Abstract
BackgroundLegume-rhizobium symbiosis is a complex process that is regulated in the host plant cell through gene expression network. Many nodulin genes that are upregulated during different stages of nodulation have been identified in leguminous herbs. However, no nodulin genes in woody legume trees, such as black locust (Robinia pseudoacacia), have yet been reported.Methodology/Principal findingsTo identify the nodulin genes involved in R. pseudoacacia-Mesorhizobium amorphae CCNWGS0123 symbiosis, a suppressive subtractive hybridization approach was applied to reveal profiling of differentially expressed genes and two subtracted cDNA libraries each containing 600 clones were constructed. Then, 114 unigenes were identified from forward SSH library by differential screening and the putative functions of these translational products were classified into 13 categories. With a particular interest in regulatory genes, twenty-one upregulated genes encoding potential regulatory proteins were selected based on the result of reverse transcription-polymerase chain reaction (RT-PCR) analysis. They included nine putative transcription genes, eight putative post-translational regulator genes and four membrane protein genes. The expression patterns of these genes were further analyzed by quantitative RT-PCR at different stages of nodule development.ConclusionsThe data presented here offer the first insights into the molecular foundation underlying R. pseudoacacia–M. amorphae symbiosis. A number of regulatory genes screened in the present study revealed a high level of regulatory complexity (transcriptional, post-transcriptional, translational and post-translational) that is likely essential to develop symbiosis. In addition, the possible roles of these genes in black locust nodulation are discussed.
Highlights
Different leguminous plants interact with appropriate rhizobia genera, leading to the formation of nodules on host plant roots
The data presented here offer the first insights into the molecular foundation underlying R. pseudoacacia–M. amorphae symbiosis
A number of regulatory genes screened in the present study revealed a high level of regulatory complexity that is likely essential to develop symbiosis
Summary
Different leguminous plants interact with appropriate rhizobia genera, leading to the formation of nodules on host plant roots. Rhizobia in root nodules could fix nitrogen to ammonia for plant growth and simultaneously obtain carbohydrates from the plant for sustenance. This perfect, mutually beneficial symbiosis involves a series of complex processes, including rhizobia infection, plant root cell differentiation, nodule formation and nitrogen fixation. Both partners are involved in the interaction by exchanging numerous signal molecules. Invagination of root hairs leads to the formation of infection threads and nodule primordia form from root cortical cells [3]. No nodulin genes in woody legume trees, such as black locust (Robinia pseudoacacia), have yet been reported
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