Abstract
Root hairs are single tubular cells formed from the differentiation of epidermal cells on roots. They are involved in water and nutrient uptake and represent the infection site on leguminous roots by rhizobia, soil bacteria that establish a nitrogen-fixing symbiosis. Root hairs develop by polar cell expansion or tip growth, a unique mode of plant growth shared only with pollen tubes. A more complete characterization of root hair cell biology will lead to a better understanding of tip growth, the rhizobial infection process, and also lead to improvements in plant water and nutrient uptake. We analyzed the proteome of isolated soybean (Glycine max) root hair cells using two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and shotgun proteomics (1D-PAGE-liquid chromatography and multidimensional protein identification technology) approaches. Soybean was selected for this study due to its agronomic importance and its root size. The resulting soybean root hair proteome reference map identified 1,492 different proteins. 2D-PAGE followed by mass spectrometry identified 527 proteins from total cell contents. A complementary shotgun analysis identified 1,134 total proteins, including 443 proteins that were specific to the microsomal fraction. Only 169 proteins were identified by the 2D-PAGE and shotgun methods, which highlights the advantage of using both methods. The proteins identified are involved not only in basic cell metabolism but also in functions more specific to the single root hair cell, including water and nutrient uptake, vesicle trafficking, and hormone and secondary metabolism. The data presented provide useful insight into the metabolic activities of a single, differentiated plant cell type.
Highlights
Root hairs are single tubular cells formed from the differentiation of epidermal cells on roots
The formation of a single root hair cell from an epidermal cell can be divided into several stages, including cell fate specification, root hair initiation, and tip growth, leading to maturity and functionality (Gilroy and Jones, 2000)
Individual protein spots separated by 2DPAGE were excised from the gel and their derivatized peptides analyzed by matrix-assisted laser-desorption ionization time of flight/time of flight (MALDI-TOF/ TOF) mass spectrometry (MS), whereas proteins and their derivatized peptides separated by 1D-PAGE and LC/LC were analyzed en mass using an ion trap mass spectrometer
Summary
Root hairs are single tubular cells formed from the differentiation of epidermal cells on roots They are involved in water and nutrient uptake and represent the infection site on leguminous roots by rhizobia, soil bacteria that establish a nitrogen-fixing symbiosis. The proteins identified are involved in basic cell metabolism and in functions more specific to the single root hair cell, including water and nutrient uptake, vesicle trafficking, and hormone and secondary metabolism. Root hairs represent the preferred infection site for rhizobia on legume roots This symbiotic interaction results in the formation of a nodule in which bacteria fix atmospheric nitrogen that can be utilized by the plant (Stacey et al, 2006). A protein reference map was developed for soybean leaves, identifying 119 proteins (Xu et al, 2006a)
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