Laboratory of Molecular Plant Biology and KU Leuven Plant Institute, KU Leuven, Kasteelpark Arenberg 31, 3001 Leuven, Belgium.
IBSB-Industrial Biotechnology and Systems Biology Research Group, Department of Bioengineering, Marmara University, Istanbul, Turkey.
J Exp Bot. 2022 Jun 24;73(12):4214-4235. doi: 10.1093/jxb/erac140.
Carbohydrates such as fructans can be involved in priming or defence stimulation, and hence potentially provide new strategies for crop protection against biotic stress. Chicory (Cichorium intybus) is a model plant for fructan research and is a crop with many known health benefits. Using the chicory-Botrytis cinerea pathosystem, we tested the effectiveness of fructan-induced immunity, focussing on different plant and microbial fructans. Sugar dynamics were followed after priming and subsequent pathogen infection. Our results indicated that many higher plants might detect extracellular levan oligosaccharides (LOS) of microbial origin, while chicory also detects extracellular small inulin-type fructooligosaccharides (FOS) of endogenous origin, thus differing from the findings of previous fructan priming studies. No clear positive effects were observed for inulin or mixed-type fructans. An elicitor-specific burst of reactive oxygen species was observed for sulfated LOS, while FOS and LOS both behaved as genuine priming agents. In addition, a direct antifungal effect was observed for sulfated LOS. Intriguingly, LOS priming led to a temporary increase in apoplastic sugar concentrations, mainly glucose, which could trigger downstream responses. Total sugar and starch contents in total extracts of LOS-primed leaves were higher after leaf detachment, indicating they could maintain their metabolic activity. Our results indicate the importance of balancing intra- and extracellular sugar levels (osmotic balance) in the context of 'sweet immunity' pathways.
碳水化合物（如菊糖）可参与激发或防御刺激，因此为作物的生物胁迫防护提供了新的策略。菊苣（Cichorium intybus）是菊糖研究的模式植物，也是一种具有许多已知健康益处的作物。利用菊苣-葡萄孢菌病理系统，我们测试了菊糖诱导免疫的有效性，重点关注不同植物和微生物的菊糖。在激发和随后的病原体感染后，我们跟踪了糖的动态。我们的结果表明，许多高等植物可能会检测到微生物来源的胞外蔗寡糖（LOS），而菊苣还会检测到内源性的胞外小菊糖型果寡糖（FOS），这与之前的菊糖激发研究结果不同。没有观察到明显的菊糖或混合型菊糖的正向作用。对于硫酸化 LOS，观察到了一种诱导剂特异性的活性氧爆发，而 FOS 和 LOS 都表现为真正的激发剂。此外，硫酸化 LOS 还具有直接的抗真菌作用。有趣的是，LOS 激发会导致质外体糖浓度（主要是葡萄糖）的暂时增加，这可能会引发下游反应。LOS 激发叶片的总糖和淀粉含量在叶片分离后更高，表明它们可以维持其代谢活性。我们的结果表明，在“甜味免疫”途径中，平衡细胞内和细胞外糖水平（渗透平衡）的重要性。
