Genetic dissection of blue-light sensing in tomato using mutants deficientin cryptochrome 1 and phytochromes A, B1 and B2

Several novel allelic groups of tomato (Solanum lycopersicum L.) mutants wi th impaired photomorphogenesis have been identified after gamma -ray mutage nesis of phyA phyB1 double-mutant seed. Recessive mutants in one allelic gr oup are characterized by retarded hook opening, increased hypocotyl elongat ion and reduced hypocotyl chlorophyll content under white light (WL). These mutants showed a specific impairment in response to blue light (BL) result ing from lesions in the gene encoding the BL receptor cryptochrome 1 (cry1) . Phytochrome A and cry1 are identified as the major photoreceptors mediati ng BL-induced de-etiolation in tomato, and act under low and high irradianc es, respectively. Phytochromes B1 and B2 also contribute to BL sensing, and the relative contribution of each of these four photoreceptors differs acc ording to the light conditions and the specific process examined. Developme nt of the phyA phyB1 phyB2 cry1 quadruple mutant under WL is severely impai red, and seedlings die before flowering. The quadruple mutant is essentiall y blind to BL, but experiments employing simultaneous irradiation with BL a nd red light suggest that an additional non-phytochrome photoreceptor may b e active under short daily BL exposures. In addition to effects on de-etiol ation, cry1 is active in older, WL-grown plants, and influences stem elonga tion, apical dominance, and the chlorophyll content of leaves and fruit. Th ese results provide the first mutant-based characterization of cry1 in a pl ant species other than Arabidopsis.