| Identification and analysis of the hot pepper germplasm resources was the basic of improving the breeding efficiency and quality of chili pepper. As the key quality characters, Capsaicinoids were the main source of spiciness, of which capsaicin and dihydrocapsaicin were the primary determinants and mainly synthesized in the epidermal cells’ vacuole of of fruits’ placenta. The contents were the the most important quality trait to assess quality characters of pepper. It had been widely used in many fields, however, the synthesis of natural capsaicinoids could not meet the market demand. Chemical regulation and genetic engineering methods were able to improve capsaicinoids contents economically and effectively. It also had great theoretical significance and practical value to the change rule of capsaicinoids and molecular mechanism of hot formation, especially for the biosynthetic regulatory mechanism. We first did the analysis on the Genetic Relationship of Twenty-two Pepper Cultivars, then we picked out the hottest one which called ’Guijiangwang’, the Indian pepper, was used to study the changes of capsaicin and dihydrocapsaicin contents at placenta tissue under the condition of exogenous hormone. Meanwhile, RNA-Seq was used to analyze expression profiling of putative genes involved in the biosynthesis of Capsaicin for five different developmental stages at fruits’placenta. The main results were included as follows:1. Analysis on the Genetic Relationship of twenty-two Pepper CultivarsEleven botanical characters of22pepper cultivars were investigated, and clustering analysis were applied. The results showed that the Coefficient of variation (CV) of11traits are13.75%to138.12%, the Max CV was single fruit weight, the min is stem diameter. the genetic distance of22pepper cultivars is1.036-7.618, all cultivars were clustered into four groups, the first group include11species, the second group include8species,’No8’ with a distant relationship with other species, singly clustered into the third group, the fourth group only contain two species.2. Effects of SA and MeJA on Capsaicinoids content of ’guijiaowang’’Guijiaowang’ was used to study the effect of the Salicylicacid(SA) and Methyl Jasmonate(MeJA) with different concentrations on capsaicin and dihydrocapsaicin content. Capsaicin and Dihydrocapsaicin contents were analysed by HPLC after SA and MeJA treatments at different concentrations. This study would provide a reference for the exogenous application of SA and MeJA on enchancement the contents of capsaicinoids.The results were as followed:(1) The treatment effects under different concentrations of SA and MeJA showed a consistent change tendency of capsaisin and dihydrocapsaisin in plasenta with control. The contents of capsaisin and dihydrocapsaisin increase firstly and reach peak at40day after anthesis, then decrease from40to50day after anthesis.(2) Under SA treatment, low concentrations (1.5mmol·L-1SA) were most conducive to the accumulation of capsaicin and dihydrocapsaicin, peak value up to98.400mg·g-1and5.771mg·g-1respectively. Relatively high SA levels (2.5mmol·L-1,3.5mmol·L-1,5.0mmol· L-1SA) significantly inhabit the accumulation of capsaisin and dihydrocapsaisin.(3) Under MeJA treatment, four out of five MeJA concentration level were beneficial to enhance capsaicin and dihydrocapsaicin content to different level. The maximum vaules reached to116.181mg·g-1and7.035mg·g-1of capsaisin and dihydrocapsaisin respectively at2.5mmo·L-1MeJA treatment.3. Analysis on gene expression profiling for genes related to spicy of "Guijiaowang"We did analysis according to gene expression profiling of10,20,30,40,50days after flowering on’Guijiaowang’fruit placenta with RNA-Seq and screening the related genes.We identified135known genes as candidates except two genes for enzymes in all known genes that related to capsaicin synthesis. We conjectured that10genes including CA01g32960, CA02g19270, CA01g32970, CA00g95510, CA05g20790, CA07g11150, CA03g35350,CA01g01120,CA04g10340, CA07g08100, presented a positive correlation. They play a crucial role in the regulation of capsaicin synthesis process and could be used to do further exploration as key genes. In addition, we identified20new candidate genes that related to capsaicin synthesis according to analysis of expression profiling at different developmental stages. These genes were all presented for the first time in the related synthesis of capsaicin. We also found two paths that regulated by CAD and GS which may had relationship with capsaicin synthesis and accumulation. It would futher improve the biosynthetic and degradative pathways of capsaicin. |
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