PSH unit, INRAE, Avignon, France.
UMR Qualisud, Avignon Université, Avignon, France.
Ann Bot. 2021 Jan 1;127(1):143-154. doi: 10.1093/aob/mcaa155.
The main soluble sugars are important components of plant defence against pathogens, but the underlying mechanisms are unclear. Upon infection by Botrytis cinerea, the activation of several sugar transporters, from both plant and fungus, illustrates the struggle for carbon resources. In sink tissues, the metabolic use of the sugars mobilized in the synthesis of defence compounds or antifungal barriers is not fully understood.
In this study, the nitrogen-dependent variation of tomato stem susceptibility to B. cinerea was used to examine, before and throughout the course of infection, the transcriptional activity of enzymes involved in sugar metabolism. Under different nitrate nutrition regimes, the expression of genes that encode the enzymes of sugar metabolism (invertases, sucrose synthases, hexokinases, fructokinases and phosphofructokinases) was determined and sugar contents were measured before inoculation and in asymptomatic tissues surrounding the lesions after inoculation.
At high nitrogen availability, decreased susceptibility was associated with the overexpression of several genes 2 d after inoculation: sucrose synthases Sl-SUS1 and Sl-SUS3, cell wall invertases Sl-LIN5 to Sl-LIN9 and some fructokinase and phosphofructokinase genes. By contrast, increased susceptibility corresponded to the early repression of several genes that encode cell wall invertase and sucrose synthase. The course of sugar contents was coherent with gene expression.
The activation of specific genes that encode sucrose synthase is required for enhanced defence. Since the overexpression of fructokinase is also associated with reduced susceptibility, it can be hypothesized that supplementary sucrose cleavage by sucrose synthases is dedicated to the production of cell wall components from UDP-glucose, or to the additional implication of fructose in the synthesis of antimicrobial compounds, or both.
主要可溶性糖是植物抵御病原体的重要组成部分，但潜在机制尚不清楚。在感染灰葡萄孢后，植物和真菌中几种糖转运蛋白的激活说明了对碳资源的争夺。在汇组织中，对于在防御化合物或抗真菌屏障合成中动员的糖的代谢利用尚不完全清楚。
在这项研究中，使用番茄茎对灰葡萄孢易感性的氮依赖性变化，在感染前后检查参与糖代谢的酶的转录活性。在不同的硝酸盐营养条件下，测定了编码糖代谢酶（转化酶、蔗糖合酶、己糖激酶、果糖激酶和磷酸果糖激酶）的基因的表达，并在接种前和接种后无症状组织中测量了糖含量。
在高氮供应下，易感性降低与接种后 2 天几种基因的过表达有关：蔗糖合酶 Sl-SUS1 和 Sl-SUS3、细胞壁转化酶 Sl-LIN5 至 Sl-LIN9 和一些果糖激酶和磷酸果糖激酶基因。相比之下，对编码细胞壁转化酶和蔗糖合酶的几个基因的早期抑制与易感性增加相对应。糖含量的变化与基因表达一致。
需要激活特定的蔗糖合酶基因以增强防御。由于果糖激酶的过表达也与易感性降低有关，因此可以假设蔗糖合酶对蔗糖的额外切割是专门用于从 UDP-葡萄糖产生细胞壁成分的，或者果糖在抗菌化合物的合成中的额外作用，或者两者兼而有之。
