The rice phytochrome gene: structure, autoregulated expression, and binding of GT-1 to a conserved site in the 5' upstream region.
We have isolated and characterized both cDNA and genomic clones encoding the apoprotein of rice phytochrome. The mRNA produced from this gene is expressed at a low level in etiolated leaves. Following a flash of red light, the steady-state mRNA level decreases within 15 minutes, and is barely detectable after 2 hours. This effect is partially reversed by far red light demonstrating autoregulation of phytochrome mRNA levels. Nuclear run-on experiments show that this effect is exerted on transcription of the phytochrome gene. In etiolated plants, phytochrome mRNA is twofold higher in leaves than in roots, whereas the reverse is true in fully green plants where phytochrome mRNA accumulates despite illumination of the leaves. DNA gel blots and screening of libraries indicate the presence of only a single gene, allowing convenient study of the autoregulatory phenomenon for a specific phytochrome gene. Gel retardation analysis using a fragment from the 5' upstream region reveals that GT-1 is present in nuclear extracts of etiolated rice leaves and binds to sites conserved between rice and oat phytochrome genes.