Extension-growth responses and expression of flavonoid biosynthesis genes in the Arabidopsis hy4 mutant

Abstract

The hy4 mutant of Arabidopsis thaliana (L.) Heynh. was previously shown to be impaired in the suppression of hypocotyl extension specifically by blue light. We report here that hy4 is altered in a range of blue-light-mediated extension-growth responses in various organs in seedlings and mature plants: it shows greater length of bolted stems, increased petiole extension and increased leaf width and area in blue light compared to the wild type. The hy4 mutant shows decreased cotyledon expansion in both red and blue light compared to the wild type. Anthocyanin formation and the expression of several flavonoid biosynthesis genes is stimulated by blue light in the wild type but to a much lower extent in hy4. The results indicate that the HY4 gene product is concerned with the perception of blue light in a range of extension-growth and gene-expression responses in Arabidopsis.

Separate functions for nuclear and cytoplasmic cryptochrome 1 during photomorphogenesis ofArabidopsisseedlings

“…Blue light promotes cotyledon expansion by cry1 signaling (3,4). The effect is evidenced here by the reduced cotyledon area of cry1 seedlings grown in blue light, especially at higher fluence rates (Fig.…”

“…Through signaling pathways that are being intensively studied, these photoreceptors convert the quality, quantity, and direction of incident light into developmental and physiological responses that best adapt the plant to the prevailing light environment. The cryptochrome photoreceptors of plants absorb UV-A/blue wavelengths (1) and mediate the suppression of seedling stem growth (2), promotion of leaf and cotyledon expansion (3,4), flowering time (5,6), resetting of the circadian oscillator (7), chlorophyll and anthocyanin synthesis (8), programmed cell death (9), and other processes. Widespread in biology, cryptochromes are known to regulate circadian rhythms in many organisms, including mammals (10).…”

The cryptochrome family of photoreceptors

“…These observations add to the earlier conclusions in demonstrating that under certain conditions phytochrome responses may be dependent on a functional cryptochrome. Not all cryptochrome responses require phytochrome, as chaicone synthase expression which, although mediated by CRYl Jackson & Jenkins 1995), is still observed in the phyA phyB double mutant (Batschauer et al 1996), differing in this respect from anthocyanin production.…”

The signal transducing photoreceptors of plants

“…Originally designated hy4, an Arabidopsis mutant deficient in cry1 was isolated based on its long hypocotyl phenotype in blue light with no differences from wild type seedlings observed in R or FR (Koornneef et al, 1980., Ahmad et al, 1995, Lin et al, 1996. In addition to elongated hypocotyls, cry1-deficient seedlings also displayed smaller cotyledons and reduced anthocyanin levels in blue light when compared with wild types (Ahmad et al, 1995, Jackson andJenkins, 1995). Reductions in anthocyanin content were accompanied by decreases in the blue light-induced transcription of genes encoding enzymes early in the phenylpropanoid pathway, such as chalcone synthase (Ahmad et al, 1995, Jackson andJenkins, 1995).…”

“…In addition to elongated hypocotyls, cry1-deficient seedlings also displayed smaller cotyledons and reduced anthocyanin levels in blue light when compared with wild types (Ahmad et al, 1995, Jackson andJenkins, 1995). Reductions in anthocyanin content were accompanied by decreases in the blue light-induced transcription of genes encoding enzymes early in the phenylpropanoid pathway, such as chalcone synthase (Ahmad et al, 1995, Jackson andJenkins, 1995). The isolation of an Arabidopsis mutant deficient in cry2 and the construction of CRY2 -overexpressing plants revealed roles for this photoreceptor in blue light signalling.…”