<i>CaCML13</i> Acts Positively in Pepper Immunity Against <i>Ralstonia solanacearum</i> Infection Forming Feedback Loop with CabZIP63

• Main Authors: Lei Shen, Sheng Yang, Deyi Guan, Shuilin He
• Format: Article
• Language: English
• Published: MDPI AG 2020-06-01
• Series: International Journal of Molecular Sciences
• Subjects: <i>Capsicum</i> <i>annuum</i>; CaCML13; CabZIP63; immunity; <i>Ralstonia solanacearum</i>
• Online Access: https://www.mdpi.com/1422-0067/21/11/4186

Ca²⁺-signaling—which requires the presence of calcium sensors such as calmodulin (CaM) and calmodulin-like (CML) proteins—is crucial for the regulation of plant immunity against pathogen attack. However, the underlying mechanisms remain elusive, especially the roles of CMLs involved in plant immunity remains largely uninvestigated. In the present study, <i>CaCML13</i>, a calmodulin-like protein of pepper that was originally found to be upregulated by <i>Ralstonia solanacearum </i>inoculation (RSI) in RNA-seq, was functionally characterized in immunity against RSI. CaCML13 was found to target the whole epidermal cell including plasma membrane, cytoplasm and nucleus. We also confirmed that<i> CaCML13</i> was upregulated by RSI in pepper roots by quantitative real-time PCR (qRT-PCR). The silencing of <i>CaCML13</i> significantly enhanced pepper plants’ susceptibility to RSI accompanied with downregulation of immunity-related <i>CaPR1</i>, <i>CaNPR1</i>, <i>CaDEF1</i> and <i>CabZIP63</i>. In contrast, <i>CaCML13</i> transient overexpression induced clear hypersensitivity-reaction (HR)-mimicked cell death and upregulation of the tested immunity-related genes. In addition, we also revealed that the G-box-containing <i>CaCML13</i> promoter was bound by CabZIP63 and <i>CaCML13</i> was positively regulated by CabZIP63 at transcriptional level. Our data collectively indicate that CaCML13 act as a positive regulator in pepper immunity against RSI forming a positive feedback loop with <i>CabZIP63</i>.