Molecular Characterization of LjABCG1, an ATP-Binding Cassette Protein in Lotus japonicus.

Akifumi Sugiyama,Shusei Sato,Mari Narusaka,Mikiko Kojima,Shoju Fukuda,Hitoshi Sakakibara,Masayoshi Kawaguchi,Kojiro Takanashi,Yoshihiro Narusaka,Kazufumi Yazaki,Nobukazu Shitan,Miki Yoshioka,Satoshi Tabata,Hirofumi Yoshioka,Keqiang Wu

doi:10.1371/journal.pone.0139127

Abstract

LjABCG1, a full-size ABCG subfamily of ATP-binding cassette proteins of a model legume, Lotus japonicus, was reported as a gene highly expressed during the early stages of nodulation, but have not been characterized in detail. In this study we showed that the induction of LjABCG1 expression was remarkable by methyl jasmonate treatment, and reporter gene experiments indicated that LjABCG1 was strongly expressed in the nodule parenchyma and cell layers adjacent to the root vascular tissue toward the nodule. LjABCG1 was suggested to be localized at the plasma membrane based on the fractionation of microsomal membranes as well as separation via aqueous two-phase partitioning. The physiological functions of LjABCG1 in symbiosis and pathogenesis were analyzed in homologous and heterologous systems. LjABCG1 knock-down L. japonicus plants did not show clear phenotypic differences in nodule formation, and not in defense against Pseudomonas syringae, either. In contrast, when LjABCG1 was expressed in the Arabidopsis pdr8-1 mutant, the penetration frequency of Phytophthora infestans, a potato late blight pathogen, was significantly reduced in LjABCG1/pdr8-1 than in pdr8-1 plants. This finding indicated that LjABCG1, at least partially, complemented the phenotype of pdr8 in Arabidopsis, suggesting the multiple roles of this protein in plant-microbe interactions.

Highlights

ATP-binding cassette (ABC) proteins, which are ubiquitous in all prokaryotes and eukaryotes, constitute one of the largest families in plants, functioning as transporters, channel regulators, and molecular switches
We previously showed that LjABCG1
CM0026.74) belongs to a cluster of full-size ABCG transporter genes, characteristic of the Lotus genome, and that its expression was up-regulated in the nodulated roots of mature plants [18]. cDNA array analysis revealed that LjABCG1 is induced during an early stage of nodulation [17], and tissue-specific expression analysis revealed that LjABCG1 is expressed

Summary

Introduction

ATP-binding cassette (ABC) proteins, which are ubiquitous in all prokaryotes and eukaryotes, constitute one of the largest families in plants, functioning as transporters, channel regulators, and molecular switches. The full-size ABCG subfamily of ABC proteins is found in plants, fungi, oomycetes, brown algae and slime molds, but not in the genomes of bacteria and animals [1,2] [3]. In addition to being involved in heavy metal tolerance and plant signal molecule transport [4,5,6,7], full-size ABCG proteins have been shown to function in response to plant pathogens. A knock-out mutant of this gene showed a high frequency of penetration by the oomycete pathogen Phytophthora infestans, suggesting that AtABCG36 is involved in plant surface resistance to penetration by this pathogen [10]

Methods

Results

Conclusion