Transcriptional analysis of genes involved in nodulation in soybean roots inoculated with Bradyrhizobium japonicum strain CPAC 15.

Gesiele Almeida Barros De Carvalho,Jesiane Stefânia Silva Batista,Mariangela Hungria,Francismar Corrêa Marcelino-Guimarães,Leandro Costa Do Nascimento

doi:10.1186/1471-2164-14-153

Abstract

BackgroundBiological nitrogen fixation in root nodules is a process of great importance to crops of soybean [Glycine max (L.) Merr.], as it may provide the bulk of the plant’s needs for nitrogen. Legume nodulation involves several complex steps and, although studied for many decades, much remains to be understood.ResultsThis research aimed at analyzing the global expression of genes in soybean roots of a Brazilian cultivar (Conquista) inoculated with Bradyrhizobium japonicum CPAC 15, a strain broadly used in commercial inoculants in Brazil. To achieve this, we used the suppressive subtractive hybridization (SSH) technique combined with Illumina sequencing. The subtractive library (non-inoculated x inoculated) of soybean roots resulted in 3,210 differentially expressed transcripts at 10 days after inoculation were studied. The data were grouped according to the ontologies of the molecular functions and biological processes. Several classes of genes were confirmed as related to N2 fixation and others were reported for the first time.ConclusionsDuring nodule formation, a higher percentage of genes were related to primary metabolism, cell-wall modifications and the antioxidant defense system. Putative symbiotic functions were attributed to some of these genes for the first time.

Highlights

Biological nitrogen fixation in root nodules is a process of great importance to crops of soybean [Glycine max (L.) Merr.], as it may provide the bulk of the plant’s needs for nitrogen
This study aimed at analyzing the global expression of genes in soybean roots of cultivar Conquista inoculated with B. japonicum strain CPAC 15 (=SEMIA 5079), both broadly used in Brazil, through the suppressive subtractive hybridization (SSH) technique [12] combined with sequencing Illumina analysis
The SSH library of the Brazilian cultivar Conquista, at 10 days after inoculation (DAI) with B. japonicum strain CPAC 15, which is broadly used in commercial inoculants in Brazil, resulted in 4,621,072 reads

Summary

Introduction

Biological nitrogen fixation in root nodules is a process of great importance to crops of soybean [Glycine max (L.) Merr.], as it may provide the bulk of the plant’s needs for nitrogen. The establishment of the symbiosis starts with molecular interactions between the rhizobia and the host plant, involving a succession of complex processes that lead to profound changes in both symbionts [3,6]. The plant releases molecular signals, in particular flavonoid compounds, that are primary inducers of rhizobial nodulation genes The induction of this class of genes leads to the biosynthesis of Nod factors, rhizobial signals that trigger specific responses in the root hairs of the host plant; plant cells perceive the presence of Nod factors— and of the rhizobia—through cell-surface receptors on the roots [7,8,9,10]. Many molecular events are triggered in a coordinated manner, leading to morphological and physiological changes in the host plant, necessary for a successful symbiosis [3]

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