Integrative Analysis of the Metabolome and Transcriptome of a Cultivated Pepper and Its Wild Progenitor Chiltepin (Capsicum annuum L. var. glabriusculum) Revealed the Loss of Pungency During Capsicum Domestication

Pungency is a unique characteristic of chili peppers (Capsicum spp.) caused by capsaicinoids. The evolutionary emergence of pungency is thought to be a derived trait within the genus Capsicum. However, it is not well-known how pungency has varied during Capsicum domestication and specialization. In this study, we applied a comparative metabolomics along with transcriptomics analysis to assess various changes between two peppers (a mildly pungent cultivated pepper BB3 and its hot progenitor chiltepin) at four stages of fruit development, focusing on pungency variation. A total of 558 metabolites were detected in two peppers. In comparison with chiltepin, capsaicinoid accumulation in BB3 was almost negligible at the early stage. Next, 412 DEGs associated with the capsaicinoid accumulation pathway were identified through coexpression analysis, of which 18 genes (14 TFs, 3 CBGs, and 1 UGT) were deemed key regulators due to their high coefficients. Based on these data, we speculated that downregulation of these hub genes during the early fruit developmental stage leads to a loss in pungency during Capsicum domestication (from chiltepin to BB3). Of note, a putative UDP-glycosyltransferase, GT86A1, is thought to affect the stabilization of capsaicinoids. Our results lay the foundation for further research on the genetic diversity of pungency traits during Capsicum domestication and specialization.

Pepper Fruit Elongation Is Controlled by Capsicum annuum Ovate Family Protein 20

Fruit shape is one of the most important quality traits of pepper (Capsicum spp.) and is used as a major attribute for the classification of fruit types. Wide natural variation in fruit shape exists among the major cultivated species Capsicum annuum, allowing the identification of several QTLs controlling the trait. However, to date, no genes underlying fruit shape QTLs have been conclusively identified, nor has their function been verified in pepper. We constructed a mapping population from a cross of round- and elongated-fruited C. annuum parents and identified a single major QTL on chromosome 10, termed fs10, explaining 68 and 70% of the phenotypic variation for fruit shape index and for distal fruit end angle, respectively. The QTL was mapped in several generations and was localized to a 5 Mbp region containing the ortholog of SlOFP20 that suppresses fruit elongation in tomato. Virus-induced gene silencing of the pepper ortholog CaOFP20 resulted in increased fruit elongation on two independent backgrounds. Furthermore, CaOFP20 exhibited differential expression in fs10 near-isogenic lines, as well as in an association panel of elongated- and round-fruited accessions. A 42-bp deletion in the upstream region of CaOFP20 was most strongly associated with fruit shape variation within the locus. Histological observations in ovaries and fruit pericarps indicated that fs10 exerts its effect on fruit elongation by controlling cell expansion and replication. Our results indicate that CaOFP20 functions as a suppressor of fruit elongation in C. annuum and is the most likely candidate gene underlying fs10.

Seed treatment using rhizobacteria as plant growth promotion of two chili variety (Capsicum annuum L.)

The research aims to find out the effect of pre-germination treatment seeds using rhizobacteria as plant growth promotion of two varieties of red chili peppers in the field. The experiment used a randomized design of factorial groups. Factors studied were varieties (V) and rhizobacteria types (R). The variety factor consists of 2 varieties namely PM999 (V1) and Kiyo F1 (V2). While the type of rhizobacteria factor tried consists of 8 treatment, namely, control (R0), Azotobacter sp. (R1), B. megaterium (R2), P. atmuta (R3), B. alvei (R4), Flavobacterium sp. (R5), B. coagulans (R6), B. firmus (R7) and B. pilymixa (Rs). Each treatment was repeated 3 times, so there were 48 experimental units. Each unit of experiment is represented by 5 sample plants. The data was analyzed using ANOVA and continued with DMRT test at real level α = 0.05. The results showed that vegetative growth and production of chili plants until the age of 45 days after planting in each variety is not dependent on the pre-germination treatment of seeds with rhizobacteria. But the varieties of chili plants used affect vegetative growth and production. PM999 varieties are superior to the Kiyo F1 variety. Pre-germination treatment of seeds using rhizobacteria is relatively effective in improving vegetative growth and yield of chili plants. Among the 8 isolates rizobacteria isolate Azotobacter sp., B. megaterium, B. coagulants, Flavobacterium sp., and P. atmuta relatively effective to provide an increased effect on the growth and production of chili plants.