Impaired Expression of Chloroplast HSP90C Chaperone Activates Plant Defense Responses with a Possible Link to a Disease-Symptom-Like Phenotype

• Main Authors: Shaikhul Islam, Sachin Ashok Bhor, Keisuke Tanaka, Hikaru Sakamoto, Takashi Yaeno, Hidetaka Kaya, Kappei Kobayashi
• Format: Article
• Language: English
• Published: MDPI AG 2020-06-01
• Series: International Journal of Molecular Sciences
• Subjects: cell death; chlorosis; HSP90C; immune response; RNA-seq; tobacco
• Online Access: https://www.mdpi.com/1422-0067/21/12/4202
• ISSN: 1661-6596; 1422-0067

RNA-seq analysis of a transgenic tobacco plant, i-hpHSP90C, in which chloroplast HSP90C genes can be silenced in an artificially inducible manner resulting in the development of chlorosis, revealed the up- and downregulation of 2746 and 3490 genes, respectively. Gene ontology analysis of these differentially expressed genes indicated the upregulation of ROS-responsive genes; the activation of the innate immunity and cell death pathways; and the downregulation of genes involved in photosynthesis, plastid organization, and cell cycle. Cell death was confirmed by trypan blue staining and electrolyte leakage assay, and the H₂O₂ production was confirmed by diaminobenzidine staining. The results collectively suggest that the reduced levels of HSP90C chaperone lead the plant to develop chlorosis primarily through the global downregulation of chloroplast- and photosynthesis-related genes and additionally through the light-dependent production of ROS, followed by the activation of immune responses, including cell death.