Regulation of the pericycle proteome in maize (Zea mays L.) primary roots by RUM1 which is required for lateral root initiation

Lateral roots are all roots that are initiated in the pericycle cell layer of other roots during postembryonic development. The maize (Zea mays L.) mutant rum1 (rootless with undetectable meristems 1) does not initiate lateral roots in the primary root. In the present study, two-dimensional electrophoresis proteome profiles of three biological replicates of pericycle cells isolated from the differentiation zone of 2.5-day-old wild-type and rum1 primary roots were generated. This early developmental stage was selected in order to analyze histologically similar cells before the initiation of lateral roots in wild-type primary roots. In total, 418 proteins were reproducibly detected on all six gels after fluorescent staining with Flamingo dye. Among those, twelve proteins were differentially accumulated between wild-type and rum1 pericycle cells (Fc > 2; p < 0.05). Electrospray ionization tandem mass spectrometry (ESI-MS/MS) identified eight of the twelve proteins. Six proteins were related to metabolism, one protein belonged to the class of disease and defense, and one protein was related to development. Six of the eight proteins have not been previously localized to the pericycle. Moreover, the slight overlap between proteins and transcripts that are differentially accumulated in the maize pericycle between wild-type and rum1 underscores the importance of posttranscriptional protein modifications that cannot be detected on the RNA level. The differential accumulation of proteins in rum1 and wild-type pericycle cells of the primary root suggests that the abundance of these proteins could be regulated by RUM1.