Isolation and Characterization of Rice Phytochrome A Mutants

Abstract

To elucidate phytochrome A (phyA) function in rice, we screened a large population of retrotransposon ( Tos17 ) insertional mutants by polymerase chain reaction and isolated three independent phyA mutant lines. Sequencing of the Tos17 insertion sites confirmed that the Tos17 s interrupted exons of PHYA genes in these mutant lines. Moreover, the phyA polypeptides were not immunochemically detectable in these phyA mutants. The seedlings of phyA mutants grown in continuous far-red light showed essentially the same phenotype as dark-grown seedlings, indicating the insensitivity of phyA mutants to far-red light. The etiolated seedlings of phyA mutants also were insensitive to a pulse of far-red light or very low fluence red light. In contrast, phyA mutants were morphologically indistinguishable from wild type under continuous red light. Therefore, rice phyA controls photomorphogenesis in two distinct modes of photoperception-far-red light-dependent high irradiance response and very low fluence response-and such function seems to be unique and restricted to the deetiolation process. Interestingly, continuous far-red light induced the expression of CAB and RBCS genes in rice phyA seedlings, suggesting the existence of a photoreceptor(s) other than phyA that can perceive continuous far-red light in the etiolated seedlings. INTRODUCTIONLight is one of the most important environmental stimuli that plays a pivotal role in the regulation of plant growth, development, and metabolic activities. The perception of environmental light by plants is achieved by a family of plant photoreceptors that includes the phytochromes (Neff et al., 2000), cryptochromes, and several others (Briggs and Huala, 1999), which are capable of detecting a wide spectrum of light wavelengths ranging from UV to far-red light.Physiological and photochemical studies in recent decades have shown that presumed phytochrome-mediated responses in plants can be classified into three different response modes: red (R)/far-red (FR) reversible responses designated the low fluence response (LFR) and two other responses named the very low fluence response (VLFR) and the high irradiance response (HIR) according to their energy requirements (Mohr, 1962;Briggs et al., 1984). In a typical LFR, plants respond to 1 to 1000 mol m Ϫ 2 of R light, whereas the VLFR requires only 0.1 to 1 mol m Ϫ 2 of R light. The HIR requires prolonged exposure to light of relatively high photon flux and shows fluence rate dependence. Action spectra for VLFR, LFR (Shinomura et al., 1996), and HIR (Shinomura et al., 2000) using phytochrome-deficient mutants of Arabidopsis showed that phyA is the principal photoreceptor involved in the VLFRs, such as induction of seed germination (Shinomura et al., 1996) and CAB gene expression (Hamazato et al., 1997), and the FR light-induced HIRs, including inhibition of hypocotyl elongation (Quail et al., 1995;Shinomura et al., 2000). On the other hand, phyB controls LFR in a R/FR reversible mode.Phytochromes in higher plants are encoded by a small gene famil...

Highly efficient production and characterization of T-DNA plants for rice (Oryza sativa L.) functional genomics

“…Recently, insertions within genes coding for a rice phytochrome A (OsphyA) and an homeobox (Osh15) protein have been identified in the tos17 rice mutant population (Sato et al 1999;Takano et al 2001). When the genome sequence of a plant species is available, systematic characterization of the insertion from each mutant is an alternative approach for reverse genetic studies.…”

Phytochrome A requires jasmonate for photodestruction

“…An isogenic sister line homozygous for the wild type allele was used as reference throughout the study. The phyA mutant (Takano et al 2001) was obtained in the two japonica cultivars 'Nipponbare NC-5' and 'Akita-komachi A2'.…”

“…The speciWcity of the signals obtained by Western blot was veriWed by using the phyA mutant (Takano et al 2001) as negative control. None of the antibodies raised against phyA from Arabidopsis or pea recognized any signals in rice extracts (data not shown), whereas the antibodies mAR07 and mAR08 raised against phyA from rye (Nagatani et al 1987) could be used to detect rice phyA with identical results (Fig.…”

“…Each time course was repeated at least 3 times at diVerent days. Western blot analysis related to the examination of the eVect of JA on phyA degradation was performed as described in Takano et al (2001).…”

Overexpression of a phytochrome-regulated tandem zinc finger protein gene, OsTZF1, confers hypersensitivity to ABA and hyposensitivity to red light and far-red light in rice seedlings

“…The phyA (phyA4), phyB (phyB1) phyAphyB (phyA4phyB1), and phyAphyC (phyA4phyC1) mutants were previously described (Takano et al 2001;Takano et al 2005). The genetic background of WT and phytochrome mutants was Oryza sativa L., cv Nipponbare.…”