Buds are specialized structures that protect fragile meristematic regions during dormancy and are part of the mechanism that plants use to survive unfavorable environmental conditions such as low temperature or dessication stress. The evergrowing (evg) mutant of peach [Prunus persica (L.) Batsch] does not form terminal vegetative buds in response to dormancy-inducing conditions such as short days and low temperatures, and the terminal meristems maintain constant growth (leaf addition and internode elongation). We genetically mapped the evg trait and identified the corresponding genomic region in a wild-type genome. We sequenced and annotated the 132-kb region. Nineteen genes were predicted to be in the sequenced region. Ten of the predicted genes were demonstrated to be expressed in the wild-type germplasm but six of these were not expressed in mutant tissues. These six genes are a cluster of MIKC-type MADS-box transcription factors similar to genes from Ipomoea batatas and Solanum tuberosum MADS-box, which also regulate meristem growth in vegetative tissues. A 41,746-bp deletion is present in this region of the mutant genome which results in the loss of all or part of four of the six MADS-box genes. The six MADS-box genes that are not expressed in the mutant are candidates for the regulation of growth cessation and terminal bud formation in peach in response to dormancy-inducing conditions and have been named dormancy-associated MADS-box (DAM) genes.

SUMMARYTrees are capable of tremendous architectural plasticity, allowing them to maximize their light exposure under highly competitive environments. One key component of tree architecture is the branch angle, yet little is known about the molecular basis for the spatial patterning of branches in trees. Here, we report the identification of a candidate gene for the br mutation in Prunus persica (peach) associated with vertically oriented growth of branches, referred to as 'pillar' or 'broomy'. Ppa010082, annotated as hypothetical protein in the peach genome sequence, was identified as a candidate gene for br using a next generation sequence-based mapping approach. Sequence similarity searches identified rice TAC1 (tiller angle control 1) as a putative ortholog, and we thus named it PpeTAC1. In monocots, TAC1 is known to lead to less compact growth by increasing the tiller angle. In Arabidopsis, an attac1 mutant showed more vertical branch growth angles, suggesting that the gene functions universally to promote the horizontal growth of branches. TAC1 genes belong to a gene family (here named IGT for a shared conserved motif) found in all plant genomes, consisting of two clades: one containing TAC1-like genes; the other containing LAZY1, which contains an EAR motif, and promotes vertical shoot growth in Oryza sativa (rice) and Arabidopsis through influencing polar auxin transport. The data suggest that IGT genes are ancient, and play conserved roles in determining shoot growth angles in plants. Understanding how IGT genes modulate branch angles will provide insights into how different architectural growth habits evolved in terrestrial plants.

Seasonal patterns of proteins and of cold hardiness were characterized in bark and xylem tissues of genetically related (sibling) deciduous and evergreen peach (Prunus persica [L.] Batsch). In contrast with deciduous trees, which entered endodormancy and abscised leaves in the fall, evergreen trees retained their leaves and exhibited shoot elongation under favorable environmental conditions. A successive increase in the cold hardiness of bark and xylem was observed during the fall in both genotypes. This was followed by a subsequent decrease from midwinter to spring. Xylem tissue in both genotypes exhibited deep supercooling and a significant correlation (r = 0.99) between the midpoint of the lowtemperature exotherm and the subzero temperature at which 50% injury occurred (assessed by electrolyte leakage) was noted. The maximum hardiness level attained in deciduous trees was more than twofold that of evergreens. Seasonal pattern of proteins from bark and xylem of the sibling genotypes was characterized by onedimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Among other qualitative and quantitative changes, accumulation of a 19-kilodalton polypeptide in the bark of both genotypes was observed during fall followed by a decrease in spring. This polypeptide accumulated to higher levels in the deciduous peach compared with the evergreen. Additionally, a 16-kilodalton protein exhibited the same pattern in deciduous trees but not in the evergreen trees. Both the 19-and a 16-kilodalton bark proteins conform to the criteria of a bark storage protein. Empress dwarf. Subsequently, OP seed was collected from the F1 tree of Empress dwarf OP x evergreen P.I. 442380. Assuming that most OP seed resulted from selfing (8), the seeds were planted and the growth characteristics of individual trees were evaluated over several years. Of relevance to the present study, approximately 25% of the trees from the F2 generation exhibited a deciduous habit and a period of endodormancy typical of temperate fruit trees, whereas another 25% of the trees exhibited an evergreen habit with continuous terminal growth under favorable environmental conditions and other features indicative of a lack of endodormancy. The remaining 50% of the trees were presumed to be heterozygotes, which were characterized by late leaf abscission in the fall (R. Scorza, personal communication).Cold acclimation in deciduous, woody perennials, including fruit trees, is a seasonal process that is marked by an increased cold tolerance in fall, reaching maximum in winter (cold acclimation), followed by a decrease in tolerance during spring, and reaching the minimum in summer (deacclimation) (18). Overwintering deciduous trees also enter into endodormancy during the same time as they develop cold hardiness. Early studies on the seasonal variation in protein content of cortical bark cells of black locust (Robinia pseudoacacia) demonstrated the accumulation of soluble proteins in the fall with a parallel increase in freezing tolerance. This was fol...

BackgroundLignification of the fruit endocarp layer occurs in many angiosperms and plays a critical role in seed protection and dispersal. This process has been extensively studied with relationship to pod shatter or dehiscence in Arabidopsis. Dehiscence is controlled by a set of transcription factors that define the fruit tissue layers and whether or not they lignify. In contrast, relatively little is known about similar processes in other plants such as stone fruits which contain an extremely hard lignified endocarp or stone surrounding a single seed.ResultsHere we show that lignin deposition in peach initiates near the blossom end within the endocarp layer and proceeds in a distinct spatial-temporal pattern. Microarray studies using a developmental series from young fruits identified a sharp and transient induction of phenylpropanoid, lignin and flavonoid pathway genes concurrent with lignification and subsequent stone hardening. Quantitative polymerase chain reaction studies revealed that specific phenylpropanoid (phenylalanine ammonia-lyase and cinnamate 4-hydroxylase) and lignin (caffeoyl-CoA O-methyltransferase, peroxidase and laccase) pathway genes were induced in the endocarp layer over a 10 day time period, while two lignin genes (p-coumarate 3-hydroxylase and cinnamoyl CoA reductase) were co-regulated with flavonoid pathway genes (chalcone synthase, dihydroflavanol 4-reductase, leucoanthocyanidin dioxygen-ase and flavanone-3-hydrosylase) which were mesocarp and exocarp specific. Analysis of other fruit development expression studies revealed that flavonoid pathway induction is conserved in the related Rosaceae species apple while lignin pathway induction is not. The transcription factor expression of peach genes homologous to known endocarp determinant genes in Arabidopsis including SHATTERPROOF, SEEDSTCK and NAC SECONDARY WALL THICENING PROMOTING FACTOR 1 were found to be specifically expressed in the endocarp while the negative regulator FRUITFUL predominated in exocarp and mesocarp.ConclusionsCollectively, the data suggests, first, that the process of endocarp determination and differentiation in peach and Arabidopsis share common regulators and, secondly, reveals a previously unknown coordination of competing lignin and flavonoid biosynthetic pathways during early fruit development.

Plum hypocotyl slices were transformed with the coat protein (CP) gene of plum pox virus (PPV-CP) following cocultivation with Agrobacterium tumefaciens containing the plasmid pGA482GG/PPVCP-33. This binary vector carries the PPV-CP gene construct, as well as the chimeric neomycin phosphotransferase and β-glucuronidase genes. Integration and expression of the transferred genes into regenerated plum plants was verified through kan resistance, GUS assays, and PCR amplification of the PPV-CP gene. Twenty-two transgenic clones were identified from approximately 1800 hypocotyl slices. DNA, mRNA, and protein analyses of five transgenic plants confirmed the integration of the engineered CP gene, the accumulation of CP mRNA and of PPV-CP-immunoreactive protein. CP mRNA levels ranged from high to undetectable levels, apparently correlated with gene structure, as indicated by DNA blot analysis. Western analysis showed that transgenic plants produced amounts of CP which generally correlated with amounts of detected mRNA.

Volatile fractions were prepared from four ripe commercial peach cultivars and two breeding lines by continuous vacuum steam distillation-hexane extraction and analyzed by capillary gas-liquid chromatography and gas-liquid chromatography/mass spectrometry. Thirty-three compounds were identified including five C, aldehydes and alcohols, six lactones, five monoterpenes, one sesquiterpene, one ester, three high molecular weight hydrocarbons (C,,, CZ3, C,,), and twelve other compounds.Major compounds identified were hexanal, (E)-a-hexenal, benzaldehyde, linalool, 6-pentyl-a-pyrone, y-and &decalactones, hexadecanoic acid, and three saturated hydrocarbons. By the use of threshold values and concentrations, odor units were calculated for the major low and medium molecular weight compounds to determine their contribution to peach aroma. Variations in the volatile constituents during maturation were also determined for two peach cultivars. Concentrations of most compounds increased with maturity of fruit. (E)-2-Hexenal increased in Cresthaven peaches but decreased in Monroe. Hexanal showed erratic behavior, increasing in Cresthaven and decreasing in Monroe.Many of the biochemical changes occurring during fruit ripening relate indirectly to quality. Quality was defined by Kramer and Twigg (1966) as the composite of those chemical and physical characteristics that make a product possess consumer appeal and acceptability. One of the most important aspects of these characteristics is fruit flavor.Several investigations on peach flavor have resulted in the identification of approximately 70 volatile compounds. Lactones have been implicated in peach aroma with informal sensory judgments by Jennings and Sevenants (1964), Jennings (1966,1971), Broderick (1966, 1975), and Do et al. (1969. Lim (1963), Lim and Romani (1964), and Do e t al. (1969) investigated volatile compounds from peaches at different maturity stages and during artificial ripening. Spencer et al. (1978) reported on the relationship between sensory characteristics and relative concentration of the volatile compounds of fresh and cooked peaches. Among the 10 peach varieties investigated, the major differences found were higher concentrations of esters and monoterpenes relative to lactones. However, she reported that the lactones made the major contribution to the "peachy" aroma.The present investigation was conducted to identify and quantitate the volatile constituents in peach cultivars by gas-liquid chromatography a n d gas-liquid chromatography/mass spectrometry. Also, the relative contributions of low and medium molecular weight compounds to peach aroma were evaluated.Variations in the volatile constituents during maturation for two peach cultivars were also determined. EXPERIMENTAL SECTIONMaterials. Tree-ripened peaches were obtained from the Appalachian Fruit Research Station, USDA-ARS, Kearneysville, WV, from the University of Georgia Horticultural Farm, Athens, GA, and from nearby commercial orchards. Fruits were analyzed within 24 h after harvest. Immedia...

Gain-of-function studies have shown that ectopic expression of the BABY BOOM (BBM) AP2/ ERF domain transcription factor is suYcient to induce spontaneous somatic embryogenesis in Arabidopsis (Arabidopsis thaliana (L.) Heynh) and Brassica napus (B. napus L.) seedlings. Here we examined the eVect of ectopic BBM expression on the development and regenerative capacity of tobacco (Nicotiana tabacum L.) through heterologous expression of Arabidopsis and B. napus BBM genes. 35S::BBM tobacco lines exhibited a number of the phenotypes previously observed in 35S::BBM Arabidopsis and B. napus transgenics, including callus formation, leaf rumpling, and sterility, but they did not undergo spontaneous somatic embryogenesis. 35S::BBM plants with severe ectopic expression phenotypes could not be assessed for enhanced regeneration at the seedling stage due to complete male and female sterility of the primary transformants, therefore fertile BBM ectopic expression lines with strong misexpression phenotypes were generated by expressing a steroid-inducible, posttranslationally controlled BBM fusion protein (BBM:GR) under the control of a 35S promoter. These lines exhibited spontaneous shoot and root formation, while somatic embryogenesis could be induced from in-vitro germinated seedling hypocotyls cultured on media supplemented with cytokinin. Together these results suggest that ectopic BBM expression in transgenic tobacco also activates cell proliferation pathways, but diVerences exist between Arabidopsis/B. napus and N. tabacum with respect to their competence to respond to the BBM signalling molecule.

Evergrowing (EVG) peach is one of only two described mutants affecting winter dormancy in woody perennial species. EVG peach does not set terminal buds, cease new leaf growth, nor enter into a dormant resting phase in response to winter conditions. The EVG mutation segregates in F2 progeny as a single recessive nuclear gene. A local molecular genetic linkage map around EVG was previously developed using amplified fragment length polymorphism (AFLP) and simple sequence repeat (SSR) markers, and a bacterial artificial chromosome (BAC) contig that contains the EVG mutation was assembled. A MADS box coding open reading frame (ORF) was found in a BAC of this contig and used as a probe. The probe detected a polymorphism between the wild-type and mutant genomes, and the polymorphism is indicative of a deletion in EVG peach. The EVG gene region contained six potential MADS-box transcription factor sequences, and the deletion in EVG affected at least four of these. The deletion was bracketed using RFLP analysis, which showed that it is contained within a segment of the genome no greater than 180 kb.