Brazilian Biosciences National Laboratory (LNBio), Brazilian Center for Research in Energy and Materials (CNPEM), Campinas, Brazil.
Mol Plant Pathol. 2023 Apr;24(4):331-345. doi: 10.1111/mpp.13300. Epub 2023 Jan 24.
Citrus cancer, caused by strains of Xanthomonas citri (Xc) and Xanthomonas aurantifolii (Xa), is one of the most economically important citrus diseases. Although our understanding of the molecular mechanisms underlying citrus canker development has advanced remarkably in recent years, exactly how citrus plants fight against these pathogens remains largely unclear. Using a Xa pathotype C strain that infects Mexican lime only and sweet oranges as a pathosystem to study the immune response triggered by this bacterium in these hosts, we herein report that the Xa flagellin C protein (XaFliC) acts as a potent defence elicitor in sweet oranges. Just as Xa blocked canker formation when coinfiltrated with Xc in sweet orange leaves, two polymorphic XaFliC peptides designated flgIII-20 and flgIII-27, not related to flg22 or flgII-28 but found in many Xanthomonas species, were sufficient to protect sweet orange plants from Xc infection. Accordingly, ectopic expression of XaFliC in a Xc FliC-defective mutant completely abolished the ability of this mutant to grow and cause canker in sweet orange but not Mexican lime plants. Because XaFliC and flgIII-27 also specifically induced the expression of several defence-related genes, our data suggest that XaFliC acts as a main immune response determinant in sweet orange plants.
柑橘溃疡病由柑橘溃疡病菌（Xanthomonas citri，Xc）和柑橘黄单胞菌（Xanthomonas aurantifolii，Xa）引起，是柑橘最重要的经济病害之一。尽管近年来我们对柑橘溃疡病发病机制的分子基础有了显著的了解，但柑橘植物如何对抗这些病原体仍在很大程度上不清楚。本研究以仅感染墨西哥莱檬且感染甜橙的 Xa 血清型菌株为研究系统，研究了该细菌在这些宿主中引发的免疫反应，结果表明 Xa 鞭毛蛋白 C （XaFliC）在甜橙中作为一种有效的防御激发子。正如 Xa 与 Xc 在甜橙叶片共注射时能阻止溃疡形成一样，两种多态性的 XaFliC 肽 flgIII-20 和 flgIII-27，与 flg22 或 flgII-28 无关，但在许多黄单胞菌物种中都有发现，足以保护甜橙植物免受 Xc 感染。因此，在 Xc FliC 缺陷突变体中异位表达 XaFliC 完全消除了该突变体在甜橙而非墨西哥莱檬植株中生长和引起溃疡的能力。由于 XaFliC 和 flgIII-27 也特异性诱导了几个防御相关基因的表达，我们的数据表明 XaFliC 是甜橙植物中主要的免疫反应决定因子。
