Parasitic plants use virulence factors (VFs), including proteins, RNAs and small molecules, to successfully infect a host plant. To reach host cells, VFs must be released from parasite cells. In the case of proteinaceous VFs, one major determinant of secretion is the presence of an N-terminal secretion signal in the peptide sequence. Algorithms that predict this signal can identify the genome-wide set of putatively secreted proteins, called the ‘secretome’. Secretomes from fungal and nematode plant parasites have been extensively analysed and are rich in VFs. However, little attention has been paid to the secretomes of parasitic plants.
We conducted a comparative analysis of the secretomes of root (Striga spp.) and shoot (Cuscuta spp.) parasitic plants, to enable prediction of candidate VFs. Using orthogroup clustering and protein domain analyses we identified gene families/functional annotations that were common to both Striga and Cuscuta secretomes or were specific to either the Striga or Cuscuta secretomes. For example, Striga secretomes were strongly and uniquely associated with ‘PAR1’ protein domains, whereas Cuscuta secretomes had an abundance of ‘GMC oxidoreductase’ domains in their secretomes.
Genes encoding VFs are typically upregulated during host infection and establishment. Thus, we conducted transcriptional profiling of the secretome during infection for one of the most agriculturally damaging root parasitic weed of cereals, Striga hermonthica (see featured figure below). A significant portion of the Striga secretome was differentially expressed during early infection stages, which we probed further to identify genes following a ‘wave-like’ expression pattern peaking in the early penetration stage of infection. Within this set, we identified 39 genes encoding excellent candidate VFs with functions such as cell wall modification and potential immune suppression.
Full paper: https://doi.org/10.1186/s12870-024-04935-7