Little is known about the capacity of Cannabis sativa to cold-acclimate and develop freezing tolerance. This study investigates the cold acclimation (CA) capacity of nine C. sativa varieties and the underlying genetic and epigenetic responses. The varieties were divided into three groups based on their contrasting CA capacities by comparing the survival of non-acclimated and cold-acclimated plants in whole-plant freeze tests. In response to the CA treatment, all varieties accumulated soluble sugars but only the varieties with superior capacity for CA could maintain higher levels throughout the treatment. In addition, the varieties that acclimated most efficiently accumulated higher transcript levels of cold-regulated (COR) genes and genes involved in de novo DNA methylation while displaying locus- and variety-specific changes in the levels of H3K9ac, H3K27me3 and methylcytosine (MeC) during CA. Furthermore, these hardy C. sativa varieties displayed significant increases in MeC levels at COR gene loci when deacclimated, suggesting a role for locus-specific DNA methylation in deacclimation. This study uncovers the molecular mechanisms underlying CA in C. sativa and reveals higher levels of complexity regarding how genetic, epigenetic and environmental factors intertwine.

To incorporate the far-red light (FR) signal into a strategy for optimizing plant growth, FAR-RED ELONGATED HYPOCOTYL1 (FHY1) mediates the nuclear translocation of the FR photoreceptor phytochrome A (phyA) and facilitates the association of phyA with the promoters of numerous associated genes crucial for the response to environmental stimuli. However, whether FHY1 plays additional roles after FR irradiation remains elusive. Here, through the global identification of FHY1 chromatin association sites through ChIP-seq analysis and by the comparison of FHY1-associated sites with phyA-associated sites, we demonstrated that nuclear FHY1 can either act independently of phyA or act in association with phyA to activate the expression of distinct target genes. We also determined that phyA can act independently of FHY1 in regulating phyA-specific target genes. Furthermore, we determined that the independent FHY1 nuclear pathway is involved in crucial aspects of plant development, as in the case of inhibited seed germination under FR during salt stress. Notably, the differential presence of cis-elements and transcription factors in common and unique FHY1-and/or phyA-associated genes are indicative of the complexity of the independent and coordinated FHY1 and phyA pathways. Our study uncovers previously unidentified aspects of FHY1 function beyond its currently recognized role in phyA-dependent photomorphogenesis.L ight is one of the most important environmental cues in plant growth and development. Arabidopsis has thus evolved several photoreceptors to perceive different wavelengths in the visible light spectrum (1). Among them, phytochrome A (phyA) is the primary photoreceptor to mediate the far-red light (FR) and early red light (R) responses (2, 3). PhyA therefore plays a predominant role in plant adaptation to a shade environment where the R/FR ratio decreases. Upon FR and R irradiation phyA will shuttle between the inactive R-absorbing Pr form and the active FR-absorbing Pfr form. These two forms display distinct biological activities, nuclear translocation rates, degradation rates, and affinities for various signaling intermediates (2, 4, 5).Both FR and R trigger the localization of cytosolic phyA to the nucleus (6), albeit through different mechanisms. Two essential partners for phyA nuclear translocation, FAR-RED ELONGATED HYPOCOTYL1 (FHY1) and its less abundant homolog FHY1-LIKE (FHL), influence this process at two levels; first, after the initial burst of phyA nuclear importation under R, FHY1 is gradually phosphorylated by action of the Pfr form of phyA (7). This event inhibits the nuclear translocation of FHY1 and consequently prevents further nuclear accumulation of phyA. Under FR, however, persistent phyA nuclear translocation is observed with nonphosphorylated FHY1 (8); second, the nucleo-cytoplasmic shuttling of FHY1/FHL is also reduced under R owing to the low dissociation rate of the Pfr-FHY1/ FHL complex. The FR-driven phyA conversion to its Pr form benefits the recycling of FHY1/FHL for continuous phyA n...

BackgroundThe interaction between viral oncoproteins such as Simian virus 40 TAg, adenovirus E1A, and human papilloma virus E7, and the retinoblastoma protein (pRB) occurs through a well characterized peptide sequence, LXCXE, on the viral protein and a well conserved groove in the pocket domain of pRB. Cellular proteins, such as histone deacetylases, also use this mechanism to interact with the retinoblastoma protein to repress transcription at cell cycle regulated genes. For these reasons this region of the pRB pocket domain is thought to play a critical role in growth suppression.ResultsIn this study, we identify and characterize a tumor derived allele of the retinoblastoma gene (RB1) that possesses a discrete defect in its ability to interact with LXCXE motif containing proteins that compromises proliferative control. To assess the frequency of similar mutations in the RB1 gene in human cancer, we screened blood and tumor samples for similar alleles. We screened almost 700 samples and did not detect additional mutations, indicating that this class of mutation is rare.ConclusionsOur work provides proof of principal that alleles encoding distinct, partial loss of function mutations in the retinoblastoma gene that specifically lose LXCXE dependent interactions, are found in human cancer.