Demonstrating Natural Variation in Circadian Clock Traits in Medicago truncatula
The circadian clock is an essential oscillator in the cells of organisms of all domains of life. For plants, the circadian clock has a hand in coordinating time-of-day responses to abiotic and biotic stress, as well as optimizing photosynthetic efficiency and accurately timing flowering (McClung, R., 2006). Medicago truncatula, the model legume, is a well studied species which forms associations with soil rhizobia for nitrogen fixation (Rose, J., 2008). It has previously been shown that the circadian clock in M. truncatula controls metabolism closely linked to root nodule formation (Achom, M., et. al, 2022). However, the genes regulating the circadian clock in this species remain vastly unidentified. One way to identify candidate genes associated with circadian function is to run a genome wide association study (GWAS) on a population which demonstrates variation in circadian phenotype. For this, the variation must first be demonstrated within available accessions. To screen the circadian traits, we conducted a leaf-movement study on 240 accessions of M. truncatula. We entrained seedlings of M. truncatula to a 12 hour light dark cycle. Following this, we imaged the seedlings every 20 minutes for three days in constant light and temperature conditions, to capture the circadian driven leaf movement. Using the stacks of images created, we ran the Tracking Rhythms in Plants (TRiP) pipeline in Python to estimate the circadian period length of each individual plant. Ultimately, we were able to identify natural variation within the circadian period lengths of the ecotypes tested. We also demonstrated that the circadian period lengths of M. truncatula are exceptionally long (between 27 and 29 hours) as compared to other species. Our next steps are to perform GWAS to identify candidate genes underlying the circadian variation to resolve more about the circadian clock of M. truncatula.