Circadian rhythms are daily rhythms in gene expression and physiology with a period of approximately 24 hours. Despite the knowledge of circadian rhythms in animals, plants, fungi and cyanobacteria, the circadian biology of one of the most economically important groups of organisms remains almost completely unstudied: rhizobacteria. PAS domains are found in circadian clock components in a number of kingdoms of life. Several PAS domain-coding genes exist in the rhizobacterium Bacillus subtilis, with ytvA being one and also a blue light photoreceptor. Here I used bioluminescence timecourse imaging experiments to measure ytvA promoter activity in transgenic B. subtilis, following inoculation onto the roots of plants entrained to opposite light regimes. Results showed ytvA promoter activity oscillated with a period of approximately 24 h, indicating that circadian rhythms in Arabidopsis host plants may provide cues to entrain B. subtilis cultures. In experiments investigating the influence of oppositely-entrained B. subtilis on expression of the Arabidopsis clock gene CCA1, I found cultures lit during the day lengthened CCA1 period and cultures lit during the night shortened CCA1 period. This may suggest B. subtilis can in turn affect plant circadian clock function. This preliminary study provides the first evidence for the potential bidirectional signalling of circadian timing information between plants and bacteria, building on previous work demonstrating the effects of the rhizosphere on plant circadian clock function. Future work should seek to refine bacterial entrainment regimes, uncover bacterial clock genes and pinpoint entrainment signals involved in this interaction. Studying rhythmicity in rhizobacteria may also require the use of complex intact soil microbiomes instead of single-species experiments. Understanding the functioning of bacterial circadian clocks and their interactions with host plants has implications for the use of bacteria in industry, the treatment of microbe-associated diseases and the use of rhizobacteria in agriculture.
|Date of Award||1 Oct 2019|
- The University of Bristol
|Supervisor||Antony N Dodd (Supervisor) & Keara A Franklin (Supervisor)|