番茄识别菌根因子的分子机制

The symbiosis between arbuscular mycorrhizal (AM) fungi and the majority of land plants improves the water and nutrient uptake for plants, which could offer an attractive way to reduce the use of fossil-fuel derived chemical fertilizer, improve soil health and mitigate negative environmental effects. The AM symbiosis is initiated by the signal communication between partners. Signals produced by host plants, for example strigolactones, could stimulate AM fungal germination and presymbiotic growth. After recognizing plant signals, AM fungi will secret signal molecules too, such as Myc factors, which consist of short-chain chitin backbone with various substitutions. The key step in establishing the AM symbiosis is the plant recognition of fungal signal molecules. However, how plants recognize Myc factors is still unclear. In our preliminary data, we identified the candidate receptors of Myc factors in Solanum lycopersicum, namely SlLYK10 and SlLYK11, using a reverse genetic approach. In this application, we proposed to confirm that SlLYK10 and SlLYK11 proteins could bind to Myc factors directly, and investigate the molecular mechanism how receptors bind to Myc factors and how the signal is transduced from the plasma membrane to the cytosol.

大多数陆生植物都能与丛枝菌根(AM)真菌形成互利互惠的共生关系，它可以帮助植物提高水分和矿质元素的吸收，植物与AM真菌共生分子机制的研究具有广泛生理生态学意义。而共生关系的建立是由植物识别AM真菌信号分子起始，然后根表皮细胞发生变化从而指引菌丝进一步侵入到内皮层形成丛枝结构。菌根因子是AM真菌分泌的主要信号分子之一，然而植物识别菌根因子的分子机制还不是很清楚。我们前期已经通过反向遗传学的方法筛选得到番茄识别菌根因子的候选受体SlLYK10和SlLYK11, 属于LysM受体激酶家族蛋白。本项目中我们拟进一步确认SlLYK10和SlLYK11为菌根因子受体，并对SlLYK10-SlLYK11受体复合体识别菌根因子以及信号转导的生化机制做更详细分析，初步阐明番茄识别菌根因子的分子机制，这将为AM真菌在生产上的应用提供更多科学依据和理论支撑。

丛枝菌根(AM)真菌与植物的共生由植物识别AM真菌信号分子菌根因子起始，短链几丁质(4-5个乙酰葡糖胺寡糖)或脂质几丁质寡糖是菌根因子的主要成分，植物识别菌根因子后诱导共生信号通路。而长链几丁质是真菌细胞壁的主要成分，在病原真菌侵染植物时，植物几丁质酶可以降解几丁质，产生不同长度的寡糖，6-8个乙酰葡糖胺寡糖被植物LYK受体识别，诱导免疫反应，从而限制真菌的进一步侵染。已有研究表明几丁质类化合物都是由LYK（LysM receptor kinase）家族蛋白识别，我们通过序列同源比对，鉴定了番茄LYK家族蛋白，并初步明确了SlLYK12是识别菌根因子的受体，基因沉默SlLYK12后，番茄与AM菌的共生显著减弱。SlLYK4是长链几丁质的受体，Sllyk4突变体对长链几丁质的敏感性降低。同时，我们也鉴定了几丁质受体下游的主要胞内受体激酶RIPK，番茄Slripk突变体中长链几丁质诱导的活性氧迸发水平显著下降。另外，通过进化树分析，我们认为介导免疫和共生的LYK祖先受体在番茄中发生功能分化，分别介导了免疫和共生。