Key Laboratory of Horticultural Plant Biology, Ministry of Education, College of Horticulture and Forestry Sciences, Huazhong Agricultural University, Wuhan, China.
Department of Plant and Microbial Biology, University of California, Berkeley, Berkeley, CA, United States of America.
PLoS Pathog. 2018 Jan 2;14(1):e1006756. doi: 10.1371/journal.ppat.1006756. eCollection 2018 Jan.
Plant genomes encode large numbers of nucleotide-binding (NB) leucine-rich repeat (LRR) immune receptors (NLR) that mediate effector triggered immunity (ETI) and play key roles in protecting crops from diseases caused by devastating pathogens. Fitness costs are associated with plant NLR genes and regulation of NLR genes by micro(mi)RNAs and phased small interfering RNAs (phasiRNA) is proposed as a mechanism for reducing these fitness costs. However, whether NLR expression and NLR-mediated immunity are regulated during plant growth is unclear. We conducted genome-wide transcriptome analysis and showed that NLR expression gradually increased while expression of their regulatory small RNAs (sRNA) gradually decreased as plants matured, indicating that sRNAs could play a role in regulating NLR expression during plant growth. We further tested the role of miRNA in the growth regulation of NLRs using the tobacco mosaic virus (TMV) resistance gene N, which was targeted by miR6019 and miR6020. We showed that N-mediated resistance to TMV effectively restricted this virus to the infected leaves of 6-week old plants, whereas TMV infection was lethal in 1- and 3-week old seedlings due to virus-induced systemic necrosis. We further found that N transcript levels gradually increased while miR6019 levels gradually decreased during seedling maturation that occurs in the weeks after germination. Analyses of reporter genes in transgenic plants showed that growth regulation of N expression was post-transcriptionally mediated by MIR6019/6020 whereas MIR6019/6020 was regulated at the transcriptional level during plant growth. TMV infection of MIR6019/6020 transgenic plants indicated a key role for miR6019-triggered phasiRNA production for regulation of N-mediated immunity. Together our results demonstrate a mechanistic role for miRNAs in regulating innate immunity during plant growth.
植物基因组编码大量核苷酸结合（NB）亮氨酸丰富重复（LRR）免疫受体（NLR），这些受体介导效应子触发免疫（ETI），并在保护作物免受破坏性病原体引起的疾病方面发挥关键作用。适应性成本与植物 NLR 基因有关，并且 micro(mi)RNA 和相分离小干扰 RNA（phasiRNA）对 NLR 基因的调控被认为是降低这些适应性成本的一种机制。然而，植物生长过程中 NLR 的表达和 NLR 介导的免疫是否受到调控尚不清楚。我们进行了全基因组转录组分析，结果表明，随着植物的成熟，NLR 的表达逐渐增加，而其调节性小 RNA（sRNA）的表达逐渐降低，这表明 sRNA 可能在植物生长过程中调节 NLR 的表达。我们进一步使用烟草花叶病毒（TMV）抗性基因 N 测试了 miRNA 在 NLR 生长调控中的作用，N 基因是 miR6019 和 miR6020 的靶标。我们表明，N 介导的对 TMV 的抗性有效地将该病毒限制在 6 周龄植物的感染叶片中，而由于病毒诱导的系统性坏死，1 至 3 周龄的幼苗中 TMV 感染是致命的。我们进一步发现，在萌发后数周的幼苗成熟过程中，N 转录本水平逐渐增加，而 miR6019 水平逐渐降低。在转基因植物中的报告基因分析表明，N 表达的生长调控是由 MIR6019/6020 进行转录后介导的，而 MIR6019/6020 在植物生长过程中受到转录水平的调节。TMV 感染 MIR6019/6020 转基因植物表明，miR6019 触发的 phasiRNA 产生对于调节 N 介导的免疫具有关键作用。总之，我们的研究结果证明了 miRNA 在植物生长过程中调节先天免疫的机制作用。
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