RESUMO
Plants are extremely sensitive to changes in their environment, particularly variations in photoperiod or day length. Photoperiodism refers to a plant's capacity to detect variations in day length and make use of this knowledge to control key developmental processes including flowering, growth, and dormancy. Through a process known as photoperiodism, plants can detect and react to variations in the number of daylight hours, or photoperiod. The physiological response of plants to the length of day or night is known as photoperiodism. The plant uses this physiological response to time-critical developmental events like flowering. In this essay, I will cover the current understanding of how plants respond to photoperiod and the molecular mechanisms underpinning this response. Three groups of plants' photoperiodic responses can be distinguished: short-day plants (SDPs), long-day plants (LDPs), and day-neutral plants (DNPs). Whereas LDPs bloom when the length of the day exceeds the crucial threshold, SDPs do so only when it is shorter than the critical threshold. Conversely, DNPs do not have a crucial day duration and can bloom at any day length. Many genes and biochemical processes control how a plant responds to the photoperiod. The creation and movement of the hormone florigen, which starts blooming in response to photoperiodic signals, is a crucial regulating mechanism. On the other hand, a class of photoreceptors known as phytochromes is involved in the biochemical mechanisms driving photoperiodic responses in plants. The perception of light's duration, quality, and amount is caused by phytochromes. The red-light-absorbing Pr form and the far-red-light-absorbing Pfr form are the two interconvertible states in which they can exist. The ratio of Pr to Pfr is altered by the duration of light exposure and is utilizes by plants to assess day length. Exposure to light in SDPs causes the expression of the CONSTANS (CO) gene, and the CO protein causes the expression of the FLOWERING LOCUS T (FT), a gene that encourages flowering. By exposing LDPs to light, a different gene called GI (GIGANTEA) is induced rather than CO, which is normally expressed. The FT gene's expression is encouraged by GI's interaction with the protein ZEITLUPE (ZTL), which also encourages flowering. In addition to these essential elements, several proteins and signalling pathways are also involved in photoperiodic responses in plants. For instance, to optimise the response to variations in day length, the photoperiodic pathway interacts with the circadian clock, which controls numerous physiological processes in plants. In some species, the hormone gibberellin (GA) also aids in the promotion of flowering. One essential adaptation that enables plants to synchronize their developmental processes with seasonal changes is their capacity to react to variations in day length. Phytochromes play a key role in how plants perceive the day in the complex network of proteins and signalling channels that make up the molecular mechanisms behind photoperiodic responses in plants. There is still much to learn about the diversity and complexity of the photoperiodic response across several plant groupings, even if much is known about it in particular species.
RESUMO
Objective:To investigate changes in circadian gene cryptochrome 2 (CRY2) expression in mouse models of psoriasis and HaCaT cells, and to explore underlying mechanisms.Methods:Imiquimod-induced mouse model experiment: 12 C57BL/6 female mice were randomly and equally divided into imiquimod group receiving topical imiquimod treatment for 5 consecutive days and control group receiving no treatment; these mice were sacrificed on day 6, skin tissues were resected from the back of mice, and immunofluorescence staining was performed to determine the CRY2 expression in the epidermis. HaCaT cell transfection experiment: HaCaT cells with small interfering RNA (siRNA) -mediated knockdown of CRY2 served as siRNA-CRY2 group, and siRNA-NC group as control group; 5-ethynyl-2′-deoxyuridine (EdU) staining was performed to evaluate the proliferative activity of the HaCaT cells, real-time fluorescence-based quantitative PCR (qPCR) to determine the mRNA expression of chemokines in the HaCaT cells, and Western blot analysis to determine phosphorylation levels of extracellular signal-regulated kinase 1/2 (ERK1/2) . Tumor necrosis factor-α (TNF-α) -stimulated animal and cell experiments: 12 C57BL/6 female mice were randomly and equally divided into TNF-α group subcutaneously injected with TNF-α solution in the ear for 6 days, and phosphate buffered saline (PBS) group subcutaneously injected with the same amount of PBS; the mice were sacrificed on day 7, skin tissues were resected from the ear of mice, and immunofluorescence staining was conducted to determine the CRY2 expression in the epidermis; CRY2-knockdown HaCaT cells stimulated with 50 ng/ml TNF-α for 12 hours served as siRNA-CRY2 + TNF-α group, and siRNA-NC + TNF-α group as control group; qPCR was performed to determine the mRNA expression of chemokines in HaCaT cells in the above groups. Statistical analysis was carried out by using two-independent-sample t test. Results:Immunofluorescence staining showed that the CRY2 protein expression was significantly lower in the mouse dorsal epidermis in the imiquimod group (0.94 ± 0.23) than in the control group (2.30 ± 0.25, t = 3.99, P = 0.016) . Compared with the siRNA-NC group, the siRNA-CRY2 group showed significantly increased proportions of EdU-positive cells (48.13% ± 10.97% vs. 38.23% ± 0.81%, t = 5.00, P = 0.007) , mRNA expression levels of chemokines CXCL1 and CXCL8, as well as significantly increased phosphorylated (p) -ERK1/2 protein expression levels (all P < 0.05) , while there were no significant differences in the CCL20 mRNA expression or ERK1/2 protein expression between the two groups (both P > 0.05) . Immunofluorescence staining showed significantly decreased CRY2 protein expression level in the mouse ear epidermis in the TNF-α group (0.37 ± 0.34) compared with the PBS group (2.04 ± 0.17, t = 4.38, P = 0.012) ; the relative mRNA expression levels of chemokines CXCL1, CXCL8, and CCL20 in HaCaT cells were significantly higher in the siRNA-CRY2 + TNF-α group than in the siRNA-NC + TNF-α group (all P < 0.05) . Conclusion:CRY2 was markedly underexpressed in psoriasis, which might promote the proliferation of keratinocytes and expression of chemokines CXCL1, CXCL8 and CCL20, and TNF-α might be an upstream cytokine that could downregulate CRY2 expression.