Transcriptome Profiling of Lotus japonicus Roots During Arbuscular Mycorrhiza Development and Comparison with that of Nodulation
1 Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
2 Graduate School of Science and Technology, Kagoshima University, Kagoshima 890-0065, Japan
3 Department of Chemistry and BioScience, Kagoshima University, Kagoshima 890-0065, Japan
4 National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8602, Japan
5 Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, Saitama 332-0012, Japan
Received 17 January 2007 ; accepted 22 June 2007.
To better understand the molecular responses of plants to arbuscular mycorrhizal (AM) fungi, we analyzed the differential gene expression patterns of Lotus japonicus, a model legume, with the aid of a large-scale cDNA macroarray. Experiments were carried out considering the effects of contaminating microorganisms in the soil inoculants. When the colonization by AM fungi, i.e. Glomus mosseae and Gigaspora margarita, was well established, four cysteine protease genes were induced. In situ hybridization revealed that these cysteine protease genes were specifically expressed in arbuscule-containing inner cortical cells of AM roots. On the other hand, phenylpropanoid biosynthesis-related genes for phenylalanine ammonia-lyase (PAL), chalcone synthase, etc. were repressed in the later stage, although they were moderately up-regulated on the initial association with the AM fungus. Real-time RT–PCR experiments supported the array experiments. To further confirm the characteristic expression, a PAL promoter was fused with a reporter gene and introduced into L. japonicus, and then the transformants were grown with a commercial inoculum of G. mosseae. The reporter activity was augmented throughout the roots due to the presence of contaminating microorganisms in the inoculum. Interestingly, G. mosseae only colonized where the reporter activity was low. Comparison of the transcriptome profiles of AM roots and nitrogen-fixing root nodules formed with Mesorhizobium loti indicated that the PAL genes and other phenylpropanoid biosynthesis-related genes were similarly repressed in the two organs.
Key words: cysteine proteinase; defense response; phenylalanine ammonia-lyase; symbiosis
* To whom correspondence should be addressed. Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan. Tel. +81 75-753-6141. Fax. +81 75-753-6470. E-mail: shing{at}kais.kyoto-u.ac.jp
Current address: Friedrich Miescher Institute, Maulbeerstrasse 66, CH-4058 Basel, Switzerland.
Current address: National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8602, Japan.
¶ Current address: Kazusa DNA Research Institute, Chiba 292-0812, Japan.
Current address: Faculty of Agriculture, Saga University, Saga 840-8502, Japan.
|| Current address: Department of Biotechnological Science, Kinki University, Wakayama 649-6493, Japan.
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