Systemic enrichment of antifungal traits in the rhizosphere microbiome after pathogen attack

Abstract

Summary Plant‐associated microbial communities are crucial for plant growth and play an important role in disease suppression. Community composition and function change upon pathogen attack, yet to date, we do not know whether these changes are a side effect of the infection or actively driven by the plant. Here, we used a split‐root approach to test whether barley plants recruit bacteria carrying antifungal traits upon infestation with Fusarium graminearum. Split‐root systems allow disentangling local infection effects, such as root damage, from systemic, plant‐driven effects on microbiome functionality. We assessed the recruitment of fluorescent pseudomonads, a taxon correlated with disease suppression, and of two well‐described antifungal genes (phlD coding for 2,4‐DAPG and hcnAB coding for HCN). We show an enrichment of fluorescent pseudomonads, phlD and hcnAB, upon pathogen infection. This effect was only measurable in the uninfected root compartment. We link these effects to an increased chemotaxis of pseudomonads towards exudates of infected plants. Synthesis. We conclude that barley plants selectively recruited bacteria carrying antifungal traits upon pathogen attack and that the pathogen application locally interfered with this process. By disentangling these two effects, we set the base for enhancing strategies unravelling how pathogens and plant hosts jointly shape microbiome functionality.

Influence of different biological control agents and compost on total and nitrification-driven microbial communities at rhizosphere and soil level in a lettuce -Fusarium oxysporumf. sp.lactucaepathosystem

“…A remarkable result of this study concerns the high abundance that was observed in the rhizosphere samples of the phlD and hcnAB genes known to encode the production of antifungal compounds such as 2,4‐diacetylphloroglucinol (DAPG) and HCN (Dudenhoffer et al . ). We speculated that Pseudomonas sp.…”

Understanding and exploiting plant beneficial microbes

“…This could represent a general response to the plant defense mechanisms, but may also reflect changes made to the habitat by the pathogen [85,86]. Antifungal traits are enriched in barley following infection with Fusarium graminearum , potentially via changes in exudate composition [87]. A study of tomato plants challenged with the pathogen Ralstonia solanacearum revealed that the root exudation profile changed upon pathogen infection, increasing the secretion of phenolic compounds.…”

Surviving in a Hostile World: Plant Strategies to Resist Pests and Diseases

“…Plants control their rhizosphere microbiome through root exudates (34,107,119), which change the chemical composition of the rhizosphere to attract and support beneficial microbes, such as plant growth-promoting rhizobacteria (PGPR) and mycorrhizal fungi (Figure 5) (59,129). Pests and diseases are known to alter root exudation composition, which can result in changes in soil-and root-associated microbiomes (11,46,68). Although the exact mechanisms driving these stress-induced changes remain unclear, key defense signaling chemicals, including SA, JA, and benzoxaxinoids, have been shown to influence microbial communities in the rhizosphere (26,58,73).…”

“…Although the exact mechanisms driving these stress-induced changes remain unclear, key defense signaling chemicals, including SA, JA, and benzoxaxinoids, have been shown to influence microbial communities in the rhizosphere (26,58,73). Microbes recruited to roots of pathogen-or herbivore-infested plants can contribute to defense via both direct mechanisms, such as biocidal activity against the attackers (46,68), and indirect mechanisms, such as competition for nutrients or induction of AR (11, 151) ( Figure 5). Stress-induced changes in root exudation can also benefit the progeny of the attacked plant.…”