UV and blue light stimulate transcription of key flavonoid biosynthesis genes in a range of higher plants. Here, we provide evidence that several distinct "inductive" and "synergistic" UV/blue phototransduction pathways regulate chalcone synthase (CHS) gene transcription and transcript accumulation in Arabidopsis leaf tissue. Experiments with the long-hypocotyl hy4-2.23N mutant showed that separate inductive pathways mediate responses to UV-B and UV-A/blue light. Only the UV-A/blue light induction of CHS expression involved the CRY1 photoreceptor. In addition, UV-A and blue light each act synergistically with UV-B to stimulate CHS transcript accumulation and beta-glucuronidase activity driven by a CHS promoter in transgenic leaf tissue. The UV-A and blue phototransduction pathways responsible for synergism are distinct because they produce transient and relatively stable signals, respectively, and can function additively to stimulate CHS promoter function. The hy4-2.23N mutant retains the synergistic interactions between UV-B and both UV-A and blue light, indicating that neither synergism pathway involves the CRY1 photoreceptor. Our findings reveal considerable complexity in both photoreception and signal transduction in regulating CHS gene expression by UV and blue light.

UV and blue light stimulate transcription of key flavonoid biosynthesis genes in a range of higher plants. Here, we provide evidence that several distinct "inductive" and "synergistic" UV/blue phototransduction pathways regulate chalcone synthase (CHS) gene transcription and transcript accumulation in Arabidopsis leaf tissue. Experiments with the long-hypocotyl hy4-2.23N mutant showed that separate inductive pathways mediate responses to UV-B and UV-A/blue light. Only the UV-A/blue light induction of CHS expression involved the CRY1 photoreceptor. In addition, UV-A and blue light each act synergistically with UV-B to stimulate CHS transcript accumulation and beta-glucuronidase activity driven by a CHS promoter in transgenic leaf tissue. The UV-A and blue phototransduction pathways responsible for synergism are distinct because they produce transient and relatively stable signals, respectively, and can function additively to stimulate CHS promoter function. The hy4-2.23N mutant retains the synergistic interactions between UV-B and both UV-A and blue light, indicating that neither synergism pathway involves the CRY1 photoreceptor. Our findings reveal considerable complexity in both photoreception and signal transduction in regulating CHS gene expression by UV and blue light.

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Transgenic Arabidopsis expressing beta-glucuronidase (GUS) driven by a chalcone synthase gene (CHS) promoter were produced. GUS activity in the leaves increased with increasing fluence rates of white light in parallel with endogenous CHS transcript levels. An isogenic line homozygous for the transgene was obtained and mutagenized seedlings of this line were screened for altered light-induction of the transgene. Putative mutants with low GUS activity were not altered in the light-induction of endogenous CHS transcripts and are therefore not regulatory mutants. Two mutant lines (A12 and C10) with elevated levels of GUS activity in the light show a corresponding increase in CHS transcript levels. The A12 mutant was focussed upon and designated icx1 (increased chalcone synthase expression). This mutant has enhanced light-stimulation of CHS expression since CHS transcript levels in darkness in icx1 are very low, as in the wild-type. The transcript levels of two other genes involved in flavonoid biosynthesis are elevated in the light in icx1 as is anthocyanin formation. However, there is no alteration in LHCII chlorophyll a/b-binding protein gene (CAB) transcript levels under the same conditions. The altered gene expression phenotype of icx1 co-segregates with several other phenotypic characteristics, including fewer leaf trichomes and alterations to the seed coat. On the basis of these data and comparison with the Arabidopsis ttg (transparent testa glabra) mutant, it is suggested that the ICX1 gene product may be concerned both with the light-regulation of gene expression and with developmental processes occurring in the epidermis.

Coprecipitation leads to self-assembly of bioactive DNA on the surface of salt, sugar or amino-acid crystals and provides a rapid inexpensive immobilization method suitable for preparing dry-powder formulations of nucleic acids, useful for storage, imaging and drug delivery.