A revised nomenclature for ToxA haplotypes across multiple fungal species

Authors: ABOUKHADDOUR, REEM - Agriculture And Agri-Food Canada; HAFEZ, MOHAMED - Agriculture And Agri-Food Canada; MCDONALD, MEGAN - University Of Birmingham; MOFFAT, CAROLINE - Curtin University; NAVATHE, SSUDHIR - Banaras Hindu University; Friesen, Timothy; STRELKOV, STEPHEN - University Of Alberta; OLIVER, RICHARD - University Of Nottingham; TAN, KAR-CHUN - Curtin University; LIU, ZHAOHUI - North Dakota State University; MOOLHUIJZEN, PAULA - Curtin University; PHAN, HUYEN - Curtin University; SEE, PAO - Curtin University

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/17/2023
Publication Date: 2/21/2023
Citation: Aboukhaddour, R., Hafez, M., Mcdonald, M., Moffat, C., Navathe, S., Friesen, T.L., Strelkov, S., Oliver, R., Tan, K., Liu, Z., Moolhuijzen, P., Phan, H., See, P. 2023. A revised nomenclature for ToxA haplotypes across multiple fungal species. Phytopathology. https://doi.org/10.1094/PHYTO-01-23-0017-SC.
DOI: https://doi.org/10.1094/PHYTO-01-23-0017-SC

Interpretive Summary: ToxA is a virulence factor produced by at least three major pathogens of wheat causing tan spot, spot blotch, and septoria nodorum blotch of wheat and has therefore been the subject of several studies over the last 35 years. Confusion has risen due to inconsistencies in nomenclature, with some forms of ToxA being given multiple designations, making it difficult for current researchers to follow. The new nomenclature system presented here provides a logical naming system to be used in the future. Because this paper has invited input from all major researchers in the area, this nomenclature will be used by both pathologists and wheat geneticists in the future.

Technical Abstract: ToxA is a protein, a virulence factor, and one of the most studied necrotrophic effectors produced by plant pathogens. It is encoded by the single copy ToxA gene, which is present in numerous fungal species that cause leaf spot diseases on cereals worldwide. A recent rise in the identification and naming of ToxA haplotypes from species of the Pleosporales order by different research groups requires a standardization of this nomenclature. To date, 24 different ToxA haplotypes have been identified from four cereal leaf spot causing fungal pathogens. A summary of the identified ToxA haplotypes, and the proposed new nomenclature, is presented here from four fungal pathogens: Pyrenophora tritici-repentis, Parastagonospora nodorum, Parastagonospora pseudonodorum (formerly Parastagonospora avenaria f. sp. tritici) and Bipolaris sorokiniana. Most of the ToxA haplotypes to date have been reported in P. nodorum, and were found unique to this species, with the exception ofexcept for three haplotypes shared between P. nodorum and its sister species, P. pseudonodorum. Two of the ToxA haplotypes identified previously in P. nodorum have nonsense mutations, a stop codon in its sequence, rendering the ToxA genes un-functional. Here, we suggest to code each haplotype by the ToxA abbreviation followed by a sequential numerical value per haplotype in the chronological order of their identifications (ToxA#). The inactive haplotypes will be abbreviated by the small toxa to distinguish it them from the active form abbreviated by the capital ToxA#. #. Similarly, we suggest extending this nomenclature for ToxB, the P. tritici-repentis multi-copy gene encoding the chlorosis-inducing effector (ToxB). The ToxB gene has various homologs which are present in related and distantly related species. In that regard, a ToxB abbreviation followed by a sequential numerical value per haplotype (ToxB#) is suggested, and the inactive form will be codec by the small toxb#.