Potato (Solanum tuberosum L.) is the worldwide most important nongrain crop after wheat, rice, and maize. The autotetraploidy of the modern commercial potato makes breeding of new resistant and high-yielding cultivars challenging due to complicated and time-consuming identification and selection processes of desired crop features. On the other hand, plant protection of existing cultivars using conventional synthetic pesticides is increasingly restricted due to safety issues for both consumers and the environment. Chitosan is known to display antimicrobial activity against a broad range of plant pathogens and shows the ability to trigger resistance in plants by elicitation of defense responses. As chitosan is a renewable, biodegradable and nontoxic compound, it is considered as a promising next-generation plant-protecting agent. However, the molecular and cellular modes of action of chitosan treatment are not yet understood. In this study, transcriptional changes in chitosan-treated potato leaves were investigated via RNA sequencing. Leaves treated with a well-defined chitosan polymer at low concentration were harvested 2 and 5 h after treatment and their expression profile was compared against water-treated control plants. We observed 32 differentially expressed genes (fold change ≥ 1; p-value ≤ 0.05) 2 h after treatment and 83 differentially expressed genes 5 h after treatment. Enrichment analysis mainly revealed gene modulation associated with electron transfer chains in chloroplasts and mitochondria, accompanied by the upregulation of only a very limited number of genes directly related to defense. As chitosan positively influences plant growth, yield, and resistance, we conclude that activation of electron transfer might result in the crosstalk of different organelles via redox signals to activate immune responses in preparation for pathogen attack, concomitantly resulting in a generally improved metabolic state, fostering plant growth and development. This conclusion is supported by the rapid and transient production of reactive oxygen species in a typical oxidative burst in the potato leaves upon chitosan treatment. This study furthers our knowledge on the mode of action of chitosan as a plant-protecting agent, as a prerequisite for improving its ability to replace or reduce the use of less environmentally friendly agro-chemicals.

土豆 （马铃薯L.) 是继小麦、水稻和玉米之后世界上最重要的非谷物作物。现代商业马铃薯的同源四倍体使得新的抗性和高产品种的育种具有挑战性，因为所需作物特征的鉴定和选择过程复杂且耗时。另一方面，由于消费者和环境的安全问题，使用传统合成农药对现有品种进行植物保护越来越受到限制。众所周知，壳聚糖对多种植物病原体具有抗菌活性，并且能够通过引发防御反应来触发植物的抗性。由于壳聚糖是一种可再生、可生物降解且无毒的化合物，因此被认为是有前途的下一代植物保护剂。然而，壳聚糖治疗的分子和细胞作用模式尚不清楚。在这项研究中，研究了壳聚糖处理的马铃薯叶子的转录变化通过RNA测序。在处理后2小时和5小时收获用低浓度的明确壳聚糖聚合物处理的叶子，并将它们的表达谱与水处理的对照植物进行比较。我们在治疗后2小时观察到32个差异表达基因（倍数变化≥1；p值≤0.05），在治疗后5小时观察到83个差异表达基因。富集分析主要揭示了与叶绿体和线粒体中电子传递链相关的基因调节，同时伴随着极少数与防御直接相关的基因的上调。由于壳聚糖对植物生长、产量和抗性有积极影响，我们得出结论，电子转移的激活可能会导致不同细胞器的串扰通过氧化还原信号激活免疫反应，为病原体攻击做好准备，同时导致代谢状态普遍改善，促进植物生长和发育。这一结论得到了壳聚糖处理后马铃薯叶片典型氧化爆发中活性氧快速瞬时产生的支持。这项研究进一步加深了我们对壳聚糖作为植物保护剂的作用方式的认识，这是提高其替代或减少不太环保的农用化学品的使用能力的先决条件。