Abstract: During root nodulation both the rhizobial symbiont and the legume host must coordinate resources to ensure proper growth and maintenance of the symbiotic relationship. To determine if the provision of amino acids across symbiotic membranes is required to establish and maintain symbiosis we examined the role of the Usually Multiple Amino acids Move In and out Transporter (UmamiT) family¹. In addition to a previously published MtUmamiT14² we identified several Medicago truncatula UmamiTs that show strong expression in a nodulation context^3,4,5_, which are candidates for either rhizobial feeding or assimilate transport. Using transcriptome analysis we showed that UmamiT nodulins 1, 2, & 6 (UTN1/2/6) are expressed in root hairs⁴ within hours of inoculation⁵ indicating a likely role in rhizobial feeding during the infection stages. Localisation using promoter:GUS constructs suggested that UTN1, 2, 3, & 6 localised to infection associated zones and internal vasculature in mature nodules. Phylogenetic analysis indicated that UTN1 and UTN2 are phylogenetically distinct from UTN3-7, which appear to be part of a large legume-specific gene radiation covering both determinate and indeterminate nodulators. Many of the UTN orthologues in other legumes were similarly expressed throughout nodulation^6,7,8 indicating a likely conserved function across legumes. Amino acid transport was confirmed using the Xenopus laevis oocyte heterologous expression system. To determine the importance of these symbiosis-associated UmamiTs, we generated UTN1/2/6 triple mutants via CRISPR which show an impaired infection phenotype indicating the action of these UTNs is important to the establishment of infection. Further work is necessary to identify complete substrate capacity and subcellular localisation, as well as the effect of symbiosis-associated UmamiTs to nitrogen provision to the plant as a whole.

References

1. Ladwig, F., et al (2012). Plant Physiology, 158, 1643–1655
2. Garcia, K., et al (2023). Scientific Reports, 13, 804
3. Roux, B., et al (2014) The Plant Journal, 77: 817-837
4. Jardinaud, MF., et al (2016). Plant Physiology, 171, 2256–2276,
5. Larrainzar, E., et al (2015). Plant physiology, 169,.233-26
6. Ye, Q., et al (2022) Molecular Plant, 15, 1852–1867
7. Liu, Z., et al (2023) Nature Communications, 9, 515–524
8. Frank, M., et al (2022). BioRxiv, doi.org/10.1101/2022.12.23.521739

Biography: I studied immunology and genetics as an undergraduate at ANU before heading to the University of Sydney for Honours in structural biochemistry. While the knowledge I obtained there was inordinately useful, I realised I wanted to work with something a bit more tangible and, if at all possible, avoid cell culture. This lead me to return to ANU to specialise into plant science with a Master’s degree. I then began my PhD in the Djordjevic and former Martin labs straddling the border between BSB and Plant Science. This allowed me to combine my love of molecular biology and my new-found plant lore into a project that saw me using a wide array of tools and techniques, from frog husbandry and oocyte work, to a foray into phylogenetics and CRISPR mutagenesis.