title: Genetic analysis of the roles of phytochromes A and B1 in the reversed gravitropic response of the lz-2 tomato mutant.
abstract: The lz-2 mutation in tomato (Lycopersicon esculentum) causes conditional reversal of shoot gravitropism by light. This response is mediated by phytochrome. To further elicit the mechanism by which phytochrome regulates the lz-2 phenotype, phytochrome-deficient lz-2 plants were generated. Introduction of au alleles, which severely block chromophore biosynthesis, eliminated the reversal of hypocotyl gravitropism in continuous red and far-red light. The fri1 and tri1 alleles were introduced to specifically deplete phytochromes A and B1, respectively. In dark-grown seedlings, phytochrome A was necessary for response to high-irradiance far-red light, a complete response to low fluence red light, and also mediated the effects of blue light in a far-red reversible manner. Loss of phytochrome B1 alone did not significantly affect the behaviour of lz-2 plants under any light treatment tested. However, dark-grown lz-2 plants lacking both phytochrome A and B1 exhibited reduced responses to continuous red and were less responsive to low fluence red light and high fluence blue light than plants that were deficient for phytochrome A alone. In high light, full spectrum greenhouse conditions, lz-2 plants grew downward regardless of the phytochrome deficiency. These results indicate that phytochromes A and B1 play significant roles in mediating the lz-2 phenotype and that at least one additional phytochrome is involved in reversing shoot gravitropism in this mutant.
authors.affiliation: Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331, USA.
authors.forename: F J
authors.initials: FJ
authors.lastname: Behringer
authors.forename: T L
authors.initials: TL
authors.lastname: Lomax
mesh_terms: D000483:Alleles; D003624:Darkness; D017343:Genes, Plant; D018522:Gravitropism / Q000235:genetics* / Q000502:physiology / Q000528:radiation effects*; D018466:Gravity Sensing; D018546:Hypocotyl / Q000235:genetics / Q000254:growth & development / Q000528:radiation effects; D008027:Light; D018551:Solanum lycopersicum / Q000235:genetics / Q000254:growth & development / Q000528:radiation effects*; D009154:Mutation; D010641:Phenotype; D010786:Photoreceptor Cells; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics / Q000528:radiation effects; D010834:Phytochrome / Q000235:genetics* / Q000502:physiology* / Q000528:radiation effects; D051942:Phytochrome A; D051939:Phytochrome B; D014157:Transcription Factors
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins; D051942:Phytochrome A; D014157:Transcription Factors; D010834:Phytochrome; D051939:Phytochrome B