Plant Hormone Signalling Pathways and Resistance to Plant Parasitic Nematodes

Some of the most harmful plant-parasitic nematodes are those endoparasites that invade the roots of their host and induce the formation of distinctive and metabolically active “feeding sites”. Many changes in root gene expression are required for establishment of a feeding site. Different reporters have been used to monitor these molecular changes during nematode infection, but they are either destructive or require specialized microscopy and are therefore not suitable for real-time monitoring of gene expression on a whole root system scale. Hence, we wanted to evaluate a non-destructive method for assessing nematode infection that would be easily visible in soil grown plants. The RUBY betalain reporter (He et al., 2020) was evaluated in both Arabidopsis and potato plants infected with root-knot and cyst nematodes. Arabidopsis lines carrying the CaMV35S-RUBY construct exhibited gene silencing when constitutive overexpression was detrimental, whereas in potato, the same construct drove stable RUBY expression throughout the plant’s lifespan. Notably, RUBY expression in giant cells and syncytia was maintained during nematode development in both Arabidopsis and potato. This contrasts with previous studies using GUS and GFP reporters that showed apparent silencing of the CaMV35S promoter expression in syncytia. To minimize side effects of constitutive expression, we also employed RUBY under root expressed, nematode-inducible promoters. By integrating two candidate promoter sequences upstream of the RUBY gene, two constructs (pBI:PG1-RUBY and pBI:PG2-RUBY) were generated, enabling visualization of transcriptional activation in roots of transgenic potato plants. These newly developed RUBY constructs demonstrated clear root-specificity in transgenic lines, confirming their utility as targeted visual markers. Together, these findings establish RUBY as a reliable visual marker for studying plant-nematode interactions. Another aim of our study was to identify one or more sources of resistance to potato cyst nematodes in a panel of Solanum americanum accessions. To that end, segregating F₂ generations arising from crosses between susceptible and resistant parents were tested, allowing identification of resistant individuals and analysis of inheritance patterns. To optimise screening of F₂ populations and identify effective infection conditions, the susceptible parent was tested across soil types and inoculum levels, revealing that compost and sand-loam with high nematode inoculum and root exudates significantly enhanced G. pallida populations for robust resistance screening. Segregation patterns indicated one accession with a single dominant resistance locus and a second accession with two or more unlinked dominant genes conferring strong resistance. Characterisation of resistant Solanum accessions revealed both early and late oxidative bursts, highlighting dynamic defence signalling. These results confirm the heritability of resistance traits and underscore the genetic diversity within Solanum populations.