Mating type a locus alleles and genomic polymorphism in Sporisorium reilianum: Comparison of sorghum isolates to those from maize

Authors: RADWAN, GHADA - Texas A&M University; Prom, Louis; ODVODY, GARY - Texas A&M Agrilife; MAGILL, CLINT - Texas A&M University

Submitted to: Australasian Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/23/2018
Publication Date: 3/1/2019
Citation: Radwan, G., Prom, L.K., Odvody, G., Magill, C. 2019. Mating type a locus alleles and genomic polymorphism in Sporisorium reilianum: Comparison of sorghum isolates to those from maize. Australasian Plant Pathology. 48(2):119-129. https://doi.org/10.1007/s13313-018-0607-3.
DOI: https://doi.org/10.1007/s13313-018-0607-3

Interpretive Summary: Sorghum head smut is an important fungus disease that can cause total yield loss in fields that are severely infected. The fungal pathogen also causes head smut on maize (corn). Infection requires the formation of a fungal body resulting from the combination of two compatible mating types. In this study, isolates of the head smut pathogen were collected from sorghum and maize fields in different geographic regions and tested for mating. The work showed a mating compatibility between maize and sorghum isolates; however, isolates from maize were grouped in one cluster while those collected from sorghum were grouped into four clusters, indicating genetic differentiation between the different hosts exists. The results suggest that more research may be needed to determine the effect of head smut on sorghum yield when planted in fields previously planted with maize.

Technical Abstract: Sporisorium reilianum is a dimorphic biotrophic phytopathogenic fungus that causes head smut in sorghum and maize. The pathogen exists in two formae speciales (Sporisorium reilianum f. sp. reilianum and Sporisorium reilianum f. sp. Zeae) that have preference for sorghum and maize, respectively. Infection requires the formation of a dikaryon between sporidia of compatible mating types and leads to a change from yeast-like to hyphal growth within the host plant. This switching is controlled through mating type loci. Isolates of S. reilianum collected from sorghum and maize fields in different geographic regions were tested for mating. A total of 120 pairs were examined, leading to the establishment of haploid cultures with three different alleles at the a mating type locus, as verified by gene expression. Interestingly, a mating compatibility was detected between maize and sorghum isolates. Comparison of amino acid sequences, deduced from nucleotide sequencing of pheromone precursor genes of sorghum isolates to the corresponding components in maize isolates, showed 100% similarity of pheromone components mfa1.2, mfa2.1, mfa3.1 and 97% for mfa1.3, mfa3.2 and mfa2.3. Only 1 amino acid substitution was detected in sorghum mfa1.3 as compared to that of maize, specifically an isoleucine to leucine change. To assay host preference in relationship to whole genome polymorphism, six amplified fragment length polymorphism (AFLP) selective primer combinations were used on DNA of thirty S. reilianum isolates. High genetic polymorphism (61%) was observed between isolates from maize and those from sorghum. The resultant dendrogram constructed using neighbor-joining (NJ) analysis grouped maize isolates into one cluster with high similarity (>88%) while sorghum isolates grouped into four clusters suggesting that genetic differentiation contributes to host specific populations of S. reilianum.