Ministry of Education Key Laboratory for Bio-Resource and Eco-Environment, College of Life Science, Sichuan University, Chengdu, 610064, China.
Planta. 2018 Feb;247(2):355-368. doi: 10.1007/s00425-017-2785-6. Epub 2017 Oct 9.
Tobacco EXPA4 plays a role in Nicotiana benthamiana defence against virus attack and affects antioxidative metabolism and phytohormone-mediated immunity responses in tobacco. Expansins are cell wall-loosening proteins known for their endogenous functions in cell wall extensibility during plant growth. The effects of expansins on plant growth, developmental processes and environment stress responses have been well studied. However, the exploration of expansins in plant virus resistance is rarely reported. In the present study, virus-induced gene silencing (VIGS) and Agrobacterium-mediated transient overexpression were conducted to investigate the role of Nicotiana tabacum alpha-expansin 4 (EXPA4) in modulating Tobacco mosaic virus (TMV-GFP) resistance in Nicotiana benthamiana. The results indicated that silencing of EXPA4 reduced the sensitivity of N. benthamiana to TMV-GFP, and EXPA4 overexpression accelerated virus reproduction on tobacco. In addition, our data suggested that the changes of virus accumulation in response to EXPA4 expression levels could further affect the antioxidative metabolism and phytohormone-related pathways in tobacco induced by virus inoculation. EXPA4-silenced plants with TMV-GFP have enhanced antioxidant enzymes activities, which were down-regulated in virus-inoculated 35S:EXPA4 plants. Salicylic acid accumulation and SA-mediated defence genes induced by TMV-GFP were up-regulated in EXPA4-silenced plants, but depressed in 35S:EXPA4 plants. Furthermore, a VIGS approach was used in combination with exogenous phytohormone treatments, suggesting that EXPA4 has different responses to different phytohormones. Taken together, these results suggested that EXPA4 plays a role in tobacco defence against viral pathogens.
烟草 EXPA4 在拟南芥防御病毒攻击中发挥作用，并影响烟草的抗氧化代谢和植物激素介导的免疫反应。扩展蛋白是细胞壁松弛蛋白，已知其在植物生长过程中细胞壁伸展性的内源性功能。扩展蛋白对植物生长、发育过程和环境胁迫反应的影响已经得到了很好的研究。然而，扩展蛋白在植物抗病毒方面的探索很少有报道。本研究采用病毒诱导的基因沉默（VIGS）和农杆菌介导的瞬时过表达技术，研究了烟草 alpha-扩展蛋白 4（EXPA4）在调节烟草花叶病毒（TMV-GFP）在拟南芥中的抗性中的作用。结果表明，EXPA4 的沉默降低了拟南芥对 TMV-GFP 的敏感性，而 EXPA4 的过表达加速了病毒在烟草上的繁殖。此外，我们的数据表明，病毒积累的变化对 EXPA4 表达水平的响应可以进一步影响病毒接种诱导的烟草抗氧化代谢和植物激素相关途径。感染 TMV-GFP 的 EXPA4 沉默植株的抗氧化酶活性增强，而感染病毒的 35S:EXPA4 植株中的抗氧化酶活性则下调。EXPA4 沉默植株中，水杨酸积累和 TMV-GFP 诱导的水杨酸介导的防御基因上调，但在 35S:EXPA4 植株中下调。此外，还采用 VIGS 方法结合外源植物激素处理，表明 EXPA4 对不同植物激素有不同的反应。综上所述，这些结果表明 EXPA4 在烟草抗病毒防御中发挥作用。
