The Plant Chemetics Laboratory, Department of Biology, University of Oxford, Oxford, UK.
School of Biological Sciences, University of Bristol, Bristol, UK.
Nat Commun. 2024 Nov 30;15(1):10431. doi: 10.1038/s41467-024-54790-1.
Most angiosperm plants recognise the 22-residue flagellin (flg22) epitope in bacterial flagellin via homologs of cell surface receptor FLS2 (flagellin sensitive-2) and mount pattern-triggered immune responses. However, flg22 is buried within the flagellin protein indicating that proteases might be required for flg22 release. Here, we demonstrate the extracellular subtilase SBT5.2 not only releases flg22, but also inactivates the immunogenicity of flagellin and flg22 by cleaving within the flg22 epitope, consistent with previous reports that flg22 is unstable in the apoplast. The prolonged lifetime of flg22 in sbt5.2 mutant plants results in increased bacterial immunity in priming assays, indicating that SBT5.2 counterbalances flagellin immunogenicity to provide spatial-temporal control and restrict costly immune responses and that bacteria take advantage of the host proteolytic machinery to avoid detection by flagellin having a protease-sensitive flg22 epitope.
大多数被子植物通过细胞表面受体 FLS2（flagellin sensitive-2）的同源物识别细菌鞭毛蛋白中的 22 残基鞭毛素（flg22）表位，并引发模式触发的免疫反应。然而，flg22 埋藏在鞭毛蛋白中，这表明可能需要蛋白酶来释放 flg22。在这里，我们证明了细胞外枯草杆菌蛋白酶 SBT5.2 不仅可以释放 flg22，还可以通过在 flg22 表位内切割来使鞭毛蛋白和 flg22 的免疫原性失活，这与先前报道的 flg22 在质外体中不稳定的情况一致。在 sbt5.2 突变体植物中，flg22 的寿命延长导致在启动测定中增强了细菌免疫力，表明 SBT5.2 抵消了鞭毛蛋白的免疫原性，以提供时空控制并限制昂贵的免疫反应，并且细菌利用宿主蛋白酶机制来避免检测到具有蛋白酶敏感的 flg22 表位的鞭毛蛋白。
