Pigment Biosynthesis and Molecular Genetics of Fruit Color in Pepper.

Pepper, as a vegetable crop with a wide cultivation area worldwide, besides being a significant condiment and food, also has a momentous use for chemistry, medicine, and other industries. Pepper fruits are rich in various pigments, such as chlorophyll, carotenoids, anthocyanins, and capsanthin, which have important healthcare and economic value. Since various pigments are continuously metabolized during the development of pepper fruits, peppers exhibit an abundant fruit-colored phenotype in both the mature and immature periods. In recent years, great progress has been made in the study of pepper fruit color development, but the developmental mechanisms are still unclear systematically dissected in terms of pigment, biosynthesis, and regulatory genes. The article outlines the biosynthetic pathways of three important pigments: chlorophyll, anthocyanin, and carotenoid in pepper and the various enzymes involved in these pathways. The genetics and molecular regulation mechanisms of different fruit colors in immature and mature peppers were also systematically described. The objective of this review is to provide insights into the molecular mechanisms of pigments biosynthesis in pepper. This information will provide theoretical basis for the breeding of high-quality colored pepper varieties in the future.

Genome-wide characterization of ascorbate peroxidase gene family in pepper (Capsicum annuum L.) in response to multiple abiotic stresses.

Pepper is widely grown all over the world, so it faces many abiotic stresses, such as drought, high temperature, low temperature, salt damage, and so on. Stresses causing the accumulation of reactive oxidative species (ROS) in plants are removed by antioxidant defense systems, and ascorbate peroxidase (APX) is an important antioxidant enzyme. Therefore, the present study performed genome-wide identification of the APX gene family in pepper. We identified nine members of the APX gene family in the pepper genome according to the APX proteins' conserved domain in Arabidopsis thaliana. The physicochemical property analysis showed that CaAPX3 had the longest protein sequence and the largest molecular weight of all genes, while CaAPX9 had the shortest protein sequence and the smallest MW. The gene structure analysis showed that CaAPXs were composed of seven to 10 introns. The CaAPX genes were divided into four groups. The APX genes of groups I and IV were localized in the peroxisomes and chloroplasts, respectively; the group II genes were localized in the chloroplasts and mitochondria; and the group III genes were located in the cytoplasm and extracell. The conservative motif analysis showed that all APX genes in the pepper had motif 2, motif 3, and motif 5. The APX gene family members were distributed on five chromosomes (Chr. 2, 4, 6, 8, and 9). The cis-acting element analysis showed that most CaAPX genes contain a variety of cis-elements related to plant hormones and abiotic stress. RNA-seq expression analysis showed that the expression patterns of nine APXs were different in vegetative and reproductive organs at different growth and development stages. In addition, the qRT-PCR analysis of the CaAPX genes revealed significant differential expression in response to high temperature, low temperature, and salinity stresses in leaf tissue. In conclusion, our study identified the APX gene family members in the pepper and predicted the functions of this gene family, which would provide resources for further functional characterization of CaAPX genes.

Mutations and Overexpression of CYP51 Associated with DMI-Resistance in Colletotrichum gloeosporioides from Chili.

Chili anthracnose caused by Colletotrichum spp. is an annual production concern for growers in China. Sterol C14-demethylation inhibitors (DMIs, such as tebuconazole) have been widely used to control this disease for more than three decades. In the current study, of 48 isolates collected from commercial chili farms in Jiangsu Province of China during 2018 and 2019, 8 single-spore isolates were identified as Colletotrichum gloeosporioides and the rest were identified as C. acutatum. To determine whether the DMI resistance of isolates develops in the field, mycelial growth of the 48 isolates was measured in culture medium with and without tebuconazole. In all, 6 of the 8 C. gloeosporioides isolates were resistant to tebuconazole, but all 40 of the C. acutatum isolates were sensitive to tebuconazole. The fitness cost of resistance was low based on a comparison of fitness parameters between the sensitive and resistant isolates of C. gloeosporioides. Positive cross-resistance was observed between tebuconazole and difenconazole or propiconazole, but not prochloraz. Alignment results of the CgCYP51 amino acid sequences from the sensitive and resistant isolates indicated that mutations can be divided into three genotypes. Genotype I possessed four substitutions (V18F, L58V, S175P, and P341A) at the CgCYP51A gene but no substitutions at CgCYP51B, while genotype II had five substitutions (L58V, S175P, A340S, T379A, and N476T) at CgCYP51A, concomitant with three substitutions (D121N, T132A, and F391Y) at CgCYP51B. In addition, genotype III contained two substitutions (L58V and S175P) at CgCYP51A, concomitant with one substitution (T262A) at CgCYP51B. Molecular docking models illustrated that the affinity of tebuconazole to the binding site of the CgCYP51 protein from the resistant isolates was decreased when compared with binding site affinity of the sensitive isolates. Our findings provide not only novel insights into understanding the resistance mechanism to DMIs, but also some important references for resistance management of C. gloeosporioides on chili.

Analysis of the ASMT Gene Family in Pepper (Capsicum annuum L.): Identification, Phylogeny, and Expression Profiles.

Acetylserotonin methyltransferase (ASMT) in plant species, one of the most important enzymes in melatonin biosynthesis, plays a rate-limiting role in the melatonin production. In this study, based on the whole genome sequence, we performed a systematic analysis for the ASMT gene family in pepper (Capsicum annuum L.) and analyzed their expression profiles during growth and development, as well as abiotic stresses. The results showed that at least 16 CaASMT genes were identified in the pepper genome. Phylogenetic analyses of all the CaASMTs were divided into three groups (group I, group II, and group III) with a high bootstrap value. Through the online MEME tool, six distinct motifs (motif 1 to motif 6) were identified. Chromosome location found that most CaASMT genes were mapped in the distal ends of the pepper chromosomes. In addition, RNA-seq analysis revealed that, during the vegetative and reproductive development, the difference in abundance and distinct expression patterns of these CaASMT genes suggests different functions. The qRT-PCR analysis showed that high abundance of CaASMT03, CaASMT04, and CaASMT06 occurred in mature green fruit and mature red fruit. Finally, using RNA-seq and qRT-PCR technology, we also found that several CaASMT genes were induced under abiotic stress conditions. The results will not only contribute to elucidate the evolutionary relationship of ASMT genes but also ascertain the biological function in pepper plant response to abiotic stresses.

Molecular characterization of two important antifungal proteins isolated by downy mildew infection in non-heading Chinese cabbage.

Two cDNA clones for a pathogen induced genes in non-heading Chinese cabbage (Brassica rapa ssp. chinensis L. cv. Suzhouqing) were isolated and characterized. The two full-length cDNA clones, designated Bcchi and BcAF were isolated during the resistance response to Peronospora parasitica. Sequence analysis of corresponding cDNA clones confirmed the translation products of both genes showed high degree of homology to other plant chitinases and plant defensins, respectively. Genomic DNA Southern blot analysis indicated that each gene represented a small multi-gene family. Upon inoculation with P. parasitica, both genes transcripts were rapid accumulated in the infected leaves. Tissue-specific expression of both genes showed that 24 h post-inoculation the highest expression tissue of Bcchi mRNA was leaves, and 12 h post-inoculation the highest expression tissue of BcAF mRNA was leaves. These data revealed that both genes may be involved in plant resistance against fungal pathogen infection.