Characterization of Plant Homeodomain Transcription Factor Genes Involved in Flower Development and Multiple Abiotic Stress Response in Pepper.

Plant homeodomain (PHD) transcription factor genes are involved in plant development and in a plant's response to stress. However, there are few reports about this gene family in peppers (Capsicum annuum L.). In this study, the pepper inbred line "Zunla-1" was used as the reference genome, and a total of 43 PHD genes were identified, and systematic analysis was performed to study the chromosomal location, evolutionary relationship, gene structure, domains, and upstream cis-regulatory elements of the CaPHD genes. The fewest CaPHD genes were located on chromosome 4, while the most were on chromosome 3. Genes with similar gene structures and domains were clustered together. Expression analysis showed that the expression of CaPHD genes was quite different in different tissues and in response to various stress treatments. The expression of CaPHD17 was different in the early stage of flower bud development in the near-isogenic cytoplasmic male-sterile inbred and the maintainer inbred lines. It is speculated that this gene is involved in the development of male sterility in pepper. CaPHD37 was significantly upregulated in leaves and roots after heat stress, and it is speculated that CaPHD37 plays an important role in tolerating heat stress in pepper; in addition, CaPHD9, CaPHD10, CaPHD11, CaPHD17, CaPHD19, CaPHD20, and CaPHD43 were not sensitive to abiotic stress or hormonal factors. This study will provide the basis for further research into the function of CaPHD genes in plant development and responses to abiotic stresses and hormones.

Ethylene-Inducible AP2/ERF Transcription Factor Involved in the Capsaicinoid Biosynthesis in Capsicum.

Ethylene is very important in the process of plant development and regulates the biosynthesis of many secondary metabolites. In these regulatory mechanisms, transcription factors (TFs) that mediate ethylene signals play a very important role. Capsaicinoids (CAPs) are only synthesized and accumulated in Capsicum species, causing their fruit to have a special pungent taste, which can protect against attack from herbivores and pathogens. In this study, we identified the TF CcERF2, which is induced by ethylene, and demonstrated its regulatory effect on CAPs biosynthesis. Transcriptome sequencing analysis revealed that the expression patterns of CcERF2 and multiple genes associated with CAPs biosynthesis were basically the same. The spatiotemporal expression results showed CcERF2 was preferentially expressed in the placenta of the spicy fruit. Ethylene can induce the expression of CcERF2 and CAPs biosynthesis genes (CBGs). CcERF2 gene silencing and 1-methylcyclopropene (1-MCP) and pyrazinamide (PZA) treatments caused a decrease in expression of CBGs and a sharp decrease in content of CAPs. The results indicated that CcERF2 was indeed involved in the regulation of structural genes of the CAPs biosynthetic pathway.

Orf165 is associated with cytoplasmic male sterility in pepper.

Cytoplasmic male sterility (CMS) is a maternally inherited trait that derives from the inability to produce functional pollen in higher plants. CMS results from recombination of the mitochondrial genome. However, understanding of the molecular mechanism of CMS in pepper is limited. In this study, comparative transcriptomic analyses were performed using a near-isogenic CMS line 14A (CMS-14A) and a maintainer line 14B (ML-14B) as experimental materials. A total of 17,349 differentially expressed genes were detected between CMS-14A and ML-14B at the PMC meiosis stage. Among them, six unigenes associated with CMS and 108 unigenes involved in energy metabolism were identified. The gene orf165 was found in CMS-14A. When orf165 was introduced into ML-14B, almost 30% of transgenic plants were CMS. In addition, orf165 expression in transgenic CMS plants resulted in abnormal function of some genes involved in energy metabolism. When orf165 in transgenic CMS plant was silenced, the resulted orf165-silenced plant was male fertile and the expression patterns of some genes associated with energy metabolism were similar to ML-14B. Thus, we confirmed that orf165 influenced CMS in pepper.

Flower transcriptome dynamics during nectary development in pepper (Capsicum annuum L.).

The measurement of gene expression can provide important information about gene function and the molecular basis for developmental processes. We analyzed the transcriptomes at three different developmental stages of pepper flower [sporogenous cell division, stage (B1); pollen mother cell meiosis, stage (B2); and open flower (B3)]. In the cDNA libraries for B1, B2, and B3: 82718, 77061, and 91491 unigenes were assembled, respectively. A total of 34,445 unigene sequences and 128 pathways were annotated by KEGG pathway analysis. Several genes associated with nectar biosynthesis and nectary development were identified, and 8,955, 12,182, and 23,667 DEGs were identified in the B2 vs B1, B3 vs B1, and B3 vs. B2 comparisons. DEGs were involved in various metabolic processes, including flower development, nectar biosynthesis, and nectary development. According to the RNA-seq data, all 13 selected DEGs showed similar expression patterns after q-PCR analysis. Sucrose-phosphatase, galactinol-sucrose galactosyltransferase, and sucrose synthase played very important roles in nectar biosynthesis, and CRABS CLAW could potentially be involved in mediating nectary development. A significant number of simple sequence repeat and single nucleotide polymorphism markers were predicted in the Capsicum annuum sequences. The new results provide valuable genetic information about flower development in pepper.