Huoying Chen

Molecular cloning and characterization of anthocyanin biosynthesis genes in eggplant (Solanum melongena L.)

Eggplant is rich in anthocyanins, which are one of the important secondary metabolites and beneficial to human health. In this study, four anthocyanin biosynthesis genes, including chalcone synthase (SmCHS), chalcone isomerase (SmCHI), flavanone 3-hydroxylase (SmF3H) and dihydroflavonol 4-reductase (SmDFR), were isolated from eggplant. Their expression profiles were investigated along with other two structural genes (SmF3′5′H and SmANS) in different tissues, bagging, and low-temperature treatments. The highest expression levels were observed in peels except for SmF3H which was detected in stems, and SmF3H was also the exclusive gene that did not show correlation with anthocyanin content. Unlike purple peels of the control, the bagged fruits displayed white peels and had no anthocyanin accumulation, because of the expression of SmCHI, SmF3′5′H, SmDFR, and SmANS totally depended on light. As low temperature stimulates anthocyanin accumulation, all the six anthocyanin biosynthesis genes were up-regulated in cold stress experiment, and SmCHS increased most obviously. Moreover, early biosynthesis genes (SmCHS, SmCHI, and SmF3H) responded earlier than late biosynthesis genes (SmF3′5′H, SmDFR, and SmANS) under low temperature. Subcellular localization suggested that the enzymes encoded by the genes cloned in this study were all located in cytosol and nucleus. To further characterize the function, their ectopic expression in Arabidopsis was performed, and overexpression lines displayed higher anthocyanin accumulation in stems and siliques. The present study provides insight into anthocyanin biosynthesis in eggplant and may facilitate genetic engineering for improvement of the anthocyanin content in plants.

SSR Mapping of QTLs Conferring Cold Tolerance in an Interspecific Cross of Tomato

A population of 146 RILs (Recombinant Inbred Line) was derived from the cross between a cold-sensitive cultivated Solanum lycopersicum L. XF98-7 and a cold-tolerant wild Solanum pimpinellifolium LA2184. Relative germination ratio (RGR) and chilling index (CI) were used to evaluate the cold tolerance of the parental lines and RILs. It was found that the RGR and CI were significantly different between S. lycopersicum XF98-7 and S. pimpinellifolium LA2184 under cold treatment, indicating that wild species was more adapted to chilling temperature. The continuous and normal distribution of RGR and CI in RIL population suggested that the trait of cold tolerance was a typically quantitative trait controlled by multigenes. The molecular linkage map was constructed by using 120 simple-sequence repeat (SSR) markers, resulting in 15 linkage groups, with a total distance of 256.8 cM and average interval of 2.14 cM. Five QTLs controlling RGR and four QTLs for CI were detected with genetic contribution ranging from 0.95% to 19.55%. Thus, the nine QTLs will provide references for further fine position mapping for cold tolerance. The polymorphic markers could be used as a way of indirectly selecting the plant trait of interest and would promote developing new tomato variety by marker-assisted selection.

Bayesian analysis of interacting quantitative trait loci (QTL) for yield traits in tomato

An F 2 population derived from the hybrid of Lycopersicon esculentum Mill.XF98-7×Lycopersicon pimpinellifolium LA2184 was used for genome-wide linkage analysis for yield traits in tomato. The genetic map, spanning the tomato genome of 808.4 cM long was constructed with 112 SSR markers distributing on 16 linkage groups. Main and epistatic effect QTLs controlling first flower node, number of flowers per truss, fruit set percentage and fruit weight were located using Bayesian model selection method. A total of 20 significant main effect QTLs and 16 pairs of epistatic QTLs were identified on 16 linkage groups. The proportions of phenotypic variation explained by the detected QTLs ranged from 1.9 to 25.9% and from 0.00 to 17.4% for main-effect and epistatic QTLs, respectively. Most QTL effects were predictable from the parental phenotypes. Additionally, one QTL was found to be pleiotropic, governing simultaneously first flower node and number of flowers per truss.

Effects of low light on photosynthetic properties, antioxidant enzyme activity, and anthocyanin accumulation in purple pak-choi (Brassica campestris ssp. Chinensis Makino)

Anthocyanins are secondary metabolites that contribute to red, blue, and purple colors in plants and are affected by light, but the effects of low light on the physiological responses of purple pak-choi plant leaves are still unclear. In this study, purple pak-choi seedlings were exposed to low light by shading with white gauze and black shading in a phytotron. The responses in terms of photosynthetic properties, carbohydrate metabolism, antioxidant enzyme activity, anthocyanin biosynthetic enzyme activity, and the relative chlorophyll and anthocyanin content of leaves were measured. The results showed that chlorophyll b, intracellular CO2 content, stomatal conductance and antioxidant activities of guaiacol peroxidase, catalase and superoxide dismutase transiently increased in the shade treatments at 5 d. The malondialdehyde content also increased under low light stress, which damages plant cells. With the extension of shading time (at 15 d), the relative chlorophyll a, anthocyanin and soluble protein contents, net photosynthetic rate, transpiration rate, stomata conductance, antioxidant enzyme activities, and activities of four anthocyanin biosynthetic enzymes decreased significantly. Thus, at the early stage of low light treatment, the chlorophyll b content increased to improve photosynthesis. When the low light treatment was extended, antioxidant enzyme activity and the activity of anthocyanin biosynthesis enzymes were inhibited, causing the purple pak-choi seedlings to fade from purple to green. This study provides valuable information for further deciphering genetic mechanisms and improving agronomic traits in purple pak-choi under optimal light requirements.