Effects of Genes Altering Calcium and Sterol Pathways in Plant-Nematode Interactions

Kamryn Stacy Clements

doi:10.7273/000007341

Plant parasitic nematodes (PPNs) are a major threat to agriculture due to their wide host range and worldwide distribution. Meloidogyne spp., otherwise known as root-knot nematodes (RKNs), are among the most prevalent. They significantly impact crops through the destruction of roots by the formation of galls and interception of nutrients. Chemical nematicides, though effective, are extremely harmful and in the process of being phased-out, therefore, research to develop other forms of resistance is urgent. This research focuses on understanding how the manipulation of two different areas of systems in Arabidopsis; calcium-dependent protein kinases (CPKs) and the sterol biosynthesis pathway, affects the nematode’s ability to infect and develop. CPKs are one of the earliest calcium sensing proteins and are vital to triggering signal cascades that allow the plant to initiate its immune responses. This study specifically targets CPK28, which is a negative regulator of P2K1, an extracellular ATP (eATP) receptor involved in various signal cascades. Three independent nematode assays using the mutant lines oxCPK28 “A”, oxCPK28 “E”, and cpk28-1, were conducted using Meloidogyne hapla in Arabidopsis thaliana. The results showed that differences in gene expression of CPK28 did not influence M. hapla parasitism. Furthermore, the sterol biosynthesis pathway was manipulated using Arabidopsis mutants to examine the effects these genes and phytosterols have on the nematode life cycle. Since nematodes do not produce their own sterols, they rely on the intake of sterols from their plant hosts. This study focuses on the characterization of 20 Arabidopsis mutants with genes altered in various levels of the pathway to determine which lines have potential use as genetic resistance options for RKN. Four independent nematode assays were conducted using Meloidogyne javanica with four different lines: CD-HMGROE “E”, CD-HMGROE “F”, fkj3158, and cvp1-3. The two independent lines CD-HMGROE “E” and CD-HMGROE “F” overexpress the HMG-CoA reductase 1 (HMGR1) enzyme which catalyzes the production of mevalonic acid (MVA), an important intermediate in sterol production. Despite the importance of this enzyme, overexpressing this gene did not result in altered M. javanica parasitism. The fkj3158 mutant possesses a point mutation in the FACKEL gene further downstream of HMGR1, which results in poor catalyzation by the FK C-14 Reductase enzyme. The impact this mutant has on the sterol biosynthesis pathway caused M. javanica second-stage juveniles (J2s) to progress slower from pre-feeding stages into feeding stages. Further downstream in the pathway is another major enzyme known as sterol methyltransferase 2 (SMT2). The cvp1-3 mutant has a point mutation in the gene encoding this enzyme, leading to a knockdown in its expression. The nematode assays with this mutant displayed increased parasitism by M. javanica. By studying these mutants, it is clear that the FACKEL and SMT2 genes are important in RKN parasitism. Future studies are needed to identify the specific sterol products made by these mutants, and more infection assays must be conducted with the rest of the lines characterized in this study. A greater understanding of the sterol biosynthesis in plant-nematode interactions is important, as it provides a promising pathway towards effective RKN resistance methods.

Effects of Genes Altering Calcium and Sterol Pathways in Plant-Nematode Interactions

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