Phytochrome A Overexpression in Transgenic Tobacco (Correlation of Dwarf Phenotype with High Concentrations of Phytochrome in Vascular Tissue and Attenuated Gibberellin Levels)

Abstract

Phytochromes are a family of related chromoproteins that regulate photomorphogenesis in plants. Ectopic overexpression of the phytochrome A in severa1 plant species has pleiotropic effects, including substantial dwarfing, increased pigmentation, and delayed leaf senescence. We show here that the dwarf response is related to a reduction in active gibberellins (CAs) in tobacco (Nicofiana fabacum) overexpressing oat phytochrome A under the control of the cauliflower mosaic virus (CaMV) 35s promoter and can be suppressed by foliar applications of gibberellic acid. In transgenic seedlings, high concentrations of oat phytochrome A were detected in stem and petiole vascular tissue (consistent with the activity of the CaMV 35s promoter), implicating vascular tissue as a potential site of phytochrome A action. To examine the efficacy of this cellular site, oat phytochrome A was also expressed using Arabidopsis chlorophyll a/b-binding protein (CAB) and the Arabidopsis ubiquitin (UBQ7) promoters. Neither promoter was as effective as CaMV 35s in expressing phytochrome in vascular tissue or in inducing the dwarf phenotype. Collectively, these data indicate that the spatial distribution of ectopic phytochrome i s important in eliciting the dwarf response and suggest that the phenotype is invoked by elevated levels of the far-red-absorbing form of phytochrome within vascular tissue repressing CA biosynthesis.Phytochromes are a family of regulatory photoreceptors in plants that measure both the quantity and quality of available light (for reviews, see Quail, 1991;Vierstra, 1993;Kendrick and Kronenberg, 1994). They are dimeric, cytoplasmic proteins, with each subunit consisting of a linear tetrapyrrole chromophore covalently linked to an approx-

Flowers into shoots: Photo and hormonal control of a meristem identity switch in Arabidopsis

“…First, previous studies showed that gibberellin synthesis or activity is governed by photoperiod in many plant species including Arabidopsis (38-41). In tobacco, gibberellin levels in the leaf can be reduced by the overexpression of the oat phytochrome A gene (42). Second, the gibberellins are one of at least two signals that can promote flowering in Arabidopsis (6)(7)(8).…”

Physiological regulation and functional significance of shade avoidance responses to neighbors

“…A study with tobacco also overexpressing oat PHYA, confirmed the strong inhibition of the SAS, 57 including inhibition of internode and petiole elongation, but also showed that the SAS could be restored by external GA application. 58 In A. thaliana, low R:FR promotes the expression of GA-related genes 59 and the constitutively elongated phenotype of phyB mutants is suppressed by GA deficiency and GA insensitivity. 60 A direct link between GA and the SAS has been shown for A. thaliana, since low R:FR treatment appears to enhance both GA biosynthesis 61 and responsiveness.…”

Phytochrome Phosphorylation Modulates Light Signaling by Influencing the Protein–Protein Interaction[W]

“…To assess the expression of oat phyA and S598A mutant proteins in adult plants, protein gel blot analysis was performed as described (Jordan et al, 1995): four leaves were removed before bolting, the leaves were incubated between soaked Whatman papers for at least 12 h in the dark condition, leaf tissues were ground with sea sand, and 50 mg of protein samples were loaded onto 10% SDS-PAGE gels for electrophoresis (Laemmli, 1970). The protein bands on the SDS-PAGE gel were transferred to a polyvinylidene difluoride membrane (Hybond-P; Amersham Pharmacia Biotech), and the membrane was incubated with oat phyA-specific monoclonal antibody, oat22 or oat25 (Cordonnier et al, 1983), for 2 h and developed using an ECL protein gel blotting analysis system (Amersham Pharmacia Biotech).…”

“…Seedlings were then illuminated with red light (10 mmol/m 2 /s) and harvested at time intervals (0, 6, 12, and 24 h) for 24 h. The harvested seedlings were stored in liquid nitrogen, and the protein samples were prepared as described (Jordan et al, 1995). Five micrograms of crude extracts were loaded onto SDS-PAGE gels, and protein gel blot analysis was performed to detect phytochromes.…”