Fukunaga Satoshi, Sogame Miho, Hata Masaki, Singkaravanit-Ogawa Suthitar, Piślewska-Bednarek Mariola, Onozawa-Komori Mariko, Nishiuchi Takumi, Hiruma Kei, Saitoh Hiromasa, Terauchi Ryohei, Kitakura Saeko, Inoue Yoshihiro, Bednarek Paweł, Schulze-Lefert Paul, Takano Yoshitaka
Graduate School of Agriculture, Kyoto University, Kyoto, Japan.
Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznan, Poland.
Plant J. 2017 Jan;89(2):381-393. doi: 10.1111/tpj.13391. Epub 2017 Jan 7.
Plant immune responses triggered upon recognition of microbe-associated molecular patterns (MAMPs) typically restrict pathogen growth without a host cell death response. We isolated two Arabidopsis mutants, derived from accession Col-0, that activated cell death upon inoculation with nonadapted fungal pathogens. Notably, the mutants triggered cell death also when treated with bacterial MAMPs such as flg22. Positional cloning identified NSL1 (Necrotic Spotted Lesion 1) as a responsible gene for the phenotype of the two mutants, whereas nsl1 mutations of the accession No-0 resulted in necrotic lesion formation without pathogen inoculation. NSL1 encodes a protein of unknown function containing a putative membrane-attack complex/perforin (MACPF) domain. The application of flg22 increased salicylic acid (SA) accumulation in the nsl1 plants derived from Col-0, while depletion of isochorismate synthase 1 repressed flg22-inducible lesion formation, indicating that elevated SA is needed for the cell death response. nsl1 plants of Col-0 responded to flg22 treatment with an RBOHD-dependent oxidative burst, but this response was dispensable for the nsl1-dependent cell death. Surprisingly, loss-of-function mutations in PEN2, involved in the metabolism of tryptophan (Trp)-derived indole glucosinolates, suppressed the flg22-induced and nsl1-dependent cell death. Moreover, the increased accumulation of SA in the nsl1 plants was abrogated by blocking Trp-derived secondary metabolite biosynthesis, whereas the nsl1-dependent hyperaccumulation of PEN2-dependent compounds was unaffected when the SA biosynthesis pathway was blocked. Collectively, these findings suggest that MAMP-triggered immunity activates a genetically programmed cell death in the absence of the functional MACPF domain protein NSL1 via Trp-derived secondary metabolite-mediated activation of the SA pathway.
植物在识别微生物相关分子模式（MAMPs）后触发的免疫反应通常会限制病原体生长，而不会引发宿主细胞死亡反应。我们从Col-0生态型中分离出两个拟南芥突变体，它们在接种非适应性真菌病原体后会激活细胞死亡。值得注意的是，这些突变体在用细菌MAMPs（如flg22）处理时也会触发细胞死亡。通过定位克隆确定NSL1（坏死斑点病变1）是这两个突变体表型的责任基因，而No-0生态型的nsl1突变在未接种病原体时会导致坏死病变形成。NSL1编码一种功能未知的蛋白质，含有一个假定的膜攻击复合物/穿孔素（MACPF）结构域。flg22的应用增加了来自Col-0的nsl1植物中水杨酸（SA）的积累，而异分支酸合成酶1的缺失抑制了flg22诱导的病变形成，表明细胞死亡反应需要升高的SA。Col-0的nsl1植物对flg22处理的反应是依赖RBOHD的氧化爆发，但这种反应对于nsl1依赖的细胞死亡是可有可无的。令人惊讶的是，参与色氨酸（Trp）衍生的吲哚硫代葡萄糖苷代谢的PEN2功能丧失突变抑制了flg22诱导的和nsl1依赖的细胞死亡。此外，通过阻断Trp衍生的次生代谢物生物合成，nsl1植物中SA的积累增加被消除，而当SA生物合成途径被阻断时，PEN2依赖化合物的nsl1依赖的超积累不受影响。总的来说，这些发现表明，在缺乏功能性MACPF结构域蛋白NSL1的情况下，MAMP触发的免疫通过Trp衍生的次生代谢物介导的SA途径激活，从而引发基因编程的细胞死亡。
