The Mucilage Proteome of Maize (Zea mays L.) Primary Roots
ABSTRACT Maize (Zea mays L.) root cap cells secrete a large variety of compounds including proteins via an amorphous gel structure called mucilage into the rhizosphere. In the present study, mucilage secreted by primary roots of 3-4 day old maize seedlings was collected under axenic conditions, and the constitutively secreted proteome was analyzed. A total of 2848 distinct extracellular proteins were identified by nanoLC-MS/MS. Among those, metabolic proteins (approximately 25%) represented the largest class of annotated proteins. Comprehensive sets of proteins involved in cell wall metabolism, scavenging of reactive oxygen species, stress response, or nutrient acquisition provided detailed insights in functions required at the root-soil interface. For 85-94% of the mucilage proteins previously identified in the relatively small data sets of the dicot species pea, Arabidopsis, and rapeseed, a close homologue was identified in the mucilage proteome of the monocot model plant maize, suggesting a considerable degree of conservation between mono and dicot mucilage proteomes. Homologues of a core set of 12 maize proteins including three superoxide dismutases and four chitinases, which provide protection from fungal infections, were present in all three mucilage proteomes investigated thus far in the dicot species Arabidopsis, rapeseed, and pea and might therefore be of particular importance.
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ABSTRACT: The root exudate composition reflects the contradictory-concomitantly attractive and repulsive-behaviour of plants towards soil microorganisms. Plants produce antimicrobial, insecticide and nematicide compounds to repel pathogens and invaders. They also produce border cells that detach from roots and play an important role as biological and physical barrier against aggressors. Plants produce also metabolites used as carbon source resulting in the attraction of phytobeneficial soil microorganisms that help plants in controlling diseases directly via the production of antimicrobial compounds or indirectly via the induction of plant systemic resistance. The root exudates may have a direct impact on carbon and nitrogen cycling, as they exhibit a rhizosphere priming effect towards soil organic matter degraders, and may inhibit nitrification process by soil nitrifying microorganisms. They also contain signalling molecules required for the establishment of ‘plant-microorganisms’ interactions. The composition of root exudates is therefore broad ranging, consisting of feeding, antimicrobial and signalling molecules. We thus focused this review on current research concerning the role of the root exudate composition in ‘plant-microorganisms’ interactions and functioning of the rhizosphere.Soil Biology and Biochemistry 10/2014; 77:69–80. DOI:10.1016/j.soilbio.2014.06.017 · 4.41 Impact Factor
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ABSTRACT: The significance of root exudates as belowground defense substances has long been underestimated, presumably due to being buried out of sight. Nevertheless, this chapter of root biology has been progressively addressed within the past decade through the characterization of novel constitutively secreted and inducible phytochemicals that directly repel, inhibit, or kill pathogenic microorganisms in the rhizosphere. In addition, the complex transport machinery involved in their export has been considerably unraveled. It has become evident that the profile of defense root exudates is not only diverse in its composition, but also strikingly dynamic. In this review, we discuss current knowledge of the nature and regulation of root-secreted defense compounds and the role of transport proteins in modulating their release.Trends in Plant Science 12/2013; 19(2). DOI:10.1016/j.tplants.2013.11.006 · 13.48 Impact Factor
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ABSTRACT: Corn (Zea mays) and Arabidopsis (Arabidopsis thaliana) produce GH family 19 plant class IV chitinases. These chitinases contain two domains: a small N-terminal hevein region, and a C-terminal chitinase. Numerous structures of GH19 chitinase domains have been reported, including the chitinase domain of corn ChitA. Structural information on the N-terminal domains, however, is lacking. Fusarium pathogens secrete fungalysin proteases that cleave some class IV chitinases at a well-defined Gly-Cys site between the two domains. To study the structure of the peptide domain we used the fungalysin protease Fv-cmp as a tool to release the hevein domain from plant class IV chitinases, allowing their direct study. MALDI-TOF MS analysis of fungalysin-released peptides from plant class IV chitinases from corn and Arabidopsis allowed visualization of multiple isotopomers, resulting in accurate mass determination. When treated with DTT, peptide ions increased in mass by six mass units, suggesting breakage of three disulfide bonds. When reduced peptides were S-alkylated, peptides were converted to a series of evenly spaced ions with various states of alkylation, confirming the presence of six reduced cysteines. This chemical data was complemented by use of molecular modeling to determine the fold of the peptide and location of disulfide bonds. The chemical data and molecular model combine to create a structural model of a hevein domain from a GH19 chitinase.Physiological and Molecular Plant Pathology 11/2014; 89. DOI:10.1016/j.pmpp.2014.11.004 · 1.99 Impact Factor