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. 2014 Sep 16;5:474. doi: 10.3389/fpls.2014.00474

FIGURE 1.

FIGURE 1

Simplified model showing the UV radiation signaling pathways in plants and their possible links to an epigenetic based memory. (A) The MAP kinase MPK3 and MPK6 signaling pathway can be activated by UV stress whereas MKP1 suppresses the activation. (B) UVR8 signaling pathway, the dimerization of the UV photoreceptor UVR8 with COP1 upregulates the expression of UV targets genes including HY5 and HYH which activate further UV response genes. In turn, the expression of RUP1 and RUP2 establish a negative feedback loop by direct protein binding. (C) HY5 can upregulate the expression of enzymes involved in flavonoid and anthocyanin biosynthesis. (D) Change of antagonistic epigenetic marks to light and UV stress could be part of an epigenetic memory but it remains unclear whether the activation of the MKP1/MPK3/MPK6 (A) or the UVR8 signaling pathway (B) by UV can establish persistent chromatin modifications. The phytohormone SA (E) can prime response genes by setting H3K4me3 at their loci that increase the transcriptional response (B) by a second stress. (E) UV-B promotes the accumulation of ROS that induces the production of phytohormones including SA, JA, and Et. High ROS concentration cause senescence and cell death. (F) UV radiation can cause cyclobutane pyrimidine dimers and DNA double strand breaks that can trigger cell death (E). DNA damage repair pathways involve chromatin modifications including histone acetylation and remodeling to correct UV induced DNA lesions. There is a potential link between DNA repairs (F) and epigenetic memory (D). CHI, CHALCONE ISOMERASE; CHS, CHALCONE SYNTHASE;; COP1, CONSTITUTIVELY PHOTOMORPHOGENIC 1; DFR, DIHYDROFLAVONOL 4-REDUCTASE; Et., ethylene; F3H, FLAVANONE 3-HYDROXYLASE; F3′H, FLAVONOID 3′-HYDROXYLASE; FLS, FLAVONOL SYNTHASE; HY5, ELONGATED HYPOCOTYL 5; HYH, HY5 HOMOLOG; JA, jasmonate; LDOX, LEUCOANTHOCYANIDIN DIOXYGENASE; MKP1, MAP KINASE PHOSPHATASE 1; MPK3 and MPK6, MITOGEN-ACTIVATED PROTEIN KINASES 3 and 6, ROS, reactive oxygen species; RUP1 and RUP2, REPRESSOR OF UV-B PHOTOMORPHOGENESIS 1 and 2; SA, salicylic acid; UV, ultraviolet radiation; UVR8, UV RESISTANCE LOCUS 8.