Under nutrient-limiting conditions, plants will enter into symbiosis with arbuscular mycorrhizal （AM） fungi for the enhancement of mineral nutrient acquisition from the surrounding soil. AM fungi live in close, intr...Under nutrient-limiting conditions, plants will enter into symbiosis with arbuscular mycorrhizal （AM） fungi for the enhancement of mineral nutrient acquisition from the surrounding soil. AM fungi live in close, intracellular association with plant roots where they transfer phosphate and nitrogen to the plant in exchange for carbon. They are obligate fungi, relying on their host as their only carbon source. Much has been discovered in the last decade concerning the signaling events during initiation of the AM symbiosis, including the identification of signaling molecules generated by both partners. This signaling occurs through symbiosis-specific gene products in the host plant, which are indispensable for normal AM development. At the same time, plants have adapted complex mechanisms for avoiding infection by pathogenic fungi, including an innate immune response to general microbial molecules, such as chitin present in fungal cell walls. How it is that AM fungal colonization is maintained without eliciting a defensive response from the host is still uncertain. In this review, we present a summary of the molecular signals and their elicited responses during initiation of the AM symbiosis, including plant immune responses and their suppression.展开更多
MYB34, MYB51, and MYB122 transcription factors are known as decisive regulators of indolic glucosinolate （IG） biosynthesis with a strong impact on expression of genes encoding CYP79B2 and CYP79B3 enzymes that redund...MYB34, MYB51, and MYB122 transcription factors are known as decisive regulators of indolic glucosinolate （IG） biosynthesis with a strong impact on expression of genes encoding CYP79B2 and CYP79B3 enzymes that redundantly convert tryptophan to indole-3-acetaldoxime （IAOx）. This intermediate represents a branching point for IG biosynthesis, and pathways leading to camalexin and indole-carboxylic acids （ICA）. Here we investigate how these MYBs affect the pathogen-triggered Trp metabolism. Our experiments indicated that these three MYBs affect not only IG production but also constitutive biosynthesis of other IAOx- derived metabolites. Strikingly, the PENETRATION 2 （PEN2）-dependent IG-metabolism products, which are absent in myb34/51/122 and pen2 mutants, were indispensable for full flg22-mediated induction of other IAOx-dedved compounds. However, germ induction and accumulation of ICAs and camalexin upon path- ogen infection was not compromised in myb34/51/122 plants, despite strongly reduced IG levels. Hence, in comparison with cyp79B2/B3, which lacks all IAOx-derived metabolites, we found myb34/51/122 an ideal tool to analyze IG contribution to resistance against the necrotrophic fungal pathogen Plectosphaerella cucumerina. The susceptibility of myb34/51/122 was similar to that of pen2, but much lower than susceptibility of cyp79B2/B3, indicating that MYB34/51/122 contribute to resistance toward P. cucumerina exclu- sively through IG biosynthesis, and that PEN2 is the main leaf myrosinase activating IGs in response to microbial pathogens.展开更多
基金Financial support for this research program was provided by the US National Science Foundation (IOS‐0842720)an award from the US National Science Foundation Graduate Research Fellowship (DGE‐1144153)
文摘Under nutrient-limiting conditions, plants will enter into symbiosis with arbuscular mycorrhizal （AM） fungi for the enhancement of mineral nutrient acquisition from the surrounding soil. AM fungi live in close, intracellular association with plant roots where they transfer phosphate and nitrogen to the plant in exchange for carbon. They are obligate fungi, relying on their host as their only carbon source. Much has been discovered in the last decade concerning the signaling events during initiation of the AM symbiosis, including the identification of signaling molecules generated by both partners. This signaling occurs through symbiosis-specific gene products in the host plant, which are indispensable for normal AM development. At the same time, plants have adapted complex mechanisms for avoiding infection by pathogenic fungi, including an innate immune response to general microbial molecules, such as chitin present in fungal cell walls. How it is that AM fungal colonization is maintained without eliciting a defensive response from the host is still uncertain. In this review, we present a summary of the molecular signals and their elicited responses during initiation of the AM symbiosis, including plant immune responses and their suppression.
文摘MYB34, MYB51, and MYB122 transcription factors are known as decisive regulators of indolic glucosinolate （IG） biosynthesis with a strong impact on expression of genes encoding CYP79B2 and CYP79B3 enzymes that redundantly convert tryptophan to indole-3-acetaldoxime （IAOx）. This intermediate represents a branching point for IG biosynthesis, and pathways leading to camalexin and indole-carboxylic acids （ICA）. Here we investigate how these MYBs affect the pathogen-triggered Trp metabolism. Our experiments indicated that these three MYBs affect not only IG production but also constitutive biosynthesis of other IAOx- derived metabolites. Strikingly, the PENETRATION 2 （PEN2）-dependent IG-metabolism products, which are absent in myb34/51/122 and pen2 mutants, were indispensable for full flg22-mediated induction of other IAOx-dedved compounds. However, germ induction and accumulation of ICAs and camalexin upon path- ogen infection was not compromised in myb34/51/122 plants, despite strongly reduced IG levels. Hence, in comparison with cyp79B2/B3, which lacks all IAOx-derived metabolites, we found myb34/51/122 an ideal tool to analyze IG contribution to resistance against the necrotrophic fungal pathogen Plectosphaerella cucumerina. The susceptibility of myb34/51/122 was similar to that of pen2, but much lower than susceptibility of cyp79B2/B3, indicating that MYB34/51/122 contribute to resistance toward P. cucumerina exclu- sively through IG biosynthesis, and that PEN2 is the main leaf myrosinase activating IGs in response to microbial pathogens.
