National Education Minister Key Laboratory of Plant Genetic Improvement and Comprehensive Utilization, Fujian Agriculture and Forestry University, Fuzhou, Fujian, 350002, China.
Key Laboratory of Applied Genetics of Universities in Fujian Province, Fujian Agriculture and Forestry University, Fuzhou, Fujian, 350002, China.
Environ Microbiol. 2019 Dec;21(12):4537-4547. doi: 10.1111/1462-2920.14744. Epub 2019 Aug 2.
Chitin is a structural and functional component of the fungal cell wall and also serves as a pathogen-associated molecular pattern (PAMP) that triggers the innate immune responses of host plants. However, no or very little chitin is found in the fungus-like oomycetes. In Phytophthora spp., the presence of chitin has not been demonstrated so far, although putative chitin synthase (CHS) genes, which encode the enzymes that synthesize chitin, are present in their genomes. Here, we revealed that chitin is present in the zoospores and released sporangia of Phytophthora, and this is most consistent with the transcriptional pattern of PcCHS in Phytophthora capsici and PsCHS1 in Phytophthora sojae. Disruption of the CHS genes indicated that PcCHS and PsCHS1, but not PsCHS2 (which exhibited very weak transcription), have similar functions involved in mycelial growth, sporangial production, zoospore release and the pathogenesis of P. capsici and P. sojae. We also suggest that chitin in the zoospores of P. capsici can act as a PAMP that is recognized by the chitin receptors AtLYK5 or AtCERK1 of Arabidopsis. These results provide new insights into the biological significance of chitin and CHSs in Phytophthora and help with the identification of potential targets for disease control.
几丁质是真菌细胞壁的结构和功能成分，也是一种病原体相关分子模式（PAMP），可以触发宿主植物的先天免疫反应。然而，在真菌样卵菌中几乎没有或不存在几丁质。在 Phytophthora 属中，目前尚未证明存在几丁质，尽管它们的基因组中存在假定的几丁质合酶（CHS）基因，这些基因编码合成几丁质的酶。在这里，我们揭示了几丁质存在于 Phytophthora 的游动孢子和释放的游动孢子囊中，这与 Phytophthora capsici 中的 PcCHS 和 Phytophthora sojae 中的 PsCHS1 的转录模式最为一致。CHS 基因的敲除表明 PcCHS 和 PsCHS1（而不是转录活性非常弱的 PsCHS2）具有相似的功能，涉及菌丝生长、游动孢子囊产生、游动孢子释放以及 P. capsici 和 P. sojae 的致病性。我们还提出，P. capsici 游动孢子中的几丁质可以作为 PAMP，被拟南芥的 chitin 受体 AtLYK5 或 AtCERK1 识别。这些结果为 Phytophthora 中几丁质和 CHS 的生物学意义提供了新的见解，并有助于确定潜在的疾病控制靶标。
