Os03g0323200
- The rice gene Os03g0323200 was reported as OsCHLH in 2003[1]. The OsCHLH gene could encode a protein of 1,388 amino acids with a putative N-terminal chloroplast transit peptide.
Contents
Annotated Information
Function
- The OsCHLH gene encodes the largest subunit of the rice Mg-chelatase, a key enzyme in the chlorophyll branch of the tetrapyrrole biosynthetic pathway[1].
- Transcript levels of the OsCHLH gene are increased by light. The researchers also found this induction by assaying the fusion product between OsCHLH and GUS[1].
- The OsCHLH gene is essential for rice plants. Knockout mutations of this gene result in a seedling-lethal phenotype. DNA gel-blot analysis of rice genomic DNA indicates only a single copy of the gene[1].
- The researchers suggest that the C-terminal region is essential for CHLH enzyme activity. Based on the RGP mapping data, OsCHLH is positioned near the chl2 locus on Chromosome 3[1].
Mutation
- Light microscopic observation of the cross-section of the chlorina mutant leaf blade did not show any significant change in the size or number of mesophyll cells (data not known). However, TEM analysis revealed that, although there was no change in the number of chloroplasts, their shape in the OschlH mutant was irregular compared with the wild-type chloroplasts (Fig. 1). The knockout mutant did not show dispersal of prolamella bodies and retained the appearance of an etioplast in the continuous light condition. Thylakoid membranes in the mutant chloroplasts also were severely disrupted. The reduction of light harvesting complexes in the thylakoid membrane due to the lack of chlorophyll synthesis may disrupt the thylakoid ultrastructure in the mutant[1].
Fig. 1 TEM analysis of the OschlH mutant and wild-type chloroplasts. (A), (C), and (E) are sections of OschlH mutant chloroplasts; (B), (D), and (F) are sections of wild-type chloroplasts. Scale bars = 1 μm; open arrow, thylakoid membrane; filled arrow, prolamellar body; Cp, chloroplast. [1].
- The researchers measured chlorophyll contents in 10-day-old seedlings (Table 1). In wild-type and the heterozygotic plants, the ratio between chlorophyll a and chlorophyll b was about three [2]. However, in homozygotic plants, the levels of chlorophylls were very low, indicating lack of chlorophyll biosynthesis[1].
Table 1 Chlorophyll contents of wild-type, heterozygous, and homozygous plants [1].
Expression Pattern
- Gus assays were conducted in seedlings of the T3 heterozygotic plants that were grown under either continuous light or in the dark. GUS-activity was light inducible in the coleoptiles, leaves, and roots of the light-grown seedlings (Fig. 2A, B). Dark-grown seedlings showed a low level of GUS activity, primarily in the scutellum tissue, indicating that a basal level of the OsCHLH transcript still exists under darkness. The crosssection of the light-grown seedlings showed that GUS activity was prominent in the cortical tissues of the roots (Fig. 2C) and in the mesophyll cells of the coleoptiles (Fig. 2D). In the immature flower, GUS activity was observed primarily in the palea/lemma, while in the mature flower, the fusion gene was expressed strongly in the palea/lemma and weakly in the ovary (Fig. 2E, F). In the leaves of 15-day-old seedlings, expression was confined to the mesophyll cells (Fig. 2G)[1].
Fig. 2 Analysis of the tagged-gene expression patterns using GUS assay. [1].
Evolution
- The OsCHLH gene could encode a protein of 1,388 amino acids with a putative N-terminal chloroplast transit peptide
(Fig. 3). A calculated molecular mass of 154 kDa corresponds to the size of the homologous precursor CHLH protein from higher plants (Hudson et al. 1993, Gibson et al. 1996, Jensen et al. 1996). Compared with other CHLH sequences, the OsCHLH protein has 88% identity with the barley XANTHA-F subunit, 84% with the soybean CHLH, 82% with the garden snapdragon CHLH, 81% with the tobacco CHLH, and 81% with the Arabidopsis thaliana CHLH. Although the N-terminal regions (1st to ~49th residues) of CHLHs are variable, the remaining regions are highly conserved (Fig. 3)[1].
Fig. 3 Predicted amino acid sequence of OsCHLH. The sequence was multiple-aligned with Arabidopsis CHLH (Z68495), soybean CHLH (AJ001091), tobacco CHLH (AF014052), and barley XANTHAF (U26916). [1].
Labs working on this gene
- National Research Laboratory of Plant Functional Genomics, Division of Molecular and Life Sciences, Pohang University of Science and
Technology (POSTECH), Pohang, 790-784 Republic of Korea
- School of Life Sciences and Biotechonology, Korea University, Seoul, 136-701 Republic of Korea
- Department of Molecular Genetics, National Institute of Agrobiological Resources, Tsukuba, Ibaraki, 305-8602 Japan
References
- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 Jung KH, Hur J, Ryu CH, Choi Y, Chung YY, Miyao A, Hirochika H, An G. Characterization of a rice chlorophyll-deficient mutant using the T-DNA gene-trap system. Plant Cell Physiol. 2003 May;44(5):463-72. PubMed PMID: 12773632.
- ↑ Yamazaki, J., Kamimura, Y., Okada, M. and Sugimura, Y. (1999) Changes in photosynthetic characteristics and photosystem stoichiometries in the lower leaves in rice seedlings. Plant Sci. 148: 155–163.
