CaHDZ27, a Homeodomain-Leucine Zipper I Protein, Positively Regulates the Resistance to Ralstonia solanacearum Infection in Pepper

• Published in: Molecular plant-microbe interactions Vol. 30; no. 12; pp. 960 - 973
• Main Authors: Mou, Shaoliang, Liu, Zhiqin, Gao, Feng, Yang, Sheng, Su, Meixia, Shen, Lei, Wu, Yang, He, Shuilin
• Format: Journal Article
• Language: English
• Published: United States The American Phytopathological Society 01-12-2017
• Subjects: Acetates - pharmacology; Amino Acid Sequence; Capsicum - drug effects; Capsicum - genetics; Capsicum - immunology; Capsicum - microbiology; Cell Death - drug effects; Cell Nucleus - drug effects; Cell Nucleus - metabolism; Cyclopentanes - pharmacology; Disease Resistance - drug effects; DNA, Plant - metabolism; Gene Expression Regulation, Plant - drug effects; Gene Silencing - drug effects; Homeodomain Proteins - metabolism; Leucine Zippers; Luminescence; Nicotiana - genetics; Organophosphorus Compounds - pharmacology; Oxylipins - pharmacology; Plant Diseases - genetics; Plant Diseases - immunology; Plant Diseases - microbiology; Plant Immunity - drug effects; Plant Leaves - drug effects; Plant Leaves - genetics; Plant Proteins - chemistry; Plant Proteins - metabolism; Plants, Genetically Modified; Protein Binding - drug effects; Protein Multimerization; Protein Transport - drug effects; Ralstonia solanacearum - drug effects; Ralstonia solanacearum - physiology; Salicylic Acid - pharmacology; Transcriptional Activation - genetics; Up-Regulation - drug effects; Up-Regulation - genetics
• ISSN: 0894-0282; 1943-7706
• DOI: 10.1094/MPMI-06-17-0130-R

Homeodomain-leucine zipper class I (HD-Zip I) transcription factors have been functionally characterized in plant responses to abiotic stresses, but their roles in plant immunity are poorly understood. Here, a HD-Zip I gene, CaHZ27, was isolated from pepper (Capsicum annum) and characterized for its role in pepper immunity. Quantitative real-time polymerase chain reaction showed that CaHDZ27 was transcriptionally induced by Ralstonia solanacearum inoculation and exogenous application of methyl jasmonate, salicylic acid, or ethephon. The CaHDZ27-green fluorescent protein fused protein was targeted exclusively to the nucleus. Chromatin immunoprecipitation demonstrated that CaHDZ27 bound to the 9-bp pseudopalindromic element (CAATAATTG) and triggered β-glucuronidase expression in a CAATAATTG-dependent manner. Virus-induced gene silencing of CaHDZ27 significantly attenuated the resistance of pepper plants against R. solanacearum and downregulated defense-related marker genes, including CaHIR1, CaACO1, CaPR1, CaPR4, CaPO2, and CaBPR1. By contrast, transient overexpression of CaHDZ27 triggered strong cell death mediated by the hypersensitive response and upregulated the tested immunity-associated marker genes. Ectopic CaHDZ27 expression in tobacco enhances its resistance against R. solanacearum. These results collectively suggest that CaHDZ27 functions as a positive regulator in pepper resistance against R. solanacearum. Bimolecular fluorescence complementation and coimmunoprecipitation assays indicate that CaHDZ27 monomers bind with each other, and this binding is enhanced significantly by R. solanacearum inoculation. We speculate that homodimerization of CaHZ27 might play a role in pepper response to R. solanacearum, further direct evidence is required to confirm it.