Cryptochrome 1 (CRY1) is a blue light receptor that mediates primarily blue-light inhibition of hypocotyl elongation. Very little is known of the mechanisms by which CRY1 affects growth. Blue light and temperature are two key environmental signals that profoundly affect plant growth and development, but how these two abiotic factors integrate remains largely unknown. Here, we show that blue light represses high temperature-mediated hypocotyl elongation via CRY1. Furthermore, CRY1 interacts directly with PHYTOCHROME-INTERACTING FACTOR 4 (PIF4) in a blue lightdependent manner to repress the transcription activity of PIF4. CRY1 represses auxin biosynthesis in response to elevated temperature through PIF4. Our results indicate that CRY1 signal by modulating PIF4 activity, and that multiple plant photoreceptors [CRY1 and PHYTOCHROME B (PHYB)] and ambient temperature can mediate morphological responses through the same signaling component-PIF4.ryptochromes are photolyase-like blue-light receptors first discovered in Arabidopsis and later found in all major evolutionary lineages (1-4). Arabidopsis cryptochrome 1 (CRY1) and cryptochrome 2 (CRY2) mediate primarily blue-light inhibition of hypocotyl elongation (5) and photoperiodic control of floral initiation (6) via modulation of gene expression. For example, Arabidopsis CRY2 undergoes blue light-dependent interaction with CIB1 (CRY2 Interacting bHLH1) to regulate flowering time (7-9). CRYs also suppress the E3 ubiquitin ligase activity of COP1 (CONSTITUTIVE PHOTOMORPHOGENIC 1) by forming a complex with SPA1 (SUPPRESSOR OF PHYA-105) and COP1 in a blue light-dependent manner (10-13). COP1 is a RING finger E3 ubiquitin ligase that acts downstream of phytochromes, cryptochromes, and UVR8 (UV Resistance Locus 8) (14,15) and is responsible for the degradation of various transcription factors in the dark, such as the bHLH transcription factor HFR1 (LONG HYPOCOTYL IN FAR RED1) and the bZIP factor HY5 (12,(16)(17)(18). Whether Arabidopsis CRY1 undergoes blue light-dependent interaction with transcription factors to regulate hypocotyl elongation is still unknown.In addition to light, ambient temperature serves as another key environmental cue that affects plant growth and development, but does not induce stress responses to any significant degree (19). Temperature regulates gene expression via chromatin remodeling and also regulation of transcription. It has been demonstrated that H2A.Z histone variant-containing nucleosomes act as thermosensors and mediate temperature induced transcriptome changes (20). PHYTOCHROME-INTERACTING FACTOR 4 (PIF4) is a bHLH transcription factor directly link red light photoreceptor PHYTOCHROME B (PHYB) to light-regulated gene expression and plant development (21-23). PIF4 also plays a role in sensing high temperature, it not only regulates temperature-mediated floral induction in the short day condition through direct activation of FT (FLOWERING LOCUS T) (24), but it also controls high temperature-induced hypocotyl elongation by increasing free indo...

Many different functions are regulated by circadian rhythms, including those orchestrated by discrete clock neurons within animal brains. To comprehensively characterize and assign cell identity to the 75 pairs of Drosophila circadian neurons, we optimized a single-cell RNA sequencing method and assayed clock neuron gene expression at different times of day. The data identify at least 17 clock neuron categories with striking spatial regulation of gene expression. Transcription factor regulation is prominent and likely contributes to the robust circadian oscillation of many transcripts, including those that encode cell-surface proteins previously shown to be important for cell recognition and synapse formation during development. The many other clock-regulated genes also constitute an important resource for future mechanistic and functional studies between clock neurons and/or for temporal signaling to circuits elsewhere in the fly brain.