Analysis of a non-nodulating Arachis hypogaea L. Whole-Root Proteome Identifies Changes Associated with Host-Rhizobia Interaction

Abstract

More than forty plant proteins have been associated with symbiotic N2 fixation, a process important for legume crop production. In peanut, rhizobia enter by more primitive root crack entry rather than through root hairs. To survey global changes in this system before nodule maturation, a whole-root proteome analysis was performed using 17-day-old wild-type and non-nodulating Arachis hypogaea. Tandem mass tag (TMT) six-plex labeling enabled simultaneous, LC-MS/MS comparison of triplicate samples, with and without Bradyrhizobium sp. inoculation. Using sequence from A. hypogaea diploid progenitors as a reference, >2000 protein families were identified per assay. Significant differences included a patatin-like protein with 2.62 and 14.52 fold higher abundance in uninoculated and inoculated roots of wild-type genotype E6+ compared to non-nodulating genotype E7-, respectively. A peroxidase and thaumatin-like protein recently identified by RNA-seq to have >2X transcript abundance in E6+ vs. E7- post-inoculation were similarly found in lower abundance in E7-. Conversely, aspartic proteinase and apoptosis-inducing factor family members were among proteins with higher abundance in uninoculated and inoculated E7-. Bradyrhizobium sp. peptides were generally in higher abundance in inoculated E6+, suggesting that early host-rhizobia interaction may be compromised in inoculated, non-nodulating E7-. Interestingly, many proteins with putative symbiotic roles identified in uninoculated wild-type and non-nodulating pairs (E4−/E5+ and E6+/E7-) were absent from 17-day-old, inoculated E6+ and E7-. The differentially represented proteins identified provide insight into the early stages of peanut nodulation.