweet Potato.

Plant height is one of the key agronomic traits for improving the yield of sweet potato. Phytohormones, especially gibberellins (GAs), are crucial to regulate plant height. The enzyme 9-cis-epoxycarotenoid dioxygenase (NCED) is the key enzyme for abscisic acid (ABA) biosynthesis signalling in higher plants. However, its role in regulating plant height has not been reported to date. Here, we cloned a new NCED gene, IbNCED1, from the sweet potato cultivar Jishu26. This gene encoded the 587-amino acid polypeptide containing an NCED superfamily domain. The expression level of IbNCED1 was highest in the stem and the old tissues in the in vitro-grown and field-grown Jishu26, respectively. The expression of IbNCED1 was induced by ABA and GA3. Overexpression of IbNCED1 promoted the accumulation of ABA and inhibited the content of active GA3 and plant height and affected the expression levels of genes involved in the GA metabolic pathway. Exogenous application of GA3 could rescue the dwarf phenotype. In conclusion, we suggest that IbNCED1 regulates plant height and development by controlling the ABA and GA signalling pathways in transgenic sweet potato.

Genome-wide in silico identification and expression analysis of beta-galactosidase family members in sweetpotato [Ipomoea batatas (L.) Lam].

BACKGROUND: Sweetpotato (Ipomoea batatas (L.) Lam.) serves as an important food source for human beings. ß-galactosidase (bgal) is a glycosyl hydrolase involved in cell wall modification, which plays essential roles in plant development and environmental stress adaptation. However, the function of bgal genes in sweetpotato remains unclear. RESULTS: In this study, 17 ß-galactosidase genes (Ibbgal) were identified in sweetpotato, which were classified into seven subfamilies using interspecific phylogenetic and comparative analysis. The promoter regions of Ibbgals harbored several stress, hormone and light responsive cis-acting elements. Quantitative real-time PCR results displayed that Ibbgal genes had the distinct expression patterns across different tissues and varieties. Moreover, the expression profiles under various hormonal treatments, abiotic and biotic stresses were highly divergent in leaves and root. CONCLUSIONS: Taken together, these findings suggested that Ibbgals might play an important role in plant development and stress responses, which provided evidences for further study of bgal function and sweetpotato breeding.

Nitrogen utilization characteristics and early storage root development in nitrogen-tolerant and nitrogen-susceptible sweet potato.

In recent years, sweet potato has been cultivated not only in marginal lands but also in fertile plains in northern China. The fertile nitrogen (N)-rich soil may inhibit storage root formation. Cultivars with different N tolerances and split application of reduced N rates should be considered. To investigate the effects of N on the N utilization, root differentiation, and storage root formation of cultivars with different N tolerances, the cultivars Jishu26 (J26) and Xushu32 (X32) were treated with three N levels supplied by urea: 0 (N0), 200 (N1) and 400 mg kg-1 (N2). With increasing N rates, "X32" absorbed less N in plants and distributed more N to developing storage roots than "J26." The storage root development of "J26" was sensitive to both N1 and N2, while that of "X32" was only sensitive to N2. High N nutrition upregulated the expression of certain genes during storage root formation, such as PAL, CHI, F3H, C4 H, 4CL, CAD, α-amylase, and ß-amylase. Under N1 and N2, "X32" led to an increased sugar supply in sink organs and downregulated the expression of genes related to lignin and flavonoid synthesis, which promoted the C flux toward starch metabolism, thus reducing lignification and promoting starch accumulation during storage root formation. These results provide evidence for the effects of N on the C distribution in different metabolic pathways by regulating the expression of related key genes. N-tolerant cultivars are suitable in fertile plain areas because of the earlier formation of storage roots under high N conditions.

Differences between nitrogen-tolerant and nitrogen-susceptible sweetpotato cultivars in photosynthate distribution and transport under different nitrogen conditions.

To characterize the differences in photosynthate distribution and transport between nitrogen(N)-tolerant and N-susceptible sweetpotato cultivars under different N conditions, three N levels, including 0 (N0), 120 (N120), and 240 kg ha-1 (N240), were used in field experiments with the Jishu26 (J26) and Xushu32 (X32) cultivars in 2015 and 2016. The results from both years revealed that high N application reduced the tuberous root yield, the tuber/vine rate of carbon-13 (13C), and top-to-base (three equal segments of stem divided from the fifth opened leaf of the shoot tip to the main stem, defined as the top, middle, and base parts, respectively) gradients such as sucrose, ammonia N and potassium along the stem. 'J26' showed a higher yield than 'X32' under N0 but lower yield than 'X32' under N120 and N240. It also exhibited a higher 13C distribution to tuberous roots compared with that of 'X32' under N0, and the opposite trend was observed under N120 and N240. Under N0, 'J26' showed a steep top-to-base amino acid gradient and a significantly lower top-to-base sucrose increase along the stem in the late growth stage. Under N120 and N240, 'X32' exhibited a greater top-to-base decrease in the ammonia N along the stem during the main growth stages, a steep top-to-base sucrose gradient along the stem in the early growth stage, and a lower top-to-base sucrose increase along the stem in the middle and late growth stages. The formation of a reasonable photosynthate distribution structure attributed to high yield was related to a desirable sucrose, ammonia N or K+ gradient downward along the stem. These results might help provide farmers with sweetpotato cultivars using less or no N fertilizer in soils of different fertility and enhance the knowledge of yield-related physiology.