Zhang Qiang, Gao Derong, Tian Lei, Feussner Kirstin, Li Bin, Yang Long, Yang Qin, Zhang Yuelin, Li Xin, Feussner Ivo, Xu Fang
The Key Laboratory of Plant Development and Environmental Adaptation Biology, Ministry of Education, Shandong Key Laboratory of Precision Molecular Crop Design and Breeding, School of Life Sciences, Shandong University, Qingdao 266237, China.
Department of Plant Biochemistry, Albrecht-von-Haller-Institute for Plant Sciences and Goettingen Center for Molecular Biosciences (GZMB), University of Goettingen, Göttingen 37077, Germany.
Plant Physiol. 2025 Feb 7;197(2). doi: 10.1093/plphys/kiaf030.
Proteins with Toll/interleukin-1 receptor (TIR) domains are widely distributed in both prokaryotes and eukaryotes, serving as essential components of immune signaling. Although monocots lack the major TIR nucleotide-binding leucine-rich repeat-type (TNL) immune receptors, they possess a small number of TIR-only proteins, the function of which remains largely unknown. In the monocot maize (Zea mays), there are 3 conserved TIR-only genes in the reference genome, namely ZmTIR1 to ZmTIR3. A genome-wide scan for TIR genes and comparative analysis revealed that these genes exhibit low sequence diversity and do not show copy number variation among 26 diverse inbred lines. ZmTIR1 and ZmTIR3, but not ZmTIR2, specifically trigger cell death and defense gene expression when overexpressed in Nicotiana benthamiana leaves. These responses depend on the critical glutamic acid and cysteine residues predicted to be essential for TIR-mediated NADase and 2',3'-cAMP/cGMP synthetase activity, respectively, as well as the key TIR downstream regulator Enhanced Disease Susceptibility 1 (EDS1). Overexpression of ZmTIR3 in N. benthamiana produces signaling molecules, including 2'cADPR, 2',3'-cAMP, and 2',3'-cGMP, a process that requires the enzymatic glutamic acid and cysteine residues of ZmTIR3. ZmTIR expression in maize is barely detectable under normal conditions but is substantially induced by different pathogens. Importantly, the maize Zmtir3 knockout mutant exhibits enhanced susceptibility to the fungal pathogen Cochliobolus heterostrophus, highlighting the role of ZmTIR3 in maize immunity. Overall, our results unveil the function of the maize ZmTIRs. We propose that the pathogen-inducible ZmTIRs play an important role in maize immunity, likely through their enzymatic activity and via EDS1-mediated signaling.
具有Toll/白细胞介素-1受体（TIR）结构域的蛋白质广泛分布于原核生物和真核生物中，是免疫信号传导的重要组成部分。虽然单子叶植物缺乏主要的TIR核苷酸结合富含亮氨酸重复型（TNL）免疫受体，但它们拥有少量仅含TIR的蛋白质，其功能在很大程度上仍不清楚。在单子叶植物玉米（Zea mays）中，参考基因组中有3个保守的仅含TIR的基因，即ZmTIR1至ZmTIR3。全基因组范围内对TIR基因的扫描和比较分析表明，这些基因表现出低序列多样性，并且在26个不同的自交系中未显示拷贝数变异。当在本氏烟草叶片中过表达时，ZmTIR1和ZmTIR3而非ZmTIR2会特异性地引发细胞死亡和防御基因表达。这些反应分别取决于预测对TIR介导的NAD酶和2',3'-cAMP/cGMP合成酶活性至关重要的关键谷氨酸和半胱氨酸残基，以及关键的TIR下游调节因子增强疾病易感性1（EDS1）。ZmTIR3在本氏烟草中的过表达会产生信号分子，包括2'cADPR、2',3'-cAMP和2',3'-cGMP，这一过程需要ZmTIR3的酶促谷氨酸和半胱氨酸残基。在正常条件下，玉米中ZmTIR的表达几乎检测不到，但会受到不同病原体的显著诱导。重要的是，玉米Zmtir3基因敲除突变体对真菌病原体玉米小斑病菌（Cochliobolus heterostrophus）的易感性增强，突出了ZmTIR3在玉米免疫中的作用。总体而言，我们的结果揭示了玉米ZmTIRs的功能。我们认为，病原体诱导的ZmTIRs可能通过其酶活性和EDS1介导的信号传导在玉米免疫中发挥重要作用。
