Abstract
BackgroundThe 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.ResultsIn 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 Ca2+ 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.ConclusionTaken 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 Ca2+ 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.
Highlights
The Mi-1 gene was the first identified and cloned gene that provides resistance to root-knot nematodes (RKNs) in cultivated tomato
Upon infection by RKNs, pattern-recognition receptors (PRRs) 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 Ca2+ signal channels
When the plants were subjected to a soil temperature of 34 °C, gall formation on Illumina sequencing and alignment to the reference genome RNA sequencing (RNA-seq) data were generated from 18 samples of the wild species LA3858 at different stages following inoculation (0, 3 and 6 dpi)
Summary
The Mi-1 gene was the first identified and cloned gene that provides resistance to root-knot nematodes (RKNs) in cultivated tomato. Members of the genus Meloidogyne, which represent major pests worldwide, have a substantial negative influence on the development of various plant species [1]. ROS have a substantial influence on reactions to biotic and abiotic stresses. Phytohormones such as JA and SA function to regulate plant growth and are involved in plant defense signaling pathways [4]. Gpa is an R gene that encodes the GPA2 protein, which depends on the recognition specificity afforded by both amino acid 187 and the Gpa LRR domain and provides resistance against two Globodera pallida nematode populations (D383 and D372) [6]. The Rhg gene from soybean, the Me3 and Me4 genes from pepper, and the Mi-1 gene from tomato provide resistance against specific strains of nematodes
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