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Open Access Research article

Two putative-aquaporin genes are differentially expressed during arbuscular mycorrhizal symbiosis in Lotus japonicus

Marco Giovannetti1, Raffaella Balestrini1, Veronica Volpe1, Mike Guether14, Daniel Straub2, Alex Costa3, Uwe Ludewig2 and Paola Bonfante1*

Author Affiliations

1 Department of Life Sciences and Systems Biology, University of Torino and IPP-CNR, Viale Mattioli 25, Torino, 10125, Italy

2 Institute of Crop Science, University of Hohenheim, Fruwirthstrasse 20, Stuttgart, 70599, Germany

3 Department of Life Sciences, University of Milano, Via Celoria 26, Milano, 20133, Italy

4 Botanical Institute, Karlsruhe Institute of Technology, Hertzstrasse 16, Karlsruhe, D-76187, Germany

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BMC Plant Biology 2012, 12:186  doi:10.1186/1471-2229-12-186

Published: 9 October 2012

Abstract

Background

Arbuscular mycorrhizas (AM) are widespread symbioses that provide great advantages to the plant, improving its nutritional status and allowing the fungus to complete its life cycle. Nevertheless, molecular mechanisms that lead to the development of AM symbiosis are not yet fully deciphered. Here, we have focused on two putative aquaporin genes, LjNIP1 and LjXIP1, which resulted to be upregulated in a transcriptomic analysis performed on mycorrhizal roots of Lotus japonicus.

Results

A phylogenetic analysis has shown that the two putative aquaporins belong to different functional families: NIPs and XIPs. Transcriptomic experiments have shown the independence of their expression from their nutritional status but also a close correlation with mycorrhizal and rhizobial interaction. Further transcript quantification has revealed a good correlation between the expression of one of them, LjNIP1, and LjPT4, the phosphate transporter which is considered a marker gene for mycorrhizal functionality. By using laser microdissection, we have demonstrated that one of the two genes, LjNIP1, is expressed exclusively in arbuscule-containing cells. LjNIP1, in agreement with its putative role as an aquaporin, is capable of transferring water when expressed in yeast protoplasts. Confocal analysis have demonstrated that eGFP-LjNIP1, under its endogenous promoter, accumulates in the inner membrane system of arbusculated cells.

Conclusions

Overall, the results have shown different functionality and expression specificity of two mycorrhiza-inducible aquaporins in L. japonicus. One of them, LjNIP1 can be considered a novel molecular marker of mycorrhizal status at different developmental stages of the arbuscule. At the same time, LjXIP1 results to be the first XIP family aquaporin to be transcriptionally regulated during symbiosis.

Keywords:
Arbusculated cells; Legumes; Aquaporin; Symbiosis; XIP; NIP; Mycorrhizal fungi; Lotus japonicus