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.