Host Specificity of Sporisorium reilianum Is Tightly Linked to Generation of the Phytoalexin Luteolinidin by Sorghum bicolor

Abstract

The smut fungus Sporisorium reilianum occurs in two varieties (S. reilianum f. sp. reilianum and S. reilianum f. sp. zeae) that cause head smut disease on sorghum and maize, respectively. Prior to plant infection, compatible haploid sporidia of S. reilianum fuse to form infectious dikaryotic hyphae that penetrate the leaf surface, spread throughout the plant, and reach the inflorescences, in which spore formation occurs. To elucidate the basis of host specificity of the two S. reilianum varieties, we compared disease etiology of S. reilianum f. sp. reilianum and S. reilianum f. sp. zeae on sorghum and maize. Both varieties could penetrate and multiply in both hosts. However, red spots appeared on inoculated leaves after sorghum infection with S. reilianum f. sp. zeae. Using matrix-assisted laser desorption-ionization time of flight analysis of leaf extracts, we show that sorghum reacts with the production of the red and orange phytoalexins luteolinidin and apigeninidin upon colonization by S. reilianum f. sp. zeae but not by S. reilianum f. sp. reilianum. Using in vitro growth assays, we demonstrate that luteolinidin but not apigeninidin slows vegetative growth of both S. reilianum f. sp. zeae and S. reilianum f. sp. reilianum. However, the phytoalexin biosynthesis gene SbDFR3 is only induced in sorghum after infection with S. reilianum f. sp. zeae, as shown by quantitative real-time polymerase chain reaction. This suggests that regulation of luteolinidin biosynthesis determines infection success of S. reilianum on sorghum.

Expression of Flavone Synthase II and Flavonoid 3′-Hydroxylase Is Associated with Color Variation in Tan-Colored Injured Leaves of Sorghum

“…The tan-colored sorghums accumulate relatively high levels of flavones (apigenin and luteolin) than red/purple colored sorghums (Siame et al, 1993; Dykes et al, 2009, 2011). Colored pigments are accumulated in response to infection with the fungi Bipolaris sorghicola (Kawahigashi et al, 2011; Mizuno et al, 2012), Colletotrichum sublineolum (Snyder and Nicholson, 1990), Cochliobolus heterostrophus (Aguero et al, 2002), Sporisorium reilianum (Zuther et al, 2012) or to wounding stress (Mizuno et al, 2014). Pigment accumulation is considered to enhance resistance to pathogen infection (Hipskind et al, 1990; Snyder and Nicholson, 1990; Lo et al, 1999; Clifford, 2000; Kawahigashi et al, 2011; Zuther et al, 2012).…”

SUPPRESSOR OF APICAL DOMINANCE 1 of Sporisorium reilianum Modulates Inflorescence Branching Architecture in Maize and Arabidopsis

“…zeae (SRZ) wild-type strains SRZ1_5-2 and SRZ2_5-1 (Schirawski et al, 2005;Zuther et al, 2012) and their deletion derivatives were used to inoculate potato dextrose broth (Difco) and grown at 28°C under constant shaking to an optical density at 600 nm (OD 600 ) of 0.5 to 0.8. Cell pellets were resuspended in water to reach an OD 600 of 2.0.…”

Molecular Variation of the Phytopathogenic Fungus Sporisorium reilianum in Valle del Mezquital, Hidalgo

“…Two varieties of S. reilianum have been described, based on host specificity; one that infects maize (SRZ) and another that infects sorghum (SRS) (Zuther et al, 2012). In relation to their sexual behavior, reference is made to the mating type locus that is composed of two unlinked genomic regions, a and b, that code for a pheromone, a pheromone receptor and homeodomain proteins.…”