Molecular identification of 1-Cys peroxiredoxin and anthocyanidin/flavonol 3-O-galactosyltransferase from proanthocyanidin-rich young fruits of persimmon (Diospyros kaki Thunb.)

Fruits of persimmon (Diospyros kaki Thunb.) accumulate large amounts of proanthocyanidins (PAs) in the early stages of development. Astringent (A)-type fruits remain rich in soluble PAs even after they reach full-mature stage, whereas non-astringent (NA)-type fruits lose these compounds before full maturation. As a first step to elucidate the mechanism of PA accumulation in this non-model species, we used suppression subtractive hybridization to identify transcripts accumulating differently in young fruits of A- and NA-type. Interestingly, only a few clones involved in PA biosynthesis were identified in A–NA libraries. Represented by multiple clones were those encoding a novel 1-Cys peroxiredoxin and a new member of family 1 glycosyltransferases. Quantitative RT-PCR analyses confirmed correlation of the amount of PAs and accumulation of transcripts encoding these proteins in young persimmon fruits. Furthermore, the new family 1 glycosyltransferase was produced in Escherichia coli and shown to efficiently catalyze galactosylation at 3-hydroxyl groups of several anthocyanidins and flavonols. These findings suggest a complex mechanism of PA accumulation in persimmon fruits

Differential regulation of the barley (Hordeum vulgare) transcripts B22E and B12D in mature aleurone layers

Previously, B12D and B22E have been characterized as Barley aleurone and embryo (Balem) transcripts, expressed during seed maturation and embryo germination. The open reading frame of B12D cDNAs encodes a protein of unknown function highly conserved in mono-and dicotyledonous species, while B22E encodes a metallothionein-like protein. Several slightly different B22E transcripts have earlier been identified. Our objective was to investigate the number of B12D genes, and B12D and B22E expression patterns in mature aleurone. Gnomic Southern hybridization and primer extension experiments suggest the presence of a B12D gene family in barley with at least 8 or 9 members. B12D transcripts can also be identified in the starchy endosperm, and a primer extension analysis indicates that some of these genes are expressed in the starchy endosperm only. A number of genes appear to be transcribed in all tissues investigated; starchy endosperm, pericarp, immature and mature embryos and aleurone, and mature aleurone incubated with GA(3). One B12D gene, HvB12Dg1, was isolated and shown by particle bombardment with a promoter-GUS construct to be transcriptionally active. The HvR12Dg1 promoter contains elements similar to those of the gibberellic acid response complex (GARC). B12D transcripts are found in the aleurone of imbibed embryoless grains, while B22E transcripts are barely detectable. However, both transcripts are up-regulated by the presence of the germinating embryo. For B22E this effect is not mimicked by applying GA(3) exogenously to imbibed embryoless grains, while the B12D transcript level increases 2- to 3-fold, at most. On the other hand, ABA can suppress B12D expression. Our investigations indicate that gibberellic acid may not be directly involved in the up-regulation of all transcripts induced in the aleurone during germination

A peroxiredoxin antioxidant is encoded by a dormancy-related gene, Per1, expressed during late development in the aleurone and embryo of barley grains

Antioxidants can remove damaging reactive oxygen species produced as by-products of desiccation and respiration during late embryogenesis, imbibition of dormant seeds and germination. We have expressed a protein, PER1, encoded by the Balem (barley aleurone and embryo) transcript previously called B15C, and show it to reduce oxidative damage in vitro. PER1 shares high similarity to a novel group of thiol-requiring antioxidants, named peroxiredoxins, and represents a subgroup with only one conserved cysteine residue (l-Cys). PER1 is the first antioxidant belonging to the l-Cys subgroup shown to be functionally active, and the first peroxiredoxin of any kind to be functionally described in plants. The steady state level of the transcript, Per1, homologous to a dormancy-related transcript (pBS128) from bromegrass (Bromus secalinus), increases considerably in imbibed embryos from dormant barley (Hordeum vulgare L.) grains. Our investigations also indicate that Per1 transcript levels are dormancy-related in the aleurone layer of whole grains. In contrast to most seed-expressed antioxidants Per1 disappears in germinating embryos, and in the mature aleurone the transcript is down-regulated by the germinating embryo or by gibberellic acid (GA). Our data show that the barley seed peroxiredoxin is encoded by a single Per1 gene. Possible roles of the PER1 peroxiredoxin in barley grains during desiccation, dormancy and imbibition are discussed

Functional characterisation of the peroxiredoxin gene family members of Synechococcus elongatus PCC 7942

Stork T, Laxa M, Dietz MS, Dietz K-J. Functional characterisation of the peroxiredoxin gene family members of Synechococcus elongatus PCC 7942. ARCHIVES OF MICROBIOLOGY. 2009;191(2):141-151.The genome of Synechococcus elongatus PCC 7942 encodes six peroxiredoxins (Prx). Single genes are present each for a 1-Cys Prx and a 2-Cys Prx, while four genes code for PrxQ-like proteins (prxQ-A1, -A2, -A3 and B). Their transcript accumulation varies with growth conditions in a gene-specific manner (Stork et al. in J Exp Bot 56:3193-3206, 2005). To address their functional properties, members of the prx gene family were produced as recombinant proteins and analysed for their peroxide detoxification capacity and quaternary structure by size exclusion chromatography. Independent of the reduction state, the 2-Cys Prx separated as oligomer, the 1-Cys Prx as dimer and the PrxQ-A1 as monomer. PrxQ-A2 was inactive in our assays, 1-Cys Prx activity was unaffected by addition of TrxA, while all others were stimulated to a variable extent by addition of E. coli thioredoxin. Sensitivity towards cumene hydroperoxide treatment of E. coli BL21 cells expressing the cyanobacterial PrxQ-A1 to A3 proteins was greatly reduced, while expression of the other Prx had no effect. The study shows differentiation of Prx functions in S. elongatus PCC 7942 which is discussed in relation to potential roles in site- and stress-specific defence