Laboratory of Genetic Breeding in Tomato, College of Horticulture and Landscape Architecture, Northeast Agricultural University, Harbin, 150030, People's Republic of China.
BMC Genomics. 2020 Mar 23;21(1):250. doi: 10.1186/s12864-020-6654-5.
The Mi-1 gene was the first identified and cloned gene that provides resistance to root-knot nematodes (RKNs) in cultivated tomato. However, owing to its temperature sensitivity, this gene does not meet the need for breeding disease-resistant plants that grow under high temperature. In this study, Mi-3 was isolated from the wild species PI 126443 (LA3858) and was shown to display heat-stable resistance to RKNs. However, the mechanism that regulates this resistance remains unknown.
In this study, 4760, 1024 and 137 differentially expressed genes (DEGs) were enriched on the basis of pairwise comparisons (34 °C vs. 25 °C) at 0 (before inoculation), 3 and 6 days post-inoculation (dpi), respectively. A total of 7035 DEGs were identified from line LA3858 in the respective groups under the different soil temperature treatments. At 3 dpi, most DEGs were enriched in Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways related to plant biotic responses, such as "plant-pathogen interaction" and "plant hormone signal transduction". Significantly enriched DEGs were found to encode key proteins such as R proteins and heat-shock proteins (HSPs). Moreover, other DEGs were found to participate in Ca signal transduction; the production of ROS; DEGs encoding transcription factors (TFs) from the bHLH, TGA, ERF, heat-shock transcription factor (HSF) and WRKY families were highly expressed, which contribute to be involved into the formation of phytohormones, such as salicylic acid (SA), jasmonic acid (JA) and ethylene (ET), the expression of most was upregulated at 3 dpi at the 25 °C soil temperature compared with the 34 °C soil temperature.
Taken together, the results of our study revealed reliable candidate genes from wild materials LA3858, that are related to Mi-3-mediate resistance to Meloidogyne incognita. A large number of vital pathways and DEGs were expressed specifically in accession LA3858 grown at 34 °C and 25 °C soil temperatures at 3 dpi. Upon infection by RKNs, pattern-recognition receptors (PRRs) specifically recognized conserved pathogen-associated molecular patterns (PAMPs) as a result of pathogen-triggered immunity (PTI), and the downstream defensive signal transduction pathway was likely activated through Ca signal channels. The expression of various TFs was induced to synthesize phytohormones and activate R proteins related to resistance, resulting in the development of effector-triggered immunity (ETI). Last, a hypersensitive response in the roots occurred, which was probably induced by the accumulation of ROS.
Mi-1 基因是第一个被鉴定和克隆的基因，它能为栽培番茄提供抗根结线虫（RKNs）的抗性。然而，由于其对温度敏感，该基因不能满足在高温下培育抗病植物的需要。本研究从野生种 PI 126443（LA3858）中分离出 Mi-3，发现其对 RKNs 具有热稳定抗性。然而，调节这种抗性的机制尚不清楚。
在本研究中，基于 34°C 与 25°C 下（接种前）、0、3 和 6 dpi 的两两比较，分别富集了 4760、1024 和 137 个差异表达基因（DEGs）。在不同土壤温度处理下，LA3858 系在各自组中鉴定出 7035 个 DEGs。在 3dpi 时，大多数 DEGs 富集在与植物生物反应相关的京都基因与基因组百科全书（KEGG）途径中，如“植物-病原体相互作用”和“植物激素信号转导”。发现显著富集的 DEGs 编码关键蛋白，如 R 蛋白和热休克蛋白（HSPs）。此外，其他 DEGs 参与 Ca 信号转导；活性氧（ROS）的产生；bHLH、TGA、ERF、热休克转录因子（HSF）和 WRKY 家族的转录因子（TFs）编码的 DEGs 高表达，有助于形成植物激素，如水杨酸（SA）、茉莉酸（JA）和乙烯（ET），与 34°C 土壤温度相比，大多数在 3dpi 时在 25°C 土壤温度下表达上调。
综上所述，本研究从野生材料 LA3858 中筛选出与 Mi-3 介导的抗南方根结线虫相关的可靠候选基因。在 3dpi 时，大量重要的途径和 DEGs 在 LA3858 中特异性表达，LA3858 在 34°C 和 25°C 的土壤温度下生长。当 RKNs 感染时，模式识别受体（PRRs）特异性地识别保守的病原体相关分子模式（PAMPs），作为病原体触发免疫（PTI）的结果，下游防御信号转导途径可能通过 Ca 信号通道激活。各种 TF 的表达被诱导合成植物激素并激活与抗性相关的 R 蛋白，从而导致效应物触发免疫（ETI）的发展。最后，可能是由于 ROS 的积累，在根部发生了过敏反应。
