ABSTRACT
The Arabidopsis UV-B photoreceptor UV RESISTANCE LOCUS 8 (UVR8) orchestrates the expression of hundreds of genes, many of which can be associated with UV-B tolerance. UV-B does not efficiently penetrate into tissues, yet UV-B regulates complex growth and developmental responses. To unravel to what extent and how UVR8 located in different tissues contributes to UV-B-induced responses, we expressed UVR8 fused to the YELLOW FLUORESCENT PROTEIN (YFP) under the control of tissue-specific promoters in a uvr8 null mutant background. We show that (1) UVR8 localized in the epidermis plays a major role in regulating cotyledon expansion, and (2) expression of UVR8 in the mesophyll is important to protect adult plants from the damaging effects of UV-B. We found that UV-B induces transcription of selected genes, including the key transcriptional regulator ELONGATED HYPOCOTYL 5 (HY5), only in tissues that express UVR8. Thus, we suggest that tissue-autonomous and simultaneous UVR8 signalling in different tissues mediates, at least partly, developmental and defence responses to UV-B.
Subject(s)
Arabidopsis Proteins/metabolism , Arabidopsis/radiation effects , Chromosomal Proteins, Non-Histone/metabolism , Acclimatization , Arabidopsis/genetics , Arabidopsis/metabolism , Arabidopsis Proteins/genetics , Bacterial Proteins/genetics , Bacterial Proteins/metabolism , Basic-Leucine Zipper Transcription Factors/genetics , Basic-Leucine Zipper Transcription Factors/metabolism , Chromosomal Proteins, Non-Histone/genetics , Flavonoids/metabolism , Gene Expression Regulation, Plant , Hypocotyl/growth & development , Hypocotyl/metabolism , Luminescent Proteins/genetics , Luminescent Proteins/metabolism , Mesophyll Cells/metabolism , Mutation , Nuclear Proteins/genetics , Nuclear Proteins/metabolism , Photoreceptors, Plant/genetics , Photoreceptors, Plant/metabolism , Plants, Genetically Modified , Promoter Regions, Genetic , Seedlings/genetics , Seedlings/metabolism , Signal Transduction , Ultraviolet RaysABSTRACT
The precise adjustment of the timing of dormancy release according to final grain usage is still a challenge for many cereal crops. Grain sorghum [Sorghum bicolor (L.) Moench] shows wide intraspecific variability in dormancy level and susceptibility to pre-harvest sprouting (PHS). Both embryo sensitivity to abscisic acid (ABA) and gibberellin (GA) metabolism play an important role in the expression of dormancy of the developing sorghum grain. In previous works, it was shown that, simultaneously with a greater embryo sensitivity to ABA and higher expression of SbABA-INSENSITIVE 4 (SbABI4) and SbABA-INSENSITIVE 5 (SbABI5), dormant grains accumulate less active GA4 due to a more active GA catabolism. In this work, it is demonstrated that the ABA signalling components SbABI4 and SbABI5 interact in vitro with a fragment of the SbGA 2-OXIDASE 3 (SbGA2ox3) promoter containing an ABA-responsive complex (ABRC). Both transcription factors were able to bind the promoter, although not simultaneously, suggesting that they might compete for the same cis-acting regulatory sequences. A biological role for these interactions in the expression of dormancy of sorghum grains is proposed: either SbABI4 and/or SbABI5 activate transcription of the SbGA2ox3 gene in vivo and promote SbGA2ox3 protein accumulation; this would result in active degradation of GA4, thus preventing germination of dormant grains. A comparative analysis of the 5'-regulatory region of GA2oxs from both monocots and dicots is also presented; conservation of the ABRC in closely related GA2oxs from Brachypodium distachyon and rice suggest that these species might share the same regulatory mechanism as proposed for grain sorghum.
Subject(s)
Plant Dormancy , Plant Proteins/metabolism , Promoter Regions, Genetic , Sorghum/genetics , Transcription Factors/metabolism , Base Sequence , Computer Simulation , Conserved Sequence , Gene Expression Regulation, Plant , Molecular Sequence Data , Phylogeny , Plant Proteins/genetics , Sorghum/metabolism , Transcription Factors/geneticsABSTRACT
Tomato (Solanum lycopersicum) seed germination can be inhibited by continuous irradiation with far-red light (FRc) and re-induced by a subsequent red light pulse. In this study, we carried out a global transcript analysis of seeds subjected to FRc inhibitory treatment, with and without a subsequent red light pulse, using potato cDNA microarrays. We also identified and characterized genes involved in light-modulated germination as elements of the phytochrome signalling pathway. Microarray data showed that the inhibition of germination by FRc involves the induction of a large number of genes and the repression of a significantly smaller quantity. Multivariate analysis established an underlying pattern of expression dependent on physiological treatment and incubation time, and identified different groups of genes associated with dormancy maintenance, inhibition and promotion of germination. We showed that ELIP, CSN6, SOS2 and RBP are related to the photocontrol of germination. These genes are known to participate in other physiological processes, but their participation in germination has not been suggested previously. Light quality regulates the tomato seed transcriptome during phytochrome-modulated germination through changes in the expression of certain sets of genes. In addition, ELIP and GIGANTEA were confirmed as components of the phytochrome A signalling pathway during FRc inhibition of germination.