Timing for outcrossing : circadian clock regulates floral rhythms with large fitness consequences
Like most organisms, plants need to keep a daily rhythm to synchronize their inner functions to the available energy and nutrients; even due to its sessile nature it’s especially important for a large group to find ways to reproduce by outcrossing. The endogenous clock regulates metabolic processes related to the synchronization of plant traits that allows its survival and successful reproduction in pollinator dependent plants. In this work, the circadian clock genes in Nicotiana attenuata were identified and found to have a conserved function, as demonstrated by yeast two-hybrid assays and a similar hypocotyl length phenotypes on transformed Arabidopsis thaliana plants using N. attenuata transferred genes. Under long day conditions (LD) NaLHY and NaTOC1 peak at dawn and dusk, respectively, without NaZTL having marked oscillations like other plant models. The silencing of circadian genes in N. attenuata using inverted repeat (ir) technique showed similar clock transcription profile alterations of NaCAB2 and hypocotyl growth alteration as in the established clock model. Yet, irTOC1 plants had a delayed elongation and flowering under LD unlike some other model plant accessions, but it is attributable to a different habitat and genetic background, as seen in cross latitudinal studies of other species. Floral traits under circadian control are relevant to synchronize the display and scent emission of N. attenuata with its night-pollinator Manduca sexta. Flower vertical movement temporally excludes other pollinators by reduced conspicuousness. The right synchronization improves outcrossing by M. sexta in the field since dysrhythmic floral traits decreased pollination rate. However, a lack of regulation caused basically arrhythmic floral traits since irZTL had unexpected advantages during day-time outcrossing in the field due to the recruitment of day-active pollinators that provided similar reproductive results as night-pollinator dependent plants.