BBX7 interacts with BBX8 to accelerate flowering in chrysanthemum

The quantitative control of FLOWERING LOCUS T(FT)activation is important for the floral transition in flowering plants.However,the flowering regulation mechanisms in the day-neutral,summer-flowering chrysanthemum plant remain unclear.In this study,the chrysanthemum BBX7 homolog CmBBX7 was isolated and its flowering function was identified.The expression of CmBBX7 showed a diurnal rhythm and CmBBX7 exhibited higher expression levels than CmBBX8.Overexpression of CmBBX7 in transgenic chrysanthemum accelerated flowering,whereas lines transfected with a chimeric repressor(pSRDX-CmBBX7)exhibited delayed flowering.Yeast single hybridization,luciferase,electrophoretic mobility shift,and chromatin immunoprecipitation assays showed that CmBBX7 directly targets CmFTL1.In addition,we found that CmBBX7 and CmBBX8 interact to positively regulate the expression of CmFTL1 through binding to its promoter.Collectively,these results highlight CmBBX7 as a key cooperator in the BBX8–FT module to control chrysanthemum flowering.

An early-morning gene network controlled by phytochromes and cryptochromes regulates photomorphogenesis pathways in Arabidopsis

Light perception at dawn plays a key role in coordinating multiple molecular processes and in entraining the plant circadian clock.The Arabidopsis mutant lacking the main photoreceptors,however,still shows clock entrainment,indicating that the integration of light into the morning transcriptome is not well understood.In this study,we performed a high-resolution RNA-sequencing time-series experiment,sampling every 2 min beginning at dawn.In parallel experiments,we perturbed temperature,the circadian clock,photoreceptor signaling,and chloroplast-derived light signaling.We used these data to infer a gene network that describes the gene expression dynamics after light stimulus in the morning,and then validated key edges.By sampling time points at high density,we are able to identify three light-and temperature-sensitive bursts of transcription factor activity,one of which lasts for only about 8 min.Phytochrome and cryptochrome mutants cause a delay in the transcriptional bursts at dawn,and completely remove a burst of expression in key photomorphogenesis genes(HY5 and BBX family).Our complete network is available online(http://www-users.york.ac.uk/∼de656/dawnBurst/dawnBurst.html).Taken together,our results show that phytochrome and cryptochrome signaling is required for fine-tuning the dawn transcriptional response to light,but separate pathways can robustly activate much of the program in their absence.