AtERF#111/ABR1 is a transcriptional activator involved in the wounding response.

AtERF#111/ABR1 belongs to the group X of the ERF/AP2 transcription factor family (GXERFs) and is shoot specifically induced under submergence and hypoxia. It was described to be an ABA-response repressor, but our data reveal a completely different function. Surprisingly, AtERF#111 expression is strongly responsive to wounding stress. Expression profiling of ERF#111-overexpressing (OE) plants, which show morphological phenotypes like increased root hair length and number, strengthens the hypothesis of AtERF#111 being involved in the wounding response, thereby acting as a transcriptional activator of gene expression. Consistent with a potential function outside of oxygen signalling, we could not assign AtERF#111 as a target of the PRT6 N-degron pathway, even though it starts with a highly conserved N-terminal Met-Cys (MC) motif. However, the protein is unstable as it is degraded in an ubiquitin-dependent manner. Finally, direct target genes of AtERF#111 were identified by microarray analyses and subsequently confirmed by protoplast transactivation assays. The special roles of diverse members of the plant-specific GXERFs in coordinating stress signalling and wound repair mechanisms have been recently hypothesized, and our data suggest that AtERF#111 is indeed involved in these processes.

Dirigent proteins in plants: modulating cell wall metabolism during abiotic and biotic stress exposure.

Dirigent (DIR) proteins were found to mediate regio- and stereoselectivity of bimolecular phenoxy radical coupling during lignan biosynthesis. Here we summarize the current knowledge of the importance of DIR proteins in lignan and lignin biosynthesis and highlight their possible importance in plant development. We focus on the still rather enigmatic Arabidopsis DIR gene family, discussing the few members with known functional importance. We comment on recent discoveries describing the detailed structure of two DIR proteins with implications in the mechanism of DIR-mediated catalysis. Further, we summarize the ample evidence for stress-induced dirigent gene expression, suggesting the role of DIRs in adaptive responses. In the second part of our work, we present a preliminary bioinformatics-based characterization of the AtDIR family. The phylogenetic analysis of AtDIRs complemented by comparison with DIR proteins of mostly known function from other species allowed us to suggest possible roles for several members of this family and identify interesting AtDIR targets for further study. Finally, based on the available metadata and our in silico analysis of AtDIR promoters, we hypothesize about the existence of specific transcriptional controls for individual AtDIR genes and implicate them in various stress responses, hormonal regulations, and developmental processes.

The greening after extended darkness1 is an N-end rule pathway mutant with high tolerance to submergence and starvation.

Plants respond to reductions in internal oxygen concentrations with adaptive mechanisms (for example, modifications of metabolism to cope with reduced supply of ATP). These responses are, at the transcriptional level, mediated by the group VII Ethylene Response Factor transcription factors, which have stability that is regulated by the N-end rule pathway of protein degradation. N-end rule pathway mutants are characterized by a constitutive expression of hypoxia response genes and abscisic acid hypersensitivity. Here, we identify a novel proteolysis6 (prt6) mutant allele, named greening after extended darkness1 (ged1), which was previously discovered in a screen for genomes uncoupled-like mutants and shows the ability to withstand long periods of darkness at the seedling stage. Interestingly, this ethyl methanesulfonate-derived mutant shows unusual chromosomal rearrangement instead of a point mutation. Furthermore, the sensitivity of N-end rule pathway mutants ged1 and prt6-1 to submergence was studied in more detail to understand previously contradicting experiments on this topic. Finally, it was shown that mutants for the N-end rule pathway are generally more tolerant to starvation conditions, such as prolonged darkness or submergence, which was partially associated with carbohydrate conservation.