Os07g0682800

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Annotated Information

Root hairs, projections from the epidermal cells of the roots, are contributing to water and nutrient uptake and anchorage to the soil.

Function

Root hairs, projections from the epidermal cells of the roots, are contributing to water and nutrient uptake and anchorage to the soil.. SEM observation showed that in rth1 plants, root hair elongation was abolished after the formation of bulge. High-resolution mapping using 2,088 segregants revealed three predicted genes in a 38-kb candidate interval on chromosome 7. Sequences comparison of the three genes between wild-type Oochikara and rth1 detected a nucleotide substitution only in apyrase (OsAPY). This nucleotide substitution (G→A) lies in the junction between the third intron and the forth exon, and results in the splicing anomaly to the rth1 cDNA sequence. Transgenic plants with introduced OsAPY allele restored normal root hairs and plant growth, showing a complementation of rth1 phenotype. We concluded that the root hairless phenotype of rth1 is caused by a mutation of OsAPY. OsAPY appears to be an important gene for root hair elongation and plant growth in rice.

Expression

In Arabidopsis, a lot of root hair mutants are available, and many genes involved in the root hair morphogenesis have been isolated (Grierson and Schiefelbein 2002). On the other hand, rice has a more complicated pattern of root hair formation (Kawata and Ishihara 1959). Only two root hair mutants in rice have been reported (Suzuki et al. 2003, Kim et al. 2007), and, causal gene was isolated in only one mutant (Kim et al. 2007). A mutant gene, root hairless 1 (rth1) reported by Suzuki et al. (2003), remains unidentified. Thus, genetic studies on root hairs in rice lag behind compared to Arabidopsis. In the present study, we have identified a new root hair mutant gene, rth1 in rice by means of positional cloning. We describe morphological and physiological characteristics, and gene expression pattern in rth1 mutant. We revealed that RTH1 encodes an enzyme apyrase that can hydrolyze NTPs and/or diphosphates (Shibata et al. 1999) and that apyrase is a key gene for root hair elongation and plant growth in rice.

Evolution

    F1 progeny derived from a cross between  rth1 and Kasalath showed normal root hairs and plant growth. F2 progeny segregated 1561 plants with normal phenotype and 527 root-hairless plants with short root phenotype, fitting to a 3 : 1 ratio (χ 2 =0.80, 0.3<p<0.4). Therefore, rth1 is considered a recessive mutation. In a population of 116 F2 plants, the rth1 gene mapped roughly to the distal region of the long arm of chromosome 7. For fine mapping, a total of 2,088 F2 plants were studied. The  rth1 gene was flanked by STS markers, RK30 and RK20, with the distances of 0.26cM and 0.05 cM, respectively (Fig. 3A). The physical distance between them is about 38 kb. In the rth1 candidate region,

three genes are predicted in public databases. Those includenucleic acid binding protein (AK109592), expressed protein (AK065098) and putative apyrase protein (AK066262). The entire coding region of all these genes was sequenced.Comparison of the DNA sequences between WT and rth1 detected a single nucleotide change only in the putative apyrase(OsAPY; ATPdiphosphohydrolase EC.3.6.1.5) gene, and the sequences of two other genes are identical between WT and rth1. Compared to the OsAPY gene of WT, rth1 carries a nucleotide substitution (G→A) in the junction between the third intron and the forth exon (Fig. 3C, D). This substitution caused the splicing anomaly to the rth1 cDNA sequence that shifted the splicing site 5-bp downstream and produced a premature stop codon, resulting in 185-amino acid peptide instead of normal 467-amino acid protein. We confirmed alternation of splicing in rth1 by cDNA sequencing.

  we demonstrated that the root hairless phenotype of rth1 is caused by a mutation of OsAPY on chromosome 7.. Also, our SEM observation showed that, in rth1, tip growth is abolished after the formation of bulges.In rice, another root hair mutant gene was isolated: mutation of  cellulose synthase-like D1 gene (OsCSLD1) on chromosome 10, showed short root hair phenotype (Kim  et al. 2007). Role of OsCSLD1 in root

hair elongation was identified based on homology to an Arabidopsis cellulose synthase-like D3 gene.Two apyrase proteins are present in both rice and Arabidopsis. OsAPY and OsAPYL, and AtAPY1 and AtAPY2, were all included in the same group, and each species formed different subgroups.Both genes were expressed in any tissues or stages examined, but expression of OsAPY was significantly reduced in rth1 compared to WT in any tissues or stages studied. Moreover, in seminal root, OsAPY is strongly expressed in apical meristem zone. Therefore, it appears that OsAPY plays important roles in cell division and/or elongation of seminal root.Apyrase catalyzes the hydrolysis of phosphoanhydride bonds of nucleoside tri- and di-phosphates into monophosphates (Shibata et al. 1999). Our genetic experiment showed that, in rice, mutation in OsAPY results in the root hairless phenotype, accompanied by reduced root and shoot growth.

Labs working on this gene

Takahisa Yuo*1, Masanori Toyota1, Masahiko Ichii2 and Shin Taketa3) 1)Faculty of Agriculture, Kagawa University, 2393 Ikenobe, Miki, Kagawa 761-0795, Japan

2) Kagawa University, 1-1 Saiwai, Takamatsu, Kagawa 760-8521, Japan

3) Research Institute for Bioresources, Okayama University, 2-20-1 Chuo, Kurashiki, Okayama 710-0046, Japan

References

1.Cormack,R.G.H. (1935) Investigations on the development of root hairs. New Phytologist 34: 30–54.

2.OsRAF is an ethylene responsive and root abundant factor gene of rice Yibing Hu; Kang Chong; Tai Wang Plant Growth Regulation, 2008, 54(1): 55-61

3.Favery,B., E.Ryan, J.Foreman, P.Linstead, K.Boudonck, M.Steer, P.Shaw and L. Dolan (2001) KOJAK encodes a cellulose synthase-like protein required for root hair cell morphogenesis in Arabidopsis. Genes Dev. 15: 79–89.

4.Gilroy,S. and D.L.Jones (2000) Through form to function: root hair development and nutrient uptake. Trends in Plant Sci. 5: 56–60. Grierson,C. and J. Schiefelbein (2002) The Arabidopsis Book.

5.In: Somerville,C.R. and E.M.Meyerowitz (eds.) Root Hairs, Rockville, MD: American Society of Plant Biologists, (aspb.org/ publications/arabidopsis/) doi: 10.1199/tab.0060, pp.1–22.