Auxin: regulation, action, and interaction.

Jasmonates: biosynthesis, perception, signal transduction and action in plant stress response, growth and development. An update to the 2007 review in Annals of Botany

Epigenetic phenomena in animals and plants are mediated by DNA methylation and stable chromatin modifications. There has been considerable interest in whether environmental factors modulate the establishment and maintenance of epigenetic modifications, and could thereby influence gene expression and phenotype. Chemical pollutants, dietary components, temperature changes and other external stresses can indeed have long-lasting effects on development, metabolism and health, sometimes even in subsequent generations. Although the underlying mechanisms remain largely unknown, particularly in humans, mechanistic insights are emerging from experimental model systems. These have implications for structuring future research and understanding disease and development.

Epigenetics and the environment: emerging patterns and implications.

EVidenceModeler (EVM) is presented as an automated eukaryotic gene structure annotation tool that reports eukaryotic gene structures as a weighted consensus of all available evidence. EVM, when combined with the Program to Assemble Spliced Alignments (PASA), yields a comprehensive, configurable annotation system that predicts protein-coding genes and alternatively spliced isoforms. Our experiments on both rice and human genome sequences demonstrate that EVM produces automated gene structure annotation approaching the quality of manual curation.

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Automated Eukaryotic Gene Structure Annotation Using EVidenceModeler and the Program to Assemble Spliced Alignments

■ Abstract Cytokinins are structurally diverse and biologically versatile. The chemistry and physiology of cytokinin have been studied extensively, but the regulation of cytokinin biosynthesis, metabolism, and signal transduction is still largely undefined. Recent advances in cloning metabolic genes and identifying putative receptors portend more rapid progress based on molecular techniques. This review centers on cytokinin metabolism with connecting discussions on biosynthesis and signal transduction. Important findings are summarized with emphasis on metabolic enzymes and genes. Based on the information generated to date, implications and future research directions are presented.

Cytokinin metabolism and action

The influence of cytokinins on ethylene production was examined using cotton leaf tissues. Treatment of intact cotton (Gossypium hirsutum L. cv LG 102) seedlings with both natural and synthetic cytokinins resulted in an increase in ethylene production by excised leaves. The effectiveness of the cytokinins tested was as follows: thidiazuron ≫ BA ≫ isopentyladenine ≥ zeatin ≫ kinetin. Using 100 micromolar thidiazuron (TDZ), an initial increase in ethylene production was observed 7 to 8 hours post-treatment, reached a maximum by 24 hours and then declined. Inhibitors of 1-aminocyclopropane-1-carboxylic acid (ACC) synthesis and its oxidation to ethylene reduced ethylene production 24 hours post-treatment; however, by 48 hours only inhibitors of ACC oxidation were effective. The increase in ethylene production was accompanied by a massive accumulation of ACC and its acid-labile conjugate. TDZ treatment resulted in a significant increase in the capacity of tissues to oxidize ACC to ethylene. Endogenous levels of methionine remained constant following TDZ treatment. It was concluded that the stimulation of ethylene production in cotton leaves following cytokinin treatment was the result of an increase in both the formation and oxidation of ACC.

Cytokinin-induced ethylene biosynthesis in nonsenescing cotton leaves.

The effects of post-harvest storage and dormancy progression on histone acetylation patterns were examined in potato (Solanum tuberosum L. cv. Russet Burbank) tubers. Storage of field-grown tubers at 3 degrees C in the dark resulted in the progressive loss of tuber meristem dormancy, defined as measurable growth after transfer to 20 degrees C for 7 days. Dormancy emergence was concomitant with sustained increases in histone H3.1 and H3.2 multi-acetylation, and with transient increases in H4 multi-acetylation that peaked 4-5 months post-harvest. Treatment of dormant tubers with bromoethane (BE) resulted in rapid loss of dormancy over 9 days. Similar to cold-stored field-grown tubers, dormancy break in BE-treated tubers occurred at the same time as transient rises in H4 and H3.1/3.2 multi-acetylation, peaking at days 1 and 4, respectively. BE treatment also resulted in small increases in RNA synthesis at day 6, and a three-fold, sustained activation of DNA synthesis thereafter. A defined sequence of epigenetic events, beginning with previously characterized transient cytosine demethylation, followed by increased H3 and H4 histone acetylation and ultimately, tuber meristem re-activation, may thus exist in potatoes during dormancy exit and resumption of rapid growth.

Changes in histone H3 and H4 multi-acetylation during natural and forced dormancy break in potato tubers.

Chromatin remodeling in plant cell culture: patterns of DNA methylation and histone H3 and H4 acetylation vary during growth of asynchronous potato cell suspensions.

Using an indirect enzyme-linked immunosorbent assay (ELISA), the effects of postharvest storage duration and temperature on endogenous cytokinins in potato (Solanum tuberosum L. cv. Russet Burbank) tuber apical bud tissues in relation to endodormancy status were determined. Following fractionation by HPLC, a total of eight cytokinins were detected and these were: zeatin riboside-5′-monophosphate (ZRMP), zeatin-O-glucoside (ZOG), zeatin (Z), zeatin riboside (ZR), isopentenyl adenosine-5′-monophosphate (IPMP), isopentenyl adenine-9-glucoside (IP-9-G), isopentenyl adenine (IP) and isopentenyl adenosine (IPA). Regardless of postharvest storage temperature or endodormancy status, IP-9-G was the most abundant cytokinin detected while ZRMP and ZOG were the least abundant ones. In tubers preincubated at a growth-permissive temperature (20°C) prior to extraction, the loss of endodormancy was preceded by significant increases in the endogenous levels of Z, ZR, IPMP and IP-9-G. When stored continuously at a growth-inhibiting temperature (3°C), significant increases in ZR, IP-9-G and IP + IPA were observed. The total content of cytokinins increased by over 7-fold during postharvest storage and this increase was a result of de novo biosynthesis. Dose-response studies using IPA and ZR demonstrated a time-dependent increase in apparent cytokinin sensitivity during postharvest storage. With the exception of IP-9-G, injection of any of these endogenous cytokinins resulted in the rapid and complete termination of tuber endodormancy. The significance of these results with respect to endodormancy regulation and the possible mechanisms controlling cytokinin levels in potato tubers are discussed.

Postharvest changes in endogenous cytokinins and cytokinin efficacy in potato tubers in relation to bud endodormancy

The plant hormone ethylene is involved in numerous plant processes including in vitro growth and regeneration. Manipulating ethylene in vitro may be useful for increasing plant regeneration from cultured cells. As part of ongoing efforts to improve plant regeneration from barley (Hordeum vulgare L.), we investigated ethylene emanation using our improved system and investigated methods of manipulating ethylene to increase regeneration. In vitro assays of regeneration from six cultivars, involving 10 weeks of callus initiation and proliferation followed by 8 weeks of plant regeneration, showed a correlation between regeneration and ethylene production: ethylene production was highest from 'Golden Promise', the best regenerator, and lowest from 'Morex' and 'DH-20', the poorest regenerators. Increasing ethylene production by addition of 1-aminocyclopropane 1-carboxylic acid (ACC) during weeks 8-10 increased regeneration from Morex. In contrast, adding ACC to Golden Promise cultures during any of the tissue culture steps reduced regeneration, suggesting that Golden Promise may produce more ethylene than needed for maximum regeneration rates. Blocking ethylene action with silver nitrate during weeks 5-10 almost doubled the regeneration from Morex and increased the Golden Promise regeneration 1.5-fold. Silver nitrate treatment of Golden Promise cultures during weeks 8-14 more than doubled the green plant regeneration. These results indicate that differential ethylene production is related to regeneration in the improved barley tissue culture system. Specific manipulations of ethylene were identified that can be used to increase the green plant regeneration from barley cultivars. The timing of ethylene action appears to be critical for maximum regeneration.

Jeffrey C. Suttle

Papers

Cytokinin-induced ethylene biosynthesis in nonsenescing cotton leaves.

Changes in histone H3 and H4 multi-acetylation during natural and forced dormancy break in potato tubers.

Chromatin remodeling in plant cell culture: patterns of DNA methylation and histone H3 and H4 acetylation vary during growth of asynchronous potato cell suspensions.

Postharvest changes in endogenous cytokinins and cytokinin efficacy in potato tubers in relation to bud endodormancy

Ethylene influences green plant regeneration from barley callus.