Two highly divergent alcohol dehydrogenases of melon exhibit fruit ripening-specific expression and distinct biochemical characteristics

Alcohol dehydrogenases (ADH) participate in the biosynthetic pathway of aroma volatiles in fruit by interconverting aldehydes to alcohols and providing substrates for the formation of esters. Two highly divergent ADH genes (15% identity at the amino acid level) of Cantaloupe Charentais melon (Cucumis melo var. Cantalupensis) have been isolated. Cm-ADH1 belongs to the medium-chain zinc-binding type of ADHs and is highly similar to all ADH genes expressed in fruit isolated so far. Cm-ADH2 belongs to the short-chain type of ADHs. The two encoded proteins are enzymatically active upon expression in yeast. Cm-ADH1 has strong preference for NAPDH as a co-factor, whereas Cm-ADH2 preferentially uses NADH. Both Cm-ADH proteins are much more active as reductases with Kms 10–20 times lower for the conversion of aldehydes to alcohols than for the dehydrogenation of alcohols to aldehydes. They both show strong preference for aliphatic aldehydes but Cm-ADH1 is capable of reducing branched aldehydes such as 3-methylbutyraldehyde, whereas Cm-ADH2 cannot. Both Cm-ADH genes are expressed specifically in fruit and up-regulated during ripening. Gene expression as well as total ADH activity are strongly inhibited in antisense ACC oxidase melons and in melon fruit treated with the ethylene antagonist 1-methylcyclopropene (1-MCP), indicating a positive regulation by ethylene. These data suggest that each of the Cm-ADH protein plays a specific role in the regulation of aroma biosynthesis in melon fruit

Expression and trans-specific polymorphism of self-incompatibility RNases in Coffea (Rubiaceae)

Self-incompatibility (SI) is widespread in the angiosperms, but identifying the biochemical components of SI mechanisms has proven to be difficult in most lineages. Coffea (coffee; Rubiaceae) is a genus of old-world tropical understory trees in which the vast majority of diploid species utilize a mechanism of gametophytic self-incompatibility (GSI). The S-RNase GSI system was one of the first SI mechanisms to be biochemically characterized, and likely represents the ancestral Eudicot condition as evidenced by its functional characterization in both asterid (Solanaceae, Plantaginaceae) and rosid (Rosaceae) lineages. The S-RNase GSI mechanism employs the activity of class III RNase T2 proteins to terminate the growth of "self" pollen tubes. Here, we investigate the mechanism of Coffea GSI and specifically examine the potential for homology to S-RNase GSI by sequencing class III RNase T2 genes in populations of 14 African and Madagascan Coffea species and the closely related self-compatible species Psilanthus ebracteolatus. Phylogenetic analyses of these sequences aligned to a diverse sample of plant RNase T2 genes show that the Coffea genome contains at least three class III RNase T2 genes. Patterns of tissue-specific gene expression identify one of these RNase T2 genes as the putative Coffea S-RNase gene. We show that populations of SI Coffea are remarkably polymorphic for putative S-RNase alleles, and exhibit a persistent pattern of trans-specific polymorphism characteristic of all S-RNase genes previously isolated from GSI Eudicot lineages. We thus conclude that Coffea GSI is most likely homologous to the classic Eudicot S-RNase system, which was retained since the divergence of the Rubiaceae lineage from an ancient SI Eudicot ancestor, nearly 90 million years ago.United States National Science Foundation [0849186]; Society of Systematic Biologists; American Society of Plant Taxonomists; Duke University Graduate Schoolinfo:eu-repo/semantics/publishedVersio

Histone deacetylase HD2 interacts with ERF1 and is involved in longan fruit senescence

Histone deacetylation plays an important role in epigenetic control of gene expression. HD2 is a plant-specific histone deacetylase that is able to mediate transcriptional repression in many biological processes. To investigate the epigenetic and transcriptional mechanisms of longan fruit senescence, one histone deacetylase 2-like gene, DlHD2, and two ethylene-responsive factor-like genes, DlERF1 and DlERF2, were cloned and characterized from longan fruit. Expression of these genes was examined during fruit senescence under different storage conditions. The accumulation of DlHD2 reached a peak at 2 d and 30 d in the fruit stored at 25 °C (room temperature) and 4 °C (low temperature), respectively, or 6 h after the fruit was transferred from 4 °C to 25 °C, when fruit senescence was initiated. However, the DlERF1 transcript accumulated mostly at the later stage of fruit senescence, reaching a peak at 5 d and 35 d in the fruit stored at 25 °C and 4 °C, respectively, or 36 h after the fruit was transferred from low temperature to room temperature. Moreover, application of nitric oxide (NO) delayed fruit senescence, enhanced the expression of DlHD2, but suppressed the expression of DlERF1 and DlERF2. These results indicated a possible interaction between DlHD2 and DlERFs in regulating longan fruit senescence, and the direct interaction between DlHD2 and DlERF1 was confirmed by yeast two-hybrid and bimolecular fluorescence complementation (BiFC) assays. Taken together, the results suggested that DlHD2 may act with DlERF1 to regulate gene expression involved in longan fruit senescence

Cytological events induced by arachidonic acid in potato tubers

Necrosis of potato tuber cells is enhanced, after 24 h incubation, by arachidonic acid (AA), an elicitor of the hypersensitive response in Solanum tuberosum L. and also by Fenton's reagents (a hydroxyl radical-generating system) either alone or in association with AA. The phenomenon is independent of tuber age. In aged tubers, phenylthiourea (PTU) causes a significant reduction of AA-induced cell necrosis. Necrosis observed in the presence of PTU alone is lower than in other treatments, and neither different from the controls nor affected by tuber age. Cell size is not affected by treatments or ageing. Nuclear hypertrophy occurs independently of tuber age, with the highest values after treatment with AA and Fenton's reagents. Nucleolar extrusion is observed in all treatments but earliest in the presence of AA. AA also enhances the number of lignified parenchymal cells and, to a lesser extent, the number of tracheary elements