Presentation Information
[4GteX-03]Isoflavone Catabolic Network in Soybean Root-Associated Bacteria and Its Effects on Plant-Microbe Interactions
○Tomoaki Sato1 (1. RISH, Kyoto Univ. (Japan))
Keywords:
Soybean rhizosphere,Secondary metabolite,Isoflavone,Plant-Microbe Interaction
The rhizosphere is defined as the area of soil affected by plant roots and serves as a region of active plant-microbe interactions. Plants secrete up to one-fifth of the carbon fixed through photosynthesis into the rhizosphere as root exudates. Root exudates contain primary metabolites such as sugars and amino acids, as well as secondary metabolites. Recent studies have shown that plants shape host-specific rhizosphere microbiota through these secondary metabolites1, 2, 3). Furthermore, the ability of bacteria to metabolize these compounds is considered crucial for microbiota assembly; however, the underlying mechanisms remain largely unknown.
Isoflavones are secondary metabolites secreted from soybean roots. Daidzein, a major isoflavone, increases the abundance of Comamonadaceae, a dominant bacterial family in the soybean rhizosphere, indicating that isoflavones are involved in shaping the soybean rhizosphere microbiota. We previously isolated daidzein-degrading bacteria belonging to the family Comamonadaceae from soybean roots and discovered the isoflavone catabolism (ifc) gene cluster responsible for the oxidative catabolism of daidzein4). In this study, we extended the analysis of bacterial degradation characteristics to three isoflavones secreted into the soybean rhizosphere (daidzein, genistein, and glycitein) to elucidate the isoflavone metabolic network and how bacterial metabolic ability affects plant-microbe interactions.
We conducted an isoflavone degradation assay using nine strains of Comamonadaceae isolated from soybean roots. Although most strains did not degrade glycitein, a few did, highlighting strain-specific degradation abilities. These strains did not completely degrade glycitein but instead converted it into a novel intermediate in the ifc pathway. We also demonstrated a previously uncharacterized enzymatic function responsible for this conversion. Furthermore, microbial community analysis using an in vitro pseudo-rhizosphere system showed that the glycitein-derived ifc intermediate shaped a soil microbial community structure distinct from that shaped by glycitein. Based on these results, we propose that microbial-transformed plant secondary metabolites may contribute to the formation of more complex plant-microbe interactions.
1) Okutani et al., 2020. Rhizosphere modelling reveals spatiotemporal distribution of daidzein shaping soybean rhizosphere bacterial community. Plant Cell and Environment.
2) Nakayasu et al., 2021. Tomato roots secrete tomatine to modulate the bacterial assemblage of the rhizosphere. Plant Physiology.
3) Shimasaki et al., 2021. Tobacco root endophytic Arthrobacter harbors genomic features enabling the catabolism of host-specific plant specialized metabolites. mBio.
4) Aoki, Shimasaki et al., 2024. An isoflavone catabolism gene cluster underlying interkingdom interactions in the soybean rhizosphere. ISME Communications.
Isoflavones are secondary metabolites secreted from soybean roots. Daidzein, a major isoflavone, increases the abundance of Comamonadaceae, a dominant bacterial family in the soybean rhizosphere, indicating that isoflavones are involved in shaping the soybean rhizosphere microbiota. We previously isolated daidzein-degrading bacteria belonging to the family Comamonadaceae from soybean roots and discovered the isoflavone catabolism (ifc) gene cluster responsible for the oxidative catabolism of daidzein4). In this study, we extended the analysis of bacterial degradation characteristics to three isoflavones secreted into the soybean rhizosphere (daidzein, genistein, and glycitein) to elucidate the isoflavone metabolic network and how bacterial metabolic ability affects plant-microbe interactions.
We conducted an isoflavone degradation assay using nine strains of Comamonadaceae isolated from soybean roots. Although most strains did not degrade glycitein, a few did, highlighting strain-specific degradation abilities. These strains did not completely degrade glycitein but instead converted it into a novel intermediate in the ifc pathway. We also demonstrated a previously uncharacterized enzymatic function responsible for this conversion. Furthermore, microbial community analysis using an in vitro pseudo-rhizosphere system showed that the glycitein-derived ifc intermediate shaped a soil microbial community structure distinct from that shaped by glycitein. Based on these results, we propose that microbial-transformed plant secondary metabolites may contribute to the formation of more complex plant-microbe interactions.
1) Okutani et al., 2020. Rhizosphere modelling reveals spatiotemporal distribution of daidzein shaping soybean rhizosphere bacterial community. Plant Cell and Environment.
2) Nakayasu et al., 2021. Tomato roots secrete tomatine to modulate the bacterial assemblage of the rhizosphere. Plant Physiology.
3) Shimasaki et al., 2021. Tobacco root endophytic Arthrobacter harbors genomic features enabling the catabolism of host-specific plant specialized metabolites. mBio.
4) Aoki, Shimasaki et al., 2024. An isoflavone catabolism gene cluster underlying interkingdom interactions in the soybean rhizosphere. ISME Communications.
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