Sienna Casciato ‘22
Major: Biology
Affiliations: MARC Fellow, Sandy Stewart Undergraduate Research Grant Recipient

Faculty Mentor: Dr. Kwangwon Lee, Associate Professor of Biology


Photoperiodism is a physiological response of an organism to changes of the ambient environment over a year and plays a major role in fitness of an organism in nature. There are two theories that explain how photoperiodism and a related process, the circadian rhythm, may be related. The first theory is called the external coincidence hypothesis, and the second theory is called the internal coincidence hypothesis. Unlike the mechanism of photoperiodism, that of the circadian rhythm (24-hour cycles within an organism) is well characterized. We hypothesized that there are multiple genes that are involved in photoperiodism, and that the genes involved in the circadian clock might also be involved in photoperiodism. To test our hypotheses, we developed the protoperithecia assay (PPA). Protoperithecia is a female sexual reproductive structure in N. crassa and is known to be responsive to different photoperiods. This data was used as the readout for an organism’s ability to determine the day-length. We performed Quantitative Trait Loci (QTL) analysis on the number of protoperithecia at different photoperiods using 91 F1 progeny of N. crassa. We found a major QTL on chromosome (Chr) 5, and multiple minor QTLs on other Chr. We characterized 21 knockout mutants in the target region of Chr 5 and 17 knockout mutants on one minor QTL in Chr 1. We found two candidate genes for measuring day-length. One is FGSC 17264 on Chr 5, and the other is FGSC 11617 on Chr 1. We also performed PPA on 10 known clock/photoreceptor mutants to test our hypothesis that the circadian clock is involved in photoperiodism. We found one candidate gene, FGSC 12467. Our data support the view that the circadian clock is a part of the day-length measuring mechanism. Our data also supported the hypothesis that there are multiple genes involved in photoperiodism because we identified 2 candidate genes in total that may be involved in measuring photoperiod in N. crassa. The current study will provide a comprehensive view on the possible genetic mechanisms of photoperiodism.