Mating type a locus alleles and genomic polymorphism in Sporisorium reilianum: comparison of sorghum isolates to those from maize
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2019, Australasian Plant Pathology Society Inc. Sporisorium reilianum causes head smut in sorghum and maize and 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, leading to a change from yeast-like to hyphal growth within the host plant. This switching is controlled through mating type loci. A total of 66 sorghum isolates of S. reilianum collected from fields in different geographic regions and 2 maize isolates were examined for mating compatibility, 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 to the corresponding components in maize, 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. To assay host preference in relationship to whole genome polymorphism, six amplified fragment length polymorphism (AFLP) selective primer combinations were used on DNA of S. reilianum isolates. High genetic polymorphism (61%) was observed between sorghum and maize isolates. 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.
