Plant ‐specific lysin‐motif receptor‐like kinases (LysM‐RLKs) are implicated in the perception of We tested Compared with wild‐type plants, MtLYK9 thus has a dual role in plant immunity and the AM symbiosis, which raises questions about the functioning and the ancestral origins of such a receptor protein.
Lysin motif receptor–like kinases (LysM-RLKs) are involved in the perception of chitooligosaccharides (COs) and related lipochitooligosaccharides (LCOs) in plants. Expansion and divergence of the gene family during evolution have led to various roles in symbiosis and defense. By studying proteins of the LYR-IA subclass of LysM-RLKs of the Poaceae, we show here that they are high-affinity LCO-binding proteins with a lower affinity for COs, consistent with a role in LCO perception to establish arbuscular mycorrhiza (AM). In Papilionoid legumes, whole-genome duplication has resulted in two LYR-IA paralogs, MtLYR1 and MtNFP in Medicago truncatula, with MtNFP playing an essential role in root nodule symbiosis with nitrogen-fixing rhizobia. We show that MtLYR1 has retained the ancestral LCO-binding characteristic and is dispensable for AM. Domain swapping between the three LysMs of MtNFP and MtLYR1 and mutagenesis in MtLYR1 suggest that the MtLYR1 LCO-binding site is on the second LysM and that divergence in MtNFP led to better nodulation, but surprisingly with decreased LCO binding. These results suggest that divergence of the LCO-binding site has been important for the evolution of a role of MtNFP in nodulation with rhizobia.
more » « less- NSF-PAR ID:
- 10408983
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Plant And Cell Physiology
- ISSN:
- 0032-0781
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Summary N ‐acetyl glucosamine‐containing compounds, some of which are important signal molecules in plant−microbe interactions. Among these, both lipo‐chitooligosaccharides (LCOs) and chitooligosaccharides (COs) are proposed as arbuscular mycorrhizal (AM) fungal symbiotic signals. COs can also activate plant defence, although there are scarce data about CO production by pathogens, especially nonfungal pathogens.Medicago truncatula mutants in the LysM‐RLK MtLYK9 for their abilities to interact with the AM fungusRhizophagus irregularis and the oomycete pathogenAphanomyces euteiches . This prompted us to analyse whetherA. euteiches can produce COs.Mtlyk9 mutants had fewer infection events and were less colonised by the AM fungus. By contrast,Mtlyk9 mutants were more heavily infected byA. euteiches and showed more disease symptoms.Aphanomyces euteiches was also shown to produce short COs, mainly CO II, but also CO III and CO IV, and traces of CO V, bothex planta andin planta . -
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Summary Rhizobial lipochitooligosaccharidic Nod factors (NFs), specified by
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Stabb, Eric V. (Ed.)ABSTRACT Some soil bacteria, called rhizobia, can interact symbiotically with legumes, in which they form nodules on the plant roots, where they can reduce atmospheric dinitrogen to ammonia, a form of nitrogen that can be used by growing plants. Rhizobium-plant combinations can differ in how successful this symbiosis is: for example, Sinorhizobium meliloti Rm1021 forms a relatively ineffective symbiosis with Medicago truncatula Jemalong A17, but Sinorhizobium medicae WSM419 is able to support more vigorous plant growth. Using proteomic data from free-living and symbiotic S. medicae WSM419, we previously identified a subset of proteins that were not closely related to any S. meliloti Rm1021 proteins and speculated that adding one or more of these proteins to S. meliloti Rm1021 would increase its effectiveness on M. truncatula A17. Three genes, Smed_3503, Smed_5985, and Smed_6456, were cloned into S. meliloti Rm1021 downstream of the E. coli lacZ promoter. Strains with these genes increased nodulation and improved plant growth, individually and in combination with one another. Smed_3503, renamed iseA ( i ncreased s ymbiotic e ffectiveness), had the largest impact, increasing M. truncatula biomass by 61%. iseA homologs were present in all currently sequenced S. medicae strains but were infrequent in other Sinorhizobium isolates. Rhizobium leguminosarum bv. viciae 3841 containing iseA led to more nodules on pea and lentil. Split-root experiments with M. truncatula A17 indicated that S. meliloti Rm1021 carrying the S. medicae iseA is less sensitive to plant-induced resistance to rhizobial infection, suggesting an interaction with the plant’s regulation of nodule formation. IMPORTANCE Legume symbiosis with rhizobia is highly specific. Rhizobia that can nodulate and fix nitrogen on one legume species are often unable to associate with a different species. The interaction can be more subtle. Symbiotically enhanced growth of the host plant can differ substantially when nodules are formed by different rhizobial isolates of a species, much like disease severity can differ when conspecific isolates of pathogenic bacteria infect different cultivars. Much is known about bacterial genes essential for a productive symbiosis, but less is understood about genes that marginally improve performance. We used a proteomic strategy to identify Sinorhizobium genes that contribute to plant growth differences that are seen when two different strains nodulate M. truncatula A17. These genes could also alter the symbiosis between R. leguminosarum bv. viciae 3841 and pea or lentil, suggesting that this approach identifies new genes that may more generally contribute to symbiotic productivity.more » « less
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