Proteomic analysis of dimorphic transition in the phytopathogenic fungus Ustilago maydis.

In the corn smut fungus Ustilago maydis, the dimorphic transition from budding to filamentous growth is intrinsically associated with the switch from a saprophytic to a pathogenic lifestyle. Both pathogenicity and filament formation are triggered by a heterodimeric homeodomain transcription factor encoded by the b mating type locus. Here, we present a reference map of the proteome of this dimorphic phytopathogenic fungus. Using 2-DE in combination with MALDI-TOF-MS and ESI-MS/MS, we were able to identify 250 distinct proteins obtained from soluble protein samples. In addition, we determined the abundance of cytosolic proteins in filamentous U. maydis cells and compared it with that of budding cells. Filamentous growth was induced by two independent regimes, either by overexpression of the bW2/bE1-heterodimer or by overexpression of the small GTP binding protein Rac1. By comparison of expression profiles, we have identified 13 protein spots that were significantly enhanced during filamentous growth induced by bW2/bE1. Rac1 only up-regulates a subset of four of these protein spots. None of these proteins have previously been associated with filamentous growth. Comparison of Rac1- and b-regulated protein sets supports the hypothesis that filament formation during pathogenic development occurs via stimulation of a Rac1-containing signalling module.

Desiccation of the resurrection plant Craterostigma plantagineum induces dynamic changes in protein phosphorylation.

Reversible phosphorylation of proteins is an important mechanism by which organisms regulate their reactions to external stimuli. To investigate the involvement of phosphorylation during acquisition of desiccation tolerance, we have analysed dehydration-induced protein phosphorylation in the desiccation tolerant resurrection plant Craterostigma plantagineum. Several dehydration-induced proteins were shown to be transiently phosphorylated during a dehydration and rehydration (RH) cycle. Two abundantly expressed phosphoproteins are the dehydration- and abscisic acid (ABA)-responsive protein CDeT11-24 and the group 2 late embryogenesis abundant (LEA) protein CDeT6-19. Although both proteins accumulate in leaves and roots with similar kinetics in response to dehydration, their phosphorylation patterns differ. Several phosphorylation sites were identified on the CDeT11-24 protein using liquid chromatography-tandem mass spectrometry (LCMS/MS). The coincidence of phosphorylation sites with predicted coiled-coil regions leads to the hypothesis that CDeT11-24 phosphorylations influence the stability of coiled-coil interactions with itself and possibly other proteins.

A homeodomain leucine zipper gene from Craterostigma plantagineum regulates abscisic acid responsive gene expression and physiological responses.

A subset of homeodomain leucine zipper proteins (HDZip) play a role in regulating adaptation responses including developmental adjustment to environmental cues in plants. Here we report the structural and functional characterisation of a dehydration responsive nuclear-targeted HDZip transcriptional regulator, CpHB-7. DNA-protein interaction studies suggest that CDeT6-19, a known ABA and dehydration responsive dehydrin gene, is a potential target gene of CpHB-7 in the desiccation-tolerant plant Craterostigma plantagineum. Transgenic plants that ectopically express CpHB-7 display reduced sensitivity towards ABA during seed germination and stomatal closure. Expression analysis reveals that genes with induced or repressed expression in CpHB-7 ectopic expression lines are either mostly repressed or induced by ABA, drought or salt treatment respectively, thus demonstrating that CpHB-7 modifies ABA-responsive gene expression as a negative regulator. CpHB-7 gene expression is also linked to early organ development, leading to the suggestion that CpHB-7 is functionally similar to the Arabidopsis transcription factor, ATHB-6.

A reference map of the Arabidopsis thaliana mature pollen proteome.

The male gametophyte (or pollen) plays an obligatory role during sexual reproduction of higher plants. The extremely reduced complexity of this organ renders pollen a valuable experimental system for studying fundamental aspects of plant biology such as cell fate determination, cell-cell interactions, cell polarity, and tip-growth. Here, we present the first reference map of the mature pollen proteome of the dicotyledonous model plant species, Arabidopsis thaliana. Based on two-dimensional gel electrophoresis, matrix-assisted laser desorption/ionization time-of-flight, and electrospray quadrupole time-of-flight mass spectrometry, we reproducibly identified 121 different proteins in 145 individual spots. The presence, subcellular localization, and functional classification of the identified proteins are discussed in relation to the pollen transcriptome and the full protein complement encoded by the nuclear Arabidopsis genome.