A Phytochrome-Interacting Factor Gene CaPIF7a Positively Regulates the Defense Response against Phytophthora capsici Infection in Pepper (Capsicum annuum L.)

Phytochrome-interacting factor (PIF) is a subfamily of the basic helix–loop–helix (bHLH) transcription factors (TFs) and plays key roles in plant responses to diverse biotic and abiotic stresses. In this work, a PIF gene named CaPIF7a was cloned and its role in the regulation of pepper’s resistance to Phytophthora capsici infection (PCI) was studied. The cloned CaPIF7a gene has a CDS length of 1383 bp, encodes a hydrophilic protein containing bHLH and APB characteristic domains, and subcellular localization results showed that CaPIF7a was located in the nucleus. Expression analysis showed that CaPIF7a gene has the highest expression level in leaf, and its expression was regulated under PCI and salicylic acid (SA) treatment. Silencing of CaPIF7a in pepper plants by virus-induced gene silencing (VIGS) reduces the resistance of pepper to PCI, with decreased expression of SA-responsive and SA-biosynthesis genes and obviously decreased SA content. DNA affinity purification sequencing (DAP-seq) was employed to identify the potential targets of CaPIF7a, and yeast one-hybrid (Y1H) verified that CaPIF7a could regulate the expression of CaHY5 by binding its promoter. These findings indicated that CaPIF7a might be a key modulator in plant immune response and presented a possible regulatory network of CaPIF7a in PCI.