Host specificity in Sporisorium reilianum is determined by distinct mechanisms in maize and sorghum

Abstract

Smut fungi are biotrophic plant pathogens that exhibit a very narrow host range. The smut fungus Sporisorium reilianum exists in two host-adapted formae speciales: S. reilianum f. sp. reilianum (SRS), which causes head smut of sorghum, and S. reilianum f. sp. zeae (SRZ), which induces disease on maize. It is unknown why the two formae speciales cannot form spores on their respective non-favoured hosts. By fungal DNA quantification and fluorescence microscopy of stained plant samples, we followed the colonization behaviour of both SRS and SRZ on sorghum and maize. Both formae speciales were able to penetrate and multiply in the leaves of both hosts. In sorghum, the hyphae of SRS reached the apical meristems, whereas the hyphae of SRZ did not. SRZ strongly induced several defence responses in sorghum, such as the generation of H2 O2 , callose and phytoalexins, whereas the hyphae of SRS did not. In maize, both SRS and SRZ were able to spread through the plant to the apical meristem. Transcriptome analysis of colonized maize leaves revealed more genes induced by SRZ than by SRS, with many of them being involved in defence responses. Amongst the maize genes specifically induced by SRS were 11 pentatricopeptide repeat proteins. Together with the microscopic analysis, these data indicate that SRZ succumbs to plant defence after sorghum penetration, whereas SRS proliferates in a relatively undisturbed manner, but non-efficiently, on maize. This shows that host specificity is determined by distinct mechanisms in sorghum and maize.

The ‘PhenoBox’, a flexible, automated, open‐source plant phenotyping solution

“…Head smut fungi, which infect crops such as barley, maize and sugar cane in addition to the model grass Brachypodium distachyon, cause distinctive symptoms in the form of spore-filled sori only in the floral organs of their grass hosts (Laurie et al, 2012;Poloni & Schirawski, 2016;Rabe et al, 2016). During the host's vegetative phase, the fungal pathogen causes no distinctive symptoms, reminiscent of plant endophytesorganisms that colonize plant tissue without causing apparent disease.…”

Stenocarpella maydis and Sporisorium reilianum: Two Pathogenic Fungi of Maize

“…zeae compared with that of S. reilianum f. sp. reilianum, showing that host specificity is determined by different mechanisms in sorghum and maize [8][9]. This fungus is an inhabitant of the soil where it can survive up to 10 years in the form of a teliospore: a structure generated by fragmentation of the mycelium in plant tissues either on the tassels or in the corn cob.…”

Screening of Secreted Proteins of Sporisorium reilianum f. sp. zeae for Cell Death Suppression in Nicotiana benthamiana

“…Prior to plant infection, compatible haploid sporidia form conjugation hyphae that grow toward each other and fuse at their tips (Schirawski et al, 2005). After mating, the fungus then grows as dikaryotic hyphae that penetrate and colonize the plant initially without causing severe symptoms (Martinez et al, 1999;Prom et al, 2011;Poloni and Schirawski, 2016). Symptoms become evident only at the flowering time when spore formation and phyllody occur in the inflorescences (Wilson and Frederiksen, 1970;Martinez et al, 1999;Ghareeb et al, 2011;Poloni and Schirawski, 2016).…”