Physiological interactions of phytochromes A, B1 and B2 in the control of development in tomato

Abstract

SummaryThe role of phytochrome B2 (phyB2) in the control of photomorphogenesis in tomato (Solanum lycopersicum L.) has been investigated using recently isolated mutants carrying lesions in the PHYB2 gene. The physiological interactions of phytochrome A (phyA), phytochrome B1 (phyB1) and phyB2 have also been explored, using an isogenic series of all possible mutant combinations and several different phenotypic characteristics. The loss of phyB2 had a negligible effect on the development of white-lightgrown wild-type or phyA-de®cient plants, but substantially enhanced the elongated pale phenotype of the phyB1 mutant. This redundancy was also seen in the control of de-etiolation under continuous red light (R), where the loss of phyB2 had no detectable effect in the presence of phyB1. Under continuous R, phyA action was largely independent of phyB1 and phyB2 in terms of the control of hypocotyl elongation, but antagonized the effects of phyB1 in the control of anthocyanin synthesis, indicating that photoreceptors may interact differently to control different traits. Irradiance response curves for anthocyanin synthesis revealed that phyB1 and phyB2 together mediate all the detectable response to high-irradiance R, and, surprisingly, that the phyA-dependent low-irradiance component is also strongly reduced in the phyB1 phyB2 double mutant. This is not associated with a reduction in phyA protein content or responsiveness to continuous far-red light (FR), suggesting that phyB1 and phyB2 speci®cally in¯uence phyA activity under low-irradiance R. Finally, the phyA phyB1 phyB2 triple mutant showed strong residual responsiveness to supplementary daytime FR, indicating that at least one of the two remaining phytochromes plays a signi®cant role in tomato photomorphogenesis.

Remote sensing of future competitors: Impacts on plant defenses

“…The effects of these factors were tested independently (insect bioassays and gene expression) or in factorial combination (leaf chemistry). Seeds of the phyB1-phyB2 double mutant (22) of tomato (Lycopersicon esculentum L.) and its corresponding wild type (Money Maker cv.) were germinated on moist paper; 7 days later, the seedlings were transferred to 1.5-liter pots.…”

“…Genetic approaches are not possible with N. longiflora, but functional questions can be addressed by using tomato as a taxonomically related model organism. We used the phyB1-phyB2 double mutant of tomato (22), which lacks functional phytochrome B and has the phenotype of a FR-exposed plant even when grown in full sunlight (Fig. 4A).…”

Evolutionary Studies Illuminate the Structural-Functional Model of Plant Phytochromes

“…each photoreceptor, although few data are available to test the conservation of gene function in seed plants other than Arabidopsis. Nonetheless, the available data from Brassica, cucumber (Cucumis sativus), pea (Pisum sativum), tobacco (Nicotiana tabacum), tomato (Solanum lycopersicum), maize (Zea mays), and rice (Oryza sativa) suggest that the functions of phyA and phyB are generally conserved and were established prior to the split of eudicots and monocots (Ballaré et al, 1991;Childs et al, 1991;Devlin et al, 1992;Weller et al, 2004;Sheehan et al, 2007;Takano et al, 2005Takano et al, , 2009, although independently duplicated phyB may subdivide functions differently than is seen in Arabidopsis phyB and phyD (e.g., Hudson et al, 1997;Kerckhoffs et al, 1999;Weller et al, 2000;Sheehan et al, 2007). Functional data from dicots that diverge deeper than the eudicot/monocot split in the angiosperm phylogenetic tree are needed to infer that their functions are conserved in all angiosperms, but this is a reasonable hypothesis.…”

Phytochromes are the sole photoreceptors for perceiving red/far-red light in rice

“…To date, quadruple mutants (phyAphyBphyDphyE and phyBphyCphyDphyE) have been produced and analyzed (14,15), but the quintuple mutant remains to be studied. The tomato also has five phytochrome genes (PHYA, PHYB1, PHYB2, PHYE, and PHYF) and a triple mutant (phyAphyB1phyB2) is the most that has been reported (16). In contrast, rice only has three phytochrome genes, which makes it simpler to produce the phytochrome null mutant (that is, the triple mutant).…”