Plant root transcriptome profiling of Azospirillum-rice cooperation

Cooperation involving Plant Growth-Promoting Rhizobacteria results in improvements of plant growth and health. While pathogenic and symbiotic interactions are known to induce transcriptional changes for genes related to plant defense and development, little is known about the impact of phytostimulating rhizobacteria on plant gene expression. In this context, this study aimed at identifying genes significantly regulated in rice roots upon Azospirillum inoculation, considering possible favored interaction between a strain and its original host cultivar. Genome-wide analyses of root gene expression of Oryza sativa japonica cultivars Cigalon and Nipponbare were performed, by using microarrays, seven days post inoculation with A. lipoferum 4B (isolated from Cigalon roots) or Azospirillum sp. B510 (isolated from Nipponbare) and compared to the respective non-inoculated condition. For each of the four condition, three replicates were analysed on an oligo microarray produced by NimbleGenTM (Madison, WI, USA). The microarray was derived of the one previously described in Yuan et al. 2005 . This microarray is composed of about 385,000 60mer probes selected for their GC content, Tm and number of cycles needed to synthesize the oligo. This chip contains 90,000 probes representing 45,000 genes (two probes per gene) of rice Oryza sativa ssp. japonica, based on the TIGR rice genome annotation version 3.1 genes (Chaparro et al. 2007) and 201 691 oligomers corresponding to previously described copies of LTR retrotranposons available on the retrOryza database (www.retroryza.fr). Probes represent 1,000 bp of the LTR-retrotransposon flanking regions at the 3’ and 5’ side. The oligonucleotides have been designed at the 3’ end of the genes to detect the readings of reverse transcriptase. On the other hand, the LTR-retrotransposons are represented throughout their length at the rate of a probe every 500 bp.