Department of Animal Science, Institute of Agricultural Science and Technology, College of Agriculture & Life Sciences, Chonnam National University, Gwangju 61186, Republic of Korea.
Core-Facility Center for High-Tech Materials Analysis, Gyeongsang National University, Jinju, Republic of Korea.
J Plant Physiol. 2024 Nov;302:154323. doi: 10.1016/j.jplph.2024.154323. Epub 2024 Aug 2.
Pathogen-responsive immune-related genes (resistance genes [R-genes]) and hormones are crucial mediators of systemic acquired resistance (SAR). However, their integrated functions in regulating SAR signaling components in local and distal leaves remain largely unknown. To characterize SAR in the Xanthomonas campestris pv. campestris (Xcc)-Brassica napus pathosystem, the responses of R-genes, (leaf and phloem) hormone levels, HO levels, and Ca signaling-related genes were assessed in local and distal leaves of plants exposed to four Xcc-treatments: Non-inoculation (control), only secondary Xcc-inoculation in distal leaves (C-Xcc), only primary Xcc-inoculation in local leaves (Xcc), and both primary and secondary Xcc-inoculation (X-Xcc). The primary Xcc-inoculation provoked disease symptoms as evidenced by enlarged destructive necrosis in the local leaves of Xcc and X-Xcc plants 7 days post-inoculation. Comparing visual symptoms in distal leaves 5 days post-secondary inoculation, yellowish necrotic lesions were clearly observed in non Xcc-primed plants (C-Xcc), whereas no visual symptom was developed in Xcc-primed plants (X-Xcc), demonstrating SAR. Pathogen resistance in X-Xcc plants was characterized by distinct upregulations in expression of the PAMP-triggered immunity (PTI)-related kinase-encoding gene, BIK1, the (CC-NB-LRR-type) R-gene, ZAR1, and its signaling-related gene, NDR1, with a concurrent enhancement of the kinase-encoding gene, MAPK6, and a depression of the (TIR-NB-LRR-type) R-gene, TAO1, and its signaling-related gene, SGT1, in distal leaves. Further, in X-Xcc plants, higher salicylic acid (SA) and jasmonic acid (JA) levels, both in phloem and distal leaves, were accompanied by enhanced expressions of the SA-signaling gene, NPR3, the JA-signaling genes, LOX2 and PDF1.2, and the Ca-signaling genes, CAS and CBP60g. However, in distal leaves of C-Xcc plants, an increase in SA level resulted in an antagonistic depression of JA, which enhanced only SA-dependent signaling, EDS1 and NPR1. These results demonstrate that primary Xcc-inoculation in local leaves induces resistance to subsequent pathogen attack by upregulating BIK1-ZAR1-mediated synergistic interactions with SA and JA signaling as a crucial component of SAR.
病原响应免疫相关基因（抗性基因[R 基因]）和激素是系统获得抗性（SAR）的关键介质。然而，它们在调节局部和远端叶片中 SAR 信号成分的综合功能在很大程度上仍然未知。为了表征黄单胞菌 pv. 油菜（Xcc）-油菜（Brassica napus）病理系统中的 SAR，评估了暴露于四种 Xcc 处理的植物的局部和远端叶片中的 R 基因、（叶片和韧皮部）激素水平、HO 水平和 Ca 信号相关基因的反应：非接种（对照）、仅在远端叶片中进行二次 Xcc 接种（C-Xcc）、仅在本地叶片中进行原发性 Xcc 接种（Xcc）以及原发性和继发性 Xcc 接种（X-Xcc）。初级 Xcc 接种在接种后 7 天引起局部叶片破坏性坏死扩大，证明了局部叶片中的疾病症状。比较次级接种后 5 天远端叶片的视觉症状，在未接种 Xcc 的植物（C-Xcc）中明显观察到黄色坏死病变，而在接种 Xcc 的植物（X-Xcc）中未出现视觉症状，证明了 SAR。X-Xcc 植物中的病原体抗性表现为 PAMP 触发免疫（PTI）相关激酶编码基因 BIK1、（CC-NB-LRR 型）R 基因 ZAR1 及其信号相关基因 NDR1 的表达明显上调，同时增强激酶编码基因 MAPK6 和（TIR-NB-LRR 型）R 基因 TAO1 及其信号相关基因 SGT1 的下调，在远端叶片中。此外，在 X-Xcc 植物中，韧皮部和远端叶片中水杨酸（SA）和茉莉酸（JA）水平升高，同时伴随着 SA 信号基因 NPR3、JA 信号基因 LOX2 和 PDF1.2 以及 Ca 信号基因 CAS 和 CBP60g 的表达增强。然而，在 C-Xcc 植物的远端叶片中，SA 水平的增加导致 JA 的拮抗下调，这仅增强了 SA 依赖性信号传导、EDS1 和 NPR1。这些结果表明，局部叶片中的初级 Xcc 接种诱导对随后病原体攻击的抗性，这是通过上调 BIK1-ZAR1 介导的与 SA 和 JA 信号协同作用来实现的，这是 SAR 的一个关键组成部分。
