Simpfendorfer, S. | bioRxiv Science

bioRxiv2020

Genetic Variance for Fusarium Crown Rot Tolerance in Durum Wheat

Tolerance to the cereal disease Fusarium crown rot (FCR) was investigated in a set of 34 durum wheat genotypes, with Suntop, (bread wheat) and EGA Bellaroi (durum) as tolerant and intolerant checks, in a series of replicated field trials over four years with inoculated (FCR-i) and non-inoculated (FCR-n) plots of the genotypes. The genotypes included conventional durum lines and lines derived from crossing durum with 2-49, a bread wheat line with the highest level of partial resistance to FCR. A split plot trial design was chosen to optimize the efficiency for the prediction of FCR tolerance for each genotype. A multi-environment trial (MET) analysis was undertaken which indicated that there was good repeatability of FCR tolerance across years. Based on an FCR tolerance index, Suntop was the most tolerant genotype and EGA Bellaroi was very intolerant, but many durum wheats had FCR tolerance indices which were comparable to Suntop. These included some conventional durum lines, V101030, TD1702, V11TD013*3X-63 and DBA Bindaroi, as well as genotypes from crosses with 2-49 (V114916 and V114942). The correlation between FCR tolerance and FCR-n yield predictions was moderately negative indicating it could be somewhat difficult to develop high yielding FCR-tolerant genotypes. However, FCR tolerance showed a positive correlation with FCR-i yield predictions in seasons of high disease expression indicating it could be possible to screen for FCR tolerance using only FCR-i treatments. These results are the first demonstration of genetic diversity in durum germplasm for FCR tolerance and they provide a basis for breeding for this trait.

plant biology↗

bioRxiv2019

Transposon mediated horizontal transfer of the host-specific virulence protein ToxA between three fungal wheat pathogens

Most known examples of horizontal gene transfer (HGT) between eukaryotes are ancient. These events are identified primarily using phylogenetic methods on coding regions alone. Only rarely are there examples of HGT where non-coding DNA is also reported. The gene encoding the wheat virulence protein ToxA and surrounding 14 kb is one of these rare examples. ToxA has been horizontally transferred between three fungal wheat pathogens (Parastagonospora nodorum, Pyrenophora tritici-repentis and Bipolaris sorokiniana) as part of a conserved [~]14kb element, which contains coding and non-coding regions. Here we use long-read sequencing to define the extent of HGT between these three fungal species. Construction of near-chromosomal level assemblies enabled identification of terminal inverted repeats on either end of the 14kb region, typical of a Type II DNA transposon. This is the first description of ToxA with complete transposon features, which we call ToxhAT. In all three species, ToxhAT resides in a large (140-250 kb) transposon-rich genomic island which is absent in toxA- isolates. We demonstrate that the horizontal transfer of ToxhAT between Pyrenophora tritici-repentis and P. nodorum occurred as part of a large [~]80kb HGT which is now undergoing extensive decay. In contrast, in B. sorokiniana ToxhAT and its resident genomic island are mobile within the genome. Together these data provide insight into the non-coding regions that facilitate HGT between eukaryotes and the genomic processes which mask the extent of HGT between these species.\n\nIMPORTANCEThis work dissects the tripartite horizontal transfer of ToxA; a gene that has a direct negative impact on global wheat yields. Defining the extent of horizontally transferred DNA is important because it can provide clues as to the mechanisms that facilitate HGT. Our analysis of ToxA and its surrounding 14kb suggests that this gene was horizontally transferred in two independent events, with one event likely facilitated by a Type II DNA transposon. These horizontal transfer events are now in various processes of decay in each species due to the repeated insertion of new transposons and subsequent rounds of targeted mutation by a fungal genome defense mechanism known as repeat induced point-mutation. This work highlights the role that HGT plays in the evolution of host adaptation in eukaryotic pathogens. It also increases the growing body of evidence that transposons facilitate adaptive HGT events between fungi present in similar environments and hosts.\n\nDATA AVAILABILITYAll raw sequencing data is available under NCBI BioProject PRJNA505097.\n\nThe P. nodorum SN15 Whole Genome Shotgun project has been deposited at DDBJ/ENA/GenBank under the accession SSHU00000000. The version SSHU01000000 is described in this paper. The P. nodorum SN79-1087 Whole Genome Shotgun project has been deposited under the accessions CP039668-CP039689. The Whole Genome shotgun project and accession numbers for B. sorokiniana isolates are as follows: CS10; SRZH00000000, CS27; SRZG00000000, WAI2406; SRZF00000000, WAI2411; SRZE00000000. Transposon annotations, CS10 and CS27 gene annotations are available at https://github.com/megancamilla/Transposon-Mediated-transfer-of-ToxA

genomics↗