Published Papers - ARAKI Ryoichi

A Novel Barley Yellow Stripe 1-Like Transporter (HvYSL2) Localized to the Root Endodermis Transports Metal-Phytosiderophore Complexes

Ryoichi Araki, Jun Murata, Yoshiko Murata （Part： Lead author )

PLANT AND CELL PHYSIOLOGY ( OXFORD UNIV PRESS )  52 ( 11 ) 1931 - 1940   2011.11  [Refereed]

　View Summary

Recent advances in our understanding of how graminaceous plants take up insoluble forms of iron from the rhizosphere and mobilize them in plant tissues are primarily based on the identification of various transporters that are specific to metal-phytosiderophore (PS) complexes containing mugineic acid and deoxymugineic acid. Barley (Hordeum vulgare L.) yellow stripe 1 (HvYS1) is a metal-PS transporter that preferentially transports Fe(III)-PS compared with other metal complexes. Here, we report the cloning and characterization of HvYSL2, a novel metal-PS transporter encoding gene. HvYSL2 is composed of 702 amino acids with 14 transmembrane domains, which are conserved among this class of transporters, and exhibits 67.3% identity to HvYS1. Electrophysiological experiments with Xenopus laevis oocytes revealed that HvYSL2 transports PS complexes with Fe(III), Zn(II), Ni(II), Cu(II), Mn(II) or Co(II); this constitutes a broader range of substrate preference than HvYS1. Real-time PCR analysis revealed that HvYSL2 mRNA is expressed in shoots and also in roots, where it is induced under iron-deficient conditions. Moreover, immunohistochemistry in roots revealed that HvYSL2 is localized to the endodermis, whereas HvYS1 is expressed primarily in the epidermis. These data suggest that HvYSL2 is spatially distinct from HvYS1 and plays a unique role in delivering a broad range of essential metals in barley.

DOI

High-affinity nitrate uptake by rice (Oryza sativa) coleoptiles

Shu Takayanagi, Yuma Takagi, Ryoichi Araki, Hiroshi Hasegawa

JOURNAL OF PLANT RESEARCH ( SPRINGER TOKYO )  124 ( 2 ) 305 - 309   2011.03  [Refereed]

　View Summary

Nitrate uptake by rice coleoptiles was evaluated using (15)N-nitrate in relation to the expression of high-affinity nitrate uptake-related genes, OsNRT2s (OsNRT2.1-2.4) and OsNAR2s (OsNAR2.1 and 2.2). Apparent nitrate uptake by coleoptiles was about one-sixth of that by hydroponically cultured seedling roots. Real-time RT-PCR analysis revealed that OsNRT2.1, a root-specific key gene of inducible high-affinity transport system for nitrate, was most strongly induced in coleoptiles following nitrate supply initiation, while other OsNRT2s and OsNAR2s showed modest induction. These results suggest that rice coleoptiles may have high-affinity transport systems for nitrate similar to roots, and can be model organs for nutrient uptake by submerged plant shoots.

DOI

Omics-based identification of Arabidopsis Myb transcription factors regulating aliphatic glucosinolate biosynthesis

Masami Yokota Hirai, Kenjiro Sugiyama, Yuji Sawada, Takayuki Tohge, Takeshi Obayashi, Akane Suzuki, Ryoichi Araki, Nozomu Sakurai, Hideyuki Suzuki, Koh Aoki, Hideki Goda, Osamu Ishizaki Nishizawa, Daisuke Shibata, Kazuki Saito

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA ( NATL ACAD SCIENCES )  104 ( 15 ) 6478 - 6483   2007.04  [Refereed]

　View Summary

Understanding plant metabolism as an integrated system is essential for metabolic engineering aimed at the effective production of compounds useful to human life and the global environment. The "omics" approach integrates transcriptome and metabolome data into a single data set and can lead to the identification of unknown genes and their regulatory networks involved in metabolic pathways of interest. one of the intriguing, although poorly described metabolic pathways in plants is the biosynthesis of glucosinolates (GSLs), a group of bioactive secondary products derived from amino acids that are found in the family Brassicaceae. Here we report the discovery of two R2R3-Myb transcription factors that positively control the biosynthesis of GSLs in Arabidopsis thaliana by an integrated omics approach. Combined transcriptome coexpression analysis of publicly available, condition-independent data and the condition-specific (i.e., sulfur-deficiency) data identified Myb28 and Myb29 as candidate transcription factor genes specifically involved in the regulation of aliphatic GSL production. Analysis of a knockout mutant and ectopic expression of the gene demonstrated that Myb28 is a positive regulator for basal-level production of aliphatic GSLs. Myb29 presumably plays an accessory function for methyl jasmonate-mediated induction of a set of aliphatic GSL biosynthetic genes. Overexpression of Myb28 in Arabidopsis-cultured suspension cells, which do not normally synthesize GSLs, resulted in the production of large amounts of GSLs, suggesting the possibility of efficient industrial production of GSLs by manipulation of these transcription factors. A working model for regulation of GSL production involving these genes, renamed Production of Methionine-Derived Glucosinolate (PMG) 1 and 2, are postulated.

DOI

Expression of rice (Oryza sativa L.) genes involved in high-affinity nitrate transport during the period of nitrate induction

Ryoichi Araki, Hiroshi Hasegawa （Part： Lead author )

BREEDING SCIENCE ( JAPANESE SOC BREEDING )  56 ( 3 ) 295 - 302   2006.09  [Refereed]

　View Summary

When breeding crops that utilize nitrogen efficiently, it is important to reveal the regulation of nitrate uptake at the molecular level. We focused on the expression of two nitrate uptake-related genes, NRT2 and NAR2, and nitrate uptake during the nitrate induction. Four rice NRT2s (OsNRT2.1 similar to 2.4) and two NAR2s (OsNAR2.1 similar to 2.2) were identified in the rice genome database. We analyzed the expression of the genes in the roots and shoots after supply of nitrate with or without ammonium pretreatment by the RT-PCR method. The apparent nitrate uptake was also measured. Differential expression of OsNRT2.1 and OsNRT2.2, which have the same ORF with different 5'- and 3'-UTR, was observed in the seedlings pretreated with ammonium. The apparent nitrate uptake synchronously increased after supply of nitrate with the expression pattern of OsNRT2.1 in roots either with or without ammonium pretreatment. The expression of OsNAR2.1, which is thought to be an activator gene for the function of NRT2, was also coordinated with that of OsNRT2.1. On the other hand, OsNRT2.2 was already expressed after ammonium pretreatment, suggesting that OsNRT2.2 would be transcribed to take up nitrate in flooded soils. The present results indicate that OsNRT2.1, OsNRT2.2 and OsNAR2.1 are candidate genes when breeding for efficient use of nitrate in rice.

DOI

ヨシ（Phragmites australis）の遺伝的改良－序論－

長谷川博, 荒木良一, 野見山誉, 宮角裕喜, 玉井紀子, 伴あずさ

近畿作物・育種研究 51: 13-17.     2006  [Refereed]

Genetic differences in nitrate uptake in two clones of the common reed, Phragmites australis

R Araki, M Mori, H Hasegawa （Part： Lead author )

BREEDING SCIENCE ( JAPANESE SOC BREEDING )  55 ( 3 ) 297 - 302   2005.09  [Refereed]

　View Summary

Phragmites australis, common reed, could be useful in removing eutrophic substances from river and lake water. In this study, the genetic differences in nitrate uptake ability of the reed were investigated with a view to breeding a reed plant useful for phytoremediation. Two reed clones (W-6 and W-8) isolated from a reed community in the lakeside wetland along Lake Biwa, Japan, were used for a study on the physiological and molecular basis of nitrate uptake. K(m)s for nitrate uptake were 80.8 and 45.2 mu M and V(max)s for nitrate uptake were 10.62 and 2.37 mu mol g(-1) root f.w. h(-1) in W-6 and W-8, respectively, suggesting that there were critical differences in kinetic parameters for nitrate uptake. To investigate these differences at the molecular level, we isolated a high-affinity nitrate transporter gene (NRT2) from the two reed clones and analyzed the reed NRT2 structure and expression. The deduced amino acid sequence of the reed NRT2 consisted of 523 residues and had a high similarity to NRT2 from other monocots. Reed NRT2 was strongly expressed in roots treated with 200 mu M nitrate. There were three amino acid substitutions of the reed NRT2 between W-6 and W-8. Differences in NRT2 transcription were also observed between the two clones. It was not clear whether the difference in kinetic parameters for nitrate was due to the reed NRT2 structure or expression. These results indicate the possibility of selecting genotypes more useful for the removal of nitrate.

DOI

イネにおける硝酸吸収および硝酸還元酵素活性の遺伝解析.

東明沙, 荒木良一, 山内裕香, 長谷川博

近畿作物・育種研究 49: 17-20.     2004  [Refereed]

ヨシ(Phragmites australis)の高親和性硝酸トランスポーター遺伝子(NRT2)について.

荒木良一, 森真理, 森正之, 長谷川博 （Part： Lead author )

近畿作物・育種研究 48: 57-59.     2003  [Refereed]