Identification of differentially expressed proteins in soybean nodules under phosphorus deficiency through proteomic analysis.

Symbiotic nitrogen fixation is a high-phosphorus demand process. Proteomic analysis was performed to identify the differentially expressed proteins in soybean nodules under phosphate starvation, and qRT-PCR was subsequently conducted to examine the expression patterns of the genes encoding the identified proteins. There were 44 phosphate-starvation responsive proteins identified from soybean nodules. Among them, 14 plant and 3 rhizobial proteins were up-regulated, whereas 13 plant and 14 rhizobial proteins were down-regulated by phosphate starvation. The qRT-PCR assays verified that gene expression correlated with 11 of the 14 up-regulated proteins from plants, but only 4 of 13 down-regulated proteins were correlated to the expression of the corresponding genes, suggesting that most up-regulated proteins may be controlled at the transcriptional level, whereas down-regulated proteins were controlled at the post-transcriptional level. Furthermore, a group of genes exhibited differential responses to phosphate starvation in nodules versus roots, suggesting that different adaptive responses might occur between roots and nodules. To our best knowledge, this is the first study to reveal differential protein profiles of nodules responding to phosphate starvation through proteomic analysis, which could result in a relatively comprehensive understanding of molecular mechanisms through which soybean nodules adapt to phosphorus stress.