http://www.plantphysiol.org PLANT PHYSIOLOGY RSS feed -- recent GENETICS, GENOMICS, AND MOLECULAR EVOLUTION articles 1532-2548 PLANT PHYSIOLOGY 0032-0889 http://www.plantphysiol.org/icons/banner/title.gif http://www.plantphysiol.org http://www.plantphysiol.org/cgi/content/short/151/3/1658?rss=1 Members of the conserved RecQ helicase family are important for the preservation of genomic stability. Multiple RecQ homologs within one organism raise the question of functional specialization. Whereas five different homologs are present in humans, the model plant Arabidopsis (Arabidopsis thaliana) carries seven RecQ homologs in its genome. We performed biochemical analysis of AtRECQ3, expanded upon a previous analysis of AtRECQ2, and compared their properties. Both proteins differ in their domain composition. Our analysis demonstrates that they are 3' to 5' helicases with similar activities on partial duplex DNA. However, they promote different outcomes with synthetic DNA structures that mimic Holliday junctions or a replication fork. AtRECQ2 catalyzes Holliday junction branch migration and replication fork regression, while AtRECQ3 cannot act on intact Holliday junctions. The observed reaction of AtRECQ3 on the replication fork is in line with unwinding the lagging strand. On nicked Holliday junctions, which have not been intensively studied with RecQ helicases before, AtRECQ3, but not AtRECQ2, shows a clear preference for one unwinding mechanism. In addition, AtRECQ3 is much more efficient at catalyzing DNA strand annealing. Thus, AtRECQ2 and AtRECQ3 are likely to perform different tasks in the cell, and AtRECQ3 differs in its biochemical properties from all other eukaryotic RECQ helicases characterized so far.

]]> Tue, 03 Nov 2009 12:22:28 PST info:doi/10.1104/pp.109.144709 American Society of Plant Biologists 3 151 1666 2009-11-01 1658 GENETICS, GENOMICS, AND MOLECULAR EVOLUTION http://www.plantphysiol.org/cgi/content/short/151/2/782?rss=1 The conquest of the land by plants required dramatic morphological and metabolic adaptations. Complex developmental programs under tight regulation evolved during this process. Key regulators of plant development are phytohormones, such as cytokinins. Cytokinins are adenine derivatives that affect various processes in plants. The cytokinin signal transduction system, which is mediated via a multistep variant of the bacterial two-component signaling system, is well characterized in the model plant Arabidopsis (Arabidopsis thaliana). To understand the origin and evolutionary pattern of this signaling pathway, we surveyed the genomes of several sequenced key plant species ranging from unicellular algae, moss, and lycophytes, to higher land plants, including Arabidopsis and rice (Oryza sativa), for proteins involved in cytokinin signal transduction. Phylogenetic analysis revealed that the hormone-binding receptor and a class of negative regulators first appeared in land plants. Other components of the signaling pathway were present in all species investigated. Furthermore, we found that the receptors evolved under different evolutionary constraints from the other components of the pathway: The number of receptors remained fairly constant, while the other protein families expanded.

]]> Thu, 01 Oct 2009 06:20:41 PDT info:doi/10.1104/pp.109.139188 American Society of Plant Biologists 2 151 791 2009-10-01 782 GENETICS, GENOMICS, AND MOLECULAR EVOLUTION