State Key Laboratory of Crop Biology, College of Life Sciences, Shandong Agricultural University, Tai'an 271018, China.
Plant Physiol. 2021 Jul 6;186(3):1645-1659. doi: 10.1093/plphys/kiab164.
Plants use a dual defense system to cope with microbial pathogens. The first involves pathogen-associated molecular pattern-triggered immunity which is conferred by membrane receptors, and the second involves effector-triggered immunity (ETI), which is conferred by disease-resistance proteins (nucleotide-binding leucine-rich repeat-containing proteins; NLRs). Calmodulin-Binding Protein 60 (CBP60) family transcription factors are crucial for pathogen defense: CBP60g and Systemic Acquired Resistance Deficient 1 (SARD1) positively regulate immunity, whereas CBP60a negatively regulates immunity. The roles of other Arabidopsis (Arabidopsis thaliana) CBP60s remain unclear. We report that CBP60b positively regulates immunity and is redundant with-yet distinct from-CBP60g and SARD1. By combining chromatin immunoprecipitation-PCRs and luciferase reporter assays, we demonstrate that CBP60b is a transcriptional activator of immunity genes. Surprisingly, CBP60b loss-of-function results in autoimmunity, exhibiting a phenotype similar to that of CBP60b gain-of-function. Mutations at the ENHANCED DISEASE SUSCEPTIBILITY 1-PHYTOALEXIN DEFICIENT 4-dependent ETI pathway fully suppressed the defects of CBP60b loss-of-function but not those of CBP60b gain-of-function, suggesting that CBP60b is monitored by NLRs. Functional loss of SUPPRESSOR OF NPR1-1, CONSTITUTIVE 1, an R-gene, partially rescued the phenotype of cbp60b, further supporting that CBP60b is a protein targeted by pathogen effectors, that is, a guardee. Unlike CBP60g and SARD1, CBP60b is constitutively and highly expressed in unchallenged plants. Transcriptional and genetic studies further suggest that CBP60b plays a role redundant with CBP60g and SARD1 in pathogen-induced defense, whereas CBP60b has a distinct role in basal defense, partially via direct regulation of CBP60g and SARD1.
植物利用双重防御系统来应对微生物病原体。第一种涉及病原体相关分子模式触发的免疫，由膜受体赋予，第二种涉及效应物触发的免疫（ETI），由抗病蛋白（核苷酸结合富含亮氨酸重复蛋白；NLRs）赋予。钙调素结合蛋白 60（CBP60）家族转录因子对于病原体防御至关重要：CBP60g 和系统性获得抗性缺陷 1（SARD1）正向调节免疫，而 CBP60a 负向调节免疫。其他拟南芥（Arabidopsis thaliana）CBP60 的作用尚不清楚。我们报告 CBP60b 正向调节免疫，并且与 CBP60g 和 SARD1 冗余但不同。通过结合染色质免疫沉淀-PCR 和荧光素酶报告基因分析，我们证明 CBP60b 是免疫基因的转录激活因子。令人惊讶的是，CBP60b 功能丧失导致自身免疫，表现出与 CBP60b 功能获得相似的表型。增强疾病易感性 1-植物素缺乏 4 依赖的 ETI 途径突变完全抑制了 CBP60b 功能丧失的缺陷，但没有抑制 CBP60b 功能获得的缺陷，表明 CBP60b 受到 NLRs 的监测。R 基因 NPR1-1、组成型 1 的抑制物的功能丧失部分挽救了 cbp60b 的表型，进一步支持 CBP60b 是病原体效应物靶向的蛋白质，即保护者。与 CBP60g 和 SARD1 不同，CBP60b 在未受挑战的植物中持续且高度表达。转录和遗传研究进一步表明，CBP60b 在病原体诱导的防御中与 CBP60g 和 SARD1 发挥冗余作用，而 CBP60b 在基础防御中具有独特作用，部分通过直接调节 CBP60g 和 SARD1。
