Plants respond to the changing seasons to initiate developmental programmes precisely at particular times of year. Flowering is the best characterized of these seasonal responses, and in temperate climates it often occurs in spring. Genetic approaches in Arabidopsis thaliana have shown how the underlying responses to changes in day length (photoperiod) or winter temperature (vernalization) are conferred and how these converge to create a robust seasonal response. Recent advances in plant genome analysis have demonstrated the diversity in these regulatory systems in many plant species, including several crops and perennials, such as poplar trees. Here, we report progress in defining the diverse genetic mechanisms that enable plants to recognize winter, spring and autumn to initiate flower development.

The genetic basis of flowering responses to seasonal cues

Plants undergo a major physiological change as they transition from vegetative growth to reproductive development. This transition is a result of responses to various endogenous and exogenous signals that later integrate to result in flowering. Five genetically defined pathways have been identified that control flowering. The vernalization pathway refers to the acceleration of flowering on exposure to a long period of cold. The photoperiod pathway refers to regulation of flowering in response to day length and quality of light perceived. The gibberellin pathway refers to the requirement of gibberellic acid for normal flowering patterns. The autonomous pathway refers to endogenous regulators that are independent of the photoperiod and gibberellin pathways. Most recently, an endogenous pathway that adds plant age to the control of flowering time has been described. The molecular mechanisms of these pathways have been studied extensively in Arabidopsis thaliana and several other flowering plants.

http://files.estruturasreprodutivasplantasvas.webnode.com/200000008-2de802ee1d/floral%20meristem%202011.pdf

Regulation of flowering time: all roads lead to Rome

The coordination of the timing of flowering with seasonal and development cues is a critical life-history trait that has been shaped by evolution to maximize reproductive success. Decades of studying many plant species have revealed several of the fascinating systems that plants have evolved to control flowering time: such as the perception of day length in leaves, which leads to the production of a mobile signal, florigen, that promotes flowering at the shoot apical meristem; the vernalization process in which exposure to prolonged cold results in meristem competence to flower; and the juvenile to adult phase transition. Arabidopsis research has contributed greatly to understanding these systems at a molecular level.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-313X.2010.04148.x

Seasonal and developmental timing of flowering.

Cryptochromes are flavoprotein photoreceptors first identified in Arabidopsis thaliana, where they play key roles in growth and development. Subsequently identified in prokaryotes, archaea, and many eukaryotes, cryptochromes function in the animal circadian clock and are proposed as magnetoreceptors in migratory birds. Cryptochromes are closely structurally related to photolyases, evolutionarily ancient flavoproteins that catalyze light-dependent DNA repair. Here, we review the structural, photochemical, and molecular properties of cry-DASH, plant, and animal cryptochromes in relation to biological signaling mechanisms and uncover common features that may contribute to better understanding the function of cryptochromes in diverse systems including in man.

The Cryptochromes: Blue Light Photoreceptors in Plants and Animals

Cryptochromes (CRY) are photolyase-like blue-light receptors that mediate light responses in plants and animals. How plant cryptochromes act in response to blue light is not well understood. We report here the identification and characterization of the Arabidopsis CIB1 (cryptochrome-interacting basic-helix-loop-helix) protein. CIB1 interacts with CRY2 (cryptochrome 2) in a blue light-specific manner in yeast and Arabidopsis cells, and it acts together with additional CIB1-related proteins to promote CRY2-dependent floral initiation. CIB1 binds to G box (CACGTG) in vitro with a higher affinity than its interaction with other E-box elements (CANNTG). However, CIB1 stimulates FT messenger RNA expression, and it interacts with chromatin DNA of the FT gene that possesses various E-box elements except G box. We propose that the blue light-dependent interaction of cryptochrome(s) with CIB1 and CIB1-related proteins represents an early photoreceptor signaling mechanism in plants.

http://science.sciencemag.org/content/sci/322/5907/1535.full.pdf

Photoexcited CRY2 Interacts with CIB1 to Regulate Transcription and Floral Initiation in Arabidopsis

In Arabidopsis thaliana, the blue light photoreceptor cryptochromes (CRY) act to promote photomorphogenic development and the transition from vegetative to floral development in long days (LDs). We previously proposed that one of the mechanisms by which CRY regulates light responses is via its physical interaction with COP1, a RING motif-containing E3 ligase. Under LDs, the transcription of FLOWERING LOCUS T (FT) is activated by CONSTANS (CO) in leaf, and the FT protein moves to the shoot apex to induce flowering. CO protein is degraded in darkness, whereas it is stabilized by the CRY-mediated signal. However, the mechanism underlying this process is unknown. We show in this report that CO acts genetically downstream of COP1 and CRY to regulate flowering time. In addition, COP1 physically interacts with CO and functions as an E3 ligase, ubiquitinating CO in vitro and reducing CO levels in vivo. These results suggest that COP1 acts as a repressor of flowering by promoting the ubiquitin-mediated proteolysis of CO in darkness and that CRY-mediated signal may negatively regulate COP1, thereby stabilizing CO, activating FT transcription, and inducing flowering.

COP1-Mediated Ubiquitination of CONSTANS Is Implicated in Cryptochrome Regulation of Flowering in Arabidopsis

Autism Spectrum Disorder (ASD) is a series of complex neurodevelopmental disorders, which can affect children's social, behavioral and communication abilities. A member of the Sirtuins family of NAD + dependent deacetylases called SIRT2 could regulate the inflammation progress during stress, but the relevant mechanism has not been clearly defined. In the present study, the ASD model of wild type and SIRT2 knock out mice was established to evaluate the impact on the homeostasis of neurons in the hippocampus using western blotting, immunofluorescence and Nissl staining. The results showed that the amplification of neuronal richness was significantly decreased and neuroinflammation increased in the hippocampus following ASD due to autophagy, caused by enhancing the acetylation of FoxO1 using SIRT2 gene deletion and indicating this should be the target for ASD or other psychological stress treatment.

Neuro death through autophagy via the acetylation of FoxO1 by SIRT2 in the hippocampus of mice in a autism spectrum disorder mice model

Ginsenoside Rg1 Restores Sirt2/Foxo1 Expression and Alleviates Autism-Like Behaviors in a Valproic Acid Induced Male Mouse Model.

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COP1-Mediated Ubiquitination of CONSTANS Is Implicated in Cryptochrome Regulation of Flowering in Arabidopsis

Neuro death through autophagy via the acetylation of FoxO1 by SIRT2 in the hippocampus of mice in a autism spectrum disorder mice model

Ginsenoside Rg1 Restores Sirt2/Foxo1 Expression and Alleviates Autism-Like Behaviors in a Valproic Acid Induced Male Mouse Model.