The role of auxin in plant-parasitic nematode interactions

The plant parasitic cyst nematode Heterodera schachtii forms a specialised feeding cell in the roots of host plants. The feeding site, termed a syncytium, is the sole source of nutrition for the developing parasitic nematode. The initiation and development of a syncytium requires extensive re-programming of gene expression in the specific root cells selected by the nematode for feeding site initiation. Auxin is postulated to playa role in this re-differentiation process. Activation of the auxin-responsive promoter DR5 in syncytia indicates an increase in perceived auxin levels. To determine whether or not the increase in auxin is required for the formation of syncytia, auxin signalling mutants were infected with H. schachrii for analysis of syncytial and nematode development. Measuring the size of syncytia throughout H schachtii development revealed sign ificantly smaller syncytia were formed in the auxin signalling mutant, axrl-12 in comparison to wild type plants. To elucidate biological processes mediated by auxin during syncytial development in silico analysis was performed on syncytia transcriptome data; this was used to identify genes upregulated in the syncytia that contain auxin-responsive elements in the promoter region. The cytoplasmic contents of syncytia formed in axrl -12 and wild type plants were microaspirated; this material was used for qRT-PCR analysis of auxin responsive gene expression. qRT-PCR analysis revealed that genes encoding cell wall remodelling enzymes were differentially expressed in syncytia fonned on axr 1-12 plants. The effects of altered cell wall remodelling enzyme expression on the structure of syncytia were investigated by obtaining transverse sections through syncytia fanned in wild type and axr 1-12 plants. Monoclonal antibodies to defined glycans and a cellulose binding module were used to localise carbohydrate and structural protein components in the cell walls of syncytia. The carbohydrate components of syncytia were found to be similar but differences were observed in the expression of structural proteins in syncytia formed in axr1-J2 and wild type plants. Additionally, cell wall degradation had occurred more extensively in syncytia formed in wild type plants in comparison to syncytia in axrJ·12. Cell proliferation in axrJ-12 and wild type roots during syncytial development was examined and found to be reduced in the auxin signalling mutant, indicating a role for auxin mediating cell-cyc\e activation during the development of syncytia. This study provides the first insight into the biological processes mediated by auxin during the development of syncytia by H schachtii in Arabidopsis thaliana .EThOS - Electronic Theses Online ServiceGBUnited Kingdo