A rice root-knot nematode Meloidogyne graminicola-resistant mutant rice line shows early expression of plant-defence genes.

Resistance to rice root-knot nematode Meloidogyne graminicola in a mutant rice line is suggested to be conferred by higher expression of several genes putatively involved in damage-associated molecular pattern recognition, secondary metabolite biosynthesis including phytoalexins, and defence-related genes. Meloidogyne graminicola has emerged as the most destructive plant-parasitic nematode disease of rice (Oryza sativa L.). Genetic resistance to M. graminicola is one of the most effective methods for its management. A M. graminicola-resistant O. sativa ssp. indica mutant line-9 was previously identified through a forward genetic screen (Hatzade et al. Biologia 74:1197-1217, 2019). In the present study, we used RNA-Sequencing to investigate the molecular mechanisms conferring nematode resistance to the mutant line-9 compared to the susceptible parent JBT 36/14 at 24 h post-infection. A total of 674 transcripts were differentially expressed in line-9. Early regulation of genes putatively related to nematode damage-associated molecular pattern recognition (e.g., wall-associated receptor kinases), signalling [Nucleotide-binding, Leucine-Rich Repeat (NLRs)], pathogenesis-related (PR) genes (PR1, PR10a), defence-related genes (NB-ARC domain-containing genes), as well as a large number of genes involved in secondary metabolites including diterpenoid biosynthesis (CPS2, OsKSL4, OsKSL10, Oscyp71Z2, oryzalexin synthase, and momilactone A synthase) was observed in M. graminicola-resistant mutant line-9. It may be suggested that after the nematode juveniles penetrate the roots of line-9, early recognition of invading nematodes triggers plant immune responses mediated by phytoalexins, and other defence proteins such as PR proteins inhibit nematode growth and reproduction. Our study provides the first transcriptomic comparison of nematode-resistant and susceptible rice plants in the same genetic background and adds to the understanding of mechanisms underlying plant-nematode resistance in rice.