Genome-Wide Identification and Expression Analysis of WRKY Gene Family in Capsicum annuum L.

The WRKY family of transcription factors is one of the most important families of plant transcriptional regulators with members regulating multiple biological processes, especially in regulating defense against biotic and abiotic stresses. However, little information is available about WRKYs in pepper (Capsicum annuum L.). The recent release of completely assembled genome sequences of pepper allowed us to perform a genome-wide investigation for pepper WRKY proteins. In the present study, a total of 71 WRKY genes were identified in the pepper genome. According to structural features of their encoded proteins, the pepper WRKY genes (CaWRKY) were classified into three main groups, with the second group further divided into five subgroups. Genome mapping analysis revealed that CaWRKY were enriched on four chromosomes, especially on chromosome 1, and 15.5% of the family members were tandemly duplicated genes. A phylogenetic tree was constructed depending on WRKY domain' sequences derived from pepper and Arabidopsis. The expression of 21 selected CaWRKY genes in response to seven different biotic and abiotic stresses (salt, heat shock, drought, Phytophtora capsici, SA, MeJA, and ABA) was evaluated by quantitative RT-PCR; Some CaWRKYs were highly expressed and up-regulated by stress treatment. Our results will provide a platform for functional identification and molecular breeding studies of WRKY genes in pepper.

Cloning and characterization of the CarbcL gene related to chlorophyll in pepper (Capsicum annuum L.) under fruit shade stress.

Light is an important environmental factor for fruit development and ripening in pepper plant. Fruit bagging is a significant agrotechnology practiced for the illumination regulation of fruits; some previous researches have shown that fruit bagging could improve the appearance and external quality of fruits and cause them to mature early. However, it would decrease the intrinsic qualities of fruits; especially, fruit bagging could decrease the content of capsanthin in peppers. On the basis of these details, fruit bagging was used as the method of fruit shade stress in this study to explore the characteristics and molecular mechanisms of pepper fruit's color change under shade stress. By using cDNA-AFLP under fruit shading, a fragment related to fruit color was obtained. Next, the full-length coding sequence of the gene was cloned from the pepper fruits. Homologous gene alignment confirmed that the gene has high homology with the rbcL gene, named CarbcL. The function of the CarbcL gene was identified through virus-induced gene silencing (VIGS); it was found that the fruit color changed completely from green to red except for some residue of green fleck when CarbcL gene was silenced, and the green color of fruits had not fully faded in the control group and the empty vector group. The combine determination of chlorophyll content showed that CarbcL was involved in the metabolic control of chlorophyll in pepper fruits; subsequently, HPLC was used to determine the content of capsanthin in pepper fruit which the CarbcL gene was silencing, and it was also found that the content of capsanthin decreased appreciably. These results further confirmed that CarbcL gene was involved in the adjustment of chlorophyll and capsanthin.

Silencing of dehydrin CaDHN1 diminishes tolerance to multiple abiotic stresses in Capsicum annuum L.

KEY MESSAGE: We cloned a dehydrins gene CaDHN1 from pepper and the expression of CaDHN1 was markedly upregulated by cold, salt, osmotic stresses and salicylic acid (SA) treatment. Dehydrins (DHNs) are a subfamily of group 2 late embryogenesis-abundant (LEA) proteins that are thought to play an important role in enhancing abiotic stress tolerance in plants. In this study, a DHN EST (Expressed Sequence Tag) was obtained from 6 to 8 true leaves seedlings of pepper cv P70 (Capsicum annuum L.) by our laboratory. However, the DHN gene in pepper was not well characterized. According to this EST sequence, we isolated a DHN gene, designated as CaDHN1, and investigated the response and expression of this gene under various stresses. Our results indicated that CaDHN1 has the DHN-specific and conserved K- and S- domain and encodes 219 amino acids. Phylogenetic analysis showed that CaDHN1 belonged to the SKn subgroup. Tissue expression profile analysis revealed that CaDH N1 was expressed predominantly in fruits and flowers. The expression of CaDHN1 was markedly upregulated in response to cold, salt, osmotic stresses and salicylic acid (SA) treatment, but no significant change by abscisic acid (ABA) and heavy metals treatment. Loss of function of CaDHN1 using the virus-induced gene silencing (VIGS) technique led to decreased tolerance to cold-, salt- and osmotic-induced stresses. Overall, these results suggest that CaDHN1 plays an important role in regulating the abiotic stress resistance in pepper plants.