Maize Leaf Epiphytic Bacteria Diversity Patterns Are Genetically Correlated with Resistance to Fungal Pathogen Infection

Abstract

Plant leaves host a specific set of microbial epiphytes. Plant genetic and solar UV-B radiation effects on the diversity of the phyllosphere were examined by measuring epiphytic bacterial ribosomal DNA diversity in a maize recombinant inbred (RI) mapping population. Several chromosomal quantitative trait loci (QTL) with significant effects on bacterial diversity were identified, some of which had effects only in the presence of UV-B radiation and others that had effects both with and without UV-B. Candidate genes with allele-specific effects were mapped to the bacterial diversity chromosomal regions. A glutamate decarboxylase candidate gene was located at a UV-B-specific chromosomal locus, and in a comparison between two RI lines with contrasting bacterial diversity phenotypes, high bacterial diversity was associated with high levels of glutamate decarboxylase enzyme activity, a component of the gamma-aminobutyric acid (GABA) pathway. The bacterial diversity loci exhibited a significant overlap with loci connected with Southern leaf blight (SLB) susceptibility in the field. A SLB-resistant inbred genotype had less beta bacterial diversity, and antibiotic treatment of inbreds increased this diversity. These results suggest that the GABA pathway is genetically associated with phyllosphere bacterial diversity. Furthermore, the colocalization of QTL between low bacterial diversity and fungal blight-resistance and the increase in beta diversity in antibiotic-treated leaves suggest that occupation of leaf habitats by a particular set of suppressive bacteria may restrict phyllosphere bacterial variability and increase resistance to fungal infection.

Canopy Light and Plant Health

“…1). UV-B radiation has also been reported to increase plant resistance to microbial pathogens (Gunasekera et al, 1997;Wargent et al, 2006;Gunasekera and Paul, 2007;Kunz et al, 2008;Demkura and Ballaré, 2012) and can interact with the plant to modify the composition of microbial communities in the phyllosphere (Kadivar and Stapleton, 2003;Balint-Kurti et al, 2010). Treatment with unnaturally high doses of UV-B radiation, or with UV wavelengths not present in the daylight spectrum (UV-C, l , 280 nm), has also been reported to activate defense-related pathways in several species (Bridge and Klarman, 1973;Brederode et al, 1991;Conconi et al, 1996;Mert-Turk et al, 2003;Glawischnig, 2007); however, the ecological significance of these responses is not clear.…”

Southern leaf blight disease severity is correlated with decreased maize leaf epiphytic bacterial species richness and the phyllosphere bacterial diversity decline is enhanced by nitrogen fertilization

“…The presence of multiple species in a single environment can allow for competitive exclusion of certain species (Meyer and Leveau, 2012). Balint-Kurti et al (2010) proposed that the presence of certain species of bacteria on corn leaves could increase resistance to C. heterostrophus infection. In their study, the more disease-susceptible B73 genotype leaves hosted fewer bacterial types with significantly more variation of the bacterial community.…”

Phyllosphere bacterial communities of trichome-bearing and trichomeless Arabidopsis thaliana leaves

“…The phyllosphere is colonized by various clades of microorganisms whose identity and functions are beginning to be unravelled (for reviews see Leveau 2006;Lindow and Brandl 2003). Factors shaping the phyllosphere microbiota are the availability of nutrients and water, air humidity and temperature, leaf surface topology, presence of epicuticular wax crystals, plant species, leaf age, leaf physiological status, the presence of wounds, and resistance to fungal pathogen infection (Marcell and Beattie 2002;Baldotto and Olivares 2008;Balint-Kurti et al 2010;Hunter et al 2010;Knief et al 2010a). Additionally, overall environmental conditions, availability of immigrant inoculum and the presence of trichomes have been suggested to be involved in determining the species composition of microbial populations on the plant surface (Beattie and Lindow 1999;Kinkel et al 2000).…”