Instituto de Biología Molecular y Celular de Rosario, Consejo Nacional de Investigaciones Científicas y Técnicas (IBR-CONICET) and Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario (UNR), Ocampo y Esmeralda, 2000, Rosario, Argentina.
Mol Plant Pathol. 2018 Apr;19(4):801-811. doi: 10.1111/mpp.12560. Epub 2017 May 19.
Plant natriuretic peptides (PNPs) have been implicated in the regulation of ions and water homeostasis, and their participation in the plant immune response has also been proposed. Xanthomonas citri ssp. citri contains a gene encoding a PNP-like protein (XacPNP) which has no homologues in other bacteria. XacPNP mimics its Arabidopsis thaliana homologue AtPNP-A by modifying host responses to create favourable conditions for pathogen survival. However, the ability of XacPNP to induce plant defence responses has not been investigated. In order to study further the role of XacPNP in vivo, A. thaliana lines over-expressing XacPNP, lines over-expressing AtPNP-A and AtPNP-A-deficient plants were generated. Plants over-expressing XacPNP or AtPNP-A showed larger stomatal aperture and were more resistant to saline or oxidative stress than were PNP-deficient lines. In order to study further the role of PNP in biotic stress responses, A. thaliana leaves were infiltrated with pure recombinant XacPNP, and showed enhanced expression of genes related to the defence response and a higher resistance to pathogen infections. Moreover, AtPNP-A expression increased in A. thaliana on Pseudomonas syringae pv. tomato (Pst) infection. This evidence led us to analyse the responses of the transgenic plants to pathogens. Plants over-expressing XacPNP or AtPNP-A were more resistant to Pst infection than control plants, whereas PNP-deficient plants were more susceptible and showed a stronger hypersensitive response when challenged with non-host bacteria. Therefore, XacPNP, acquired by horizontal gene transfer, is able to mimic PNP functions, even with an increase in plant defence responses.
植物利钠肽（PNP）被认为参与了离子和水稳态的调节，其在植物免疫反应中的参与也已被提出。柑橘黄单胞菌含有一个编码 PNP 样蛋白（XacPNP）的基因，该基因在其他细菌中没有同源物。XacPNP 通过修饰宿主对病原体生存的反应来模拟其拟南芥同源物 AtPNP-A，从而创造有利于病原体生存的条件。然而，XacPNP 诱导植物防御反应的能力尚未得到研究。为了进一步研究 XacPNP 在体内的作用，生成了过表达 XacPNP 的拟南芥系、过表达 AtPNP-A 的系和 AtPNP-A 缺陷型植物。过表达 XacPNP 或 AtPNP-A 的植物的气孔孔径较大，对盐胁迫或氧化胁迫的抗性比 PNP 缺陷型系更强。为了进一步研究 PNP 在生物胁迫反应中的作用，用纯重组 XacPNP 浸润拟南芥叶片，显示与防御反应相关的基因表达增强，对病原体感染的抗性更高。此外，在拟南芥感染丁香假单胞菌 pv.番茄（Pst）时，AtPNP-A 的表达增加。这一证据促使我们分析转基因植物对病原体的反应。过表达 XacPNP 或 AtPNP-A 的植物对 Pst 感染的抗性比对照植物更强，而 PNP 缺陷型植物更易感，当受到非宿主细菌的挑战时，表现出更强的过敏反应。因此，通过水平基因转移获得的 XacPNP 能够模拟 PNP 的功能，甚至增加植物的防御反应。
