The Mi- 1 gene is a key regulator of defence mechanisms and cellular gene dynamics in response to root-knot nematodes.

Root-knot nematodes threaten tomato cultivation worldwide. This study confirms Mi- 1 gene's role in defence by inducing programmed cell death, lignin accumulation, and cellular remodelling in resistant plants. Root-knot nematodes, particularly Meloidogyne species, pose a significant economic threat to tomato cultivation globally. Despite the identification of various Mi genes, their mechanisms of action are not fully understood. This study aimed to elucidate the role of the Mi- 1 gene by analysing transcriptomic data from both resistant and susceptible tomato genotypes and by constitutively expressing Mi- 1 in a susceptible cultivar. Transcriptome analysis of leaf and root samples upon RKN infection showed that the Mi- 1 gene was exclusively present in the roots of resistant plants. Further to investigate its function Mi- 1 was constitutively expressed under the CaMV 35S promoter in a susceptible tomato cultivar. Structural analysis confirmed that the Mi- 1 protein primarily localized in the cytoplasm and lacked a transmembrane motif. Following transformation, a comparative gene expression of wild-type and transformed tomato plants with genes obtained from transcriptome, revealing significant up-regulation of cellular, plant defence, and programmed cell death (PCD) related genes in the transgenic lines. Notably, the roots of the transformed plants exhibited thickened root morphology and high lignin accumulation, correlating with the expression of lignin biosynthesis genes. These findings suggested that the Mi- 1 gene is not only involved in PCD but also activates various defence-related and cellular remodelling genes by depositing the lignin in the root cell to combat against nematode attack.