Systemic virus‐induced gene silencing allows functional characterization of maize genes during biotrophic interaction with Ustilago maydis

Abstract

Summary• Infection of maize (Zea mays) plants with the corn smut fungus Ustilago maydis leads to the formation of large tumors on the stem, leaves and inflorescences. In this biotrophic interaction, plant defense responses are actively suppressed by the pathogen, and previous transcriptome analyses of infected maize plants showed massive and stage-specific changes in host gene expression during disease progression.• To identify maize genes that are functionally involved in the interaction with U. maydis, we adapted a virus-induced gene silencing (VIGS) system based on the brome mosaic virus (BMV) for maize. Conditions were established that allowed successful U. maydis infection of BMV-preinfected maize plants. This set-up enabled quantification of VIGS and its impact on U. maydis infection using a quantitative real-time PCR (qRT-PCR)-based readout.• In proof-of-principle experiments, an U. maydis-induced terpene synthase was shown to negatively regulate disease development while a protein involved in cell death inhibition was required for full virulence of U. maydis.• The results suggest that this system is a versatile tool for the rapid identification of maize genes that determine compatibility with U. maydis.

Discovery, Biosynthesis and Stress-Related Accumulation of Dolabradiene-Derived Defenses in Maize

“…ZmAN2 was first described in a differential display analysis of highly elicited transcripts following F. graminearum challenge of maize silks (Harris et al, 2005). Following the first description of ZmAN2, pathogen-elicited transcripts have been observed and reported in a large number of maize studies with diverse microbes Schmelz et al, 2011Schmelz et al, , 2014van der Linde et al, 2011;Vaughan et al, 2014;Christie et al, 2017). The nearly ubiquitous presence of ZmAN2 as a pathogen defense transcript marker is consistent with the essential biosynthetic role in the modular formation of multiple specialized diterpenoid metabolites, including not only A-and B-series kauralexins but also dolabralexins.…”

The rice <i>GRH2</i> and <i>GRH4</i> activate various defense responses to the green rice leafhopper and confer strong insect resistance

“…These results suggest that GRH infestation induces the production of sesquiterpenes in the resistant line TGRH29. The accumulation of pathogen-induced sesquiterpenoid phytoalexins has a direct positive relationship with the transcript levels of Tps6 and Tps11 (Huffaker et al 2011), and plants in which these genes are silenced exhibit increased susceptibility to Ustilago maydis (van der Linde et al 2011). Further studies using the loss-of-function lines in which the expression of TPS genes is suppressed are needed to elucidate the biological role of rice TPS genes in GRH resistance.…”

Signals that stop the rot: Regulation of secondary metabolite defences in cereals

“…Likewise, zealexin production is preceded by increased expression of the biosynthetic genes Tps6/11 [28]. Expression of both the Tps6 and Tps11 alleles have also been stimulated following U. maydis infection [18] and when silenced using VIGS, plants are more susceptible to U. maydis [103]. Taken together, these results propose that the plant hormones JA and Et mediate production of terpenoid phytoalexins and thereby defence in maize (Table 1).…”