(300-97) Synergy and complexity in the Autoregulation of Nodulation MtTML1 and MtTML2 and DAR hypernodulation mutants add new insights to regulation of nodulation
Alumni Distinguished Professor of Genetics Clemson University Clemson, South Carolina
Body of Abstract: The legume/rhizobia nitrogen-fixing symbiosis is tightly regulated by the plant partner, based on available soil nitrogen and the plant’s needs. Using reverse and forward genetic approaches, we report new genes and interactions in the Autoregulation of Nodulation (AON) pathway. A single protein, TML (TOO MUCH LOVE), functions in Lotus japonicus roots to maintain susceptibly to rhizobial infection and also control the number of nodules formed. Medicago truncatula has two sequence homologs of LjTML, MtTML1 and MtTML2. We used reverse genetics to generate stable single and double mutants harboring multiple allelic variations in these genes. Plants containing single TML mutations made approximately 2x more nodules than the wild type plants while plants containing both mutations nodulated up to 20x more than the wild type plants. The two genes have different spatial and temporal patterns of expression during the first 72 hours post inoculation. Additional phenotyping of the plants including nodule number when grown in nitrogen sufficient conditions, expression analysis in single mutants and analysis of segregating populations suggest the total combined expression level of the two genes may be correlated with phenotype and suggest complexity in the role of both TMLs in M. truncatula nodule number regulation. We also identified a new gene by forward genetics, dar (defective in auto regulation) that also hypernodulates and has altered TML expression among other phenotypes. DAR encodes a conserved integral membrane protein with five transmembrane domains, part of a small protein family with six members in M. truncatula. We discuss how these mutants can be used in pathway analysis to understand AON. Supported by NSF IOS #1444461 and 1733470.