Doctoral Thesis
Towards understanding common mechanisms of nematode and aphid effectors in plant parasitism
Doctor of Philosophy (PhD), Murdoch University
2022
Abstract
Plant-parasitic nematodes and herbivorous insects are potent threats to sustainable agriculture: globally they cause broad-scale damage to crops and infest numerous plant species. Both of these groups are ‘sucking’ pests and secrete ‘effectors’ during parasitism. Effectors constitute pathogen proteins and small molecules that alter host-cell structure and function or aid in parasitism. Although there are many similarities in the way plant-parasitic nematodes and insects interact with their hosts, research on possible commonalities of effectors is lacking. The aim of this research was to study effectors that might be common between the two groups and then assess functional characterisation through RNAi.
Comparative bioinformatics was undertaken for in silico identification of putative common effectors in these pests. Thirteen target effectors were identified in silico including ESTs encoding for peroxiredoxin, annexin, calreticulin, chitinase, aspartyl protease, metalloprotease, thioredoxin, aminopeptidase, lipocalin, armet, cathepsin-l, glutathione peroxidase and glutathione s-transferase. Eight were used for functional characterisation through RNAi.
After in vitro RNAi in M. persicae, reproduction in nymphs fed on dsRNAs of crt, gst and gp was reduced by 50-70%, compared to no-dsRNA controls. During longer-term survival analysis aphids fed with dscrt, dsgst, dsgp and dsaxn survived only until days seven, six, five and ten, respectively.
In vitro RNAi for the eight target effector sequences in M. incognita led to a reduction in infectivity and reproduction. All treatments for silencing eight selected effector sequences led to reduced infection in the range of 42-80%. Similar levels of reduction in egg mass production were found in RKNs treated with dsRNA for axn, tdxn, gst, cpl and crt; where the reduction was 73% (axn), 76% (tdxn), 74% (gst), 73% (cpl) and 72% (crt), respectively.
For H. schachtii, soaking of J2s in dsRNA for all effector sequences except for dsamt led to a reduction in the number of cysts per gram dry weight, by 50 to 70% compared to the no-dsRNA and dsgfp controls. The greatest reduction was found for dsaxn, whereas dsamt fed J2s showed a 22% reduction, which was not statistically significant.
Details
- Title
- Towards understanding common mechanisms of nematode and aphid effectors in plant parasitism
- Authors/Creators
- Maria Maqsood
- Contributors
- Michael G. K. Jones (Supervisor) - Murdoch University, Centre for Crop and Food InnovationJohn Fosu-Nyarko (Supervisor) - Murdoch University, Centre for Crop and Food Innovation
- Awarding Institution
- Murdoch University; Doctor of Philosophy (PhD)
- Identifiers
- 991005585962207891
- Murdoch Affiliation
- State Agricultural Biotechnology Centre
- Resource Type
- Doctoral Thesis
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