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The effect of different chilling and gibberellin treatments on growth and development of the peach rootstocks 'Nemaguard' and 'GF305' was studied. A factorial experiment was designed combining cold treatments (0, 5, 15 and 30 days at 4°C temperature) and GA3 concentrations (0, 100 and 200 mg/L). The variables considered were: percentage of germination, number of internodes, plant height and the ratio plant height/number of internodes. Results showed an overall growth increase as a consequence of chilling and gibberellin addition; however the behaviour of the two assayed rootstocks was slightly different. In general terms, 'Nemaguard' responded well to 5 days cold and chilling treatments did not improve growth in a relevant way, whereas 'GF305' showed a more gradual effect of the chilling and gibberellin treatments on the studied parameters. © ISHS 2012.

Release of bud dormancy in perennial plants resembles vernalization in Arabidopsis thaliana and cereals. In both cases a certain period of chilling is required for accomplishing the reproductive phase, and several transcription factors with the MADS-box domain perform a central regulatory role in these processes. The expression of DORMANCY ASSOCIATED MADS-box (DAM)-related genes has been found to be up-regulated in dormant buds of numerous plant species such as poplar, raspberry, leafy spurge, blackcurrant, Japanese apricot and peach. Moreover, functional evidence suggests the involvement of DAM genes in the regulation of seasonal dormancy in peach. Recent findings highlight the presence of genome-wide epigenetic modifications related to dormancy events, and more specifically the epigenetic regulation of DAM-related genes in a similar way to FLOWERING LOCUS C (FLC), a key integrator of vernalization effectors on flowering initiation in Arabidopsis. We revise the most relevant molecular and genomic contributions in the field of bud dormancy, and discuss the increasing evidence for chromatin modifications involvement in the epigenetic regulation of seasonal dormancy cycles in perennial plants.

Reproductive meristems and embryos display dormancy mechanisms in specialized structures named respectively buds and seeds that arrest the growth of perennial plants until environmental conditions are optimal for survival. Dormancy shows common physiological features in buds and seeds. A genotype-specific period of chilling is usually required to release dormancy by molecular mechanisms that are still poorly understood. In order to find common transcriptional pathways associated to dormancy release, we analyzed the chilling-dependent expression in embryos of certain genes that were previously found related to dormancy in flower buds of peach. We propose the presence of short and long-term dormancy events affecting respectively the germination rate and seedling development by independent mechanisms. Short periods of chilling seem to improve germination in an abscisic acid-dependent manner, whereas the positive effect of longer cold treatments on physiological dwarfing coincides with the accumulation of phenylpropanoids in the seed

• Bud dormancy release in many woody perennial plants responds to the seasonal accumulation of chilling stimulus. MADS-box transcription factors encoded by DORMANCY ASSOCIATED MADS-box (DAM) genes in peach (Prunus persica) are implicated in this pathway, but other regulatory factors remain to be identified. In addition, the regulation of DAM gene expression is not well known at the molecular level. • A microarray hybridization approach was performed to identify genes whose expression correlates with the bud dormancy-related behaviour in 10 different peach cultivars. Histone modifications in DAM6 gene were investigated by chromatin immunoprecipitation in two different cultivars. • The expression of DAM4-DAM6 and several genes related to abscisic acid and drought stress response correlated with the dormancy behaviour of peach cultivars. The trimethylation of histone H3 at K27 in the DAM6 promoter, coding region and the second large intron was preceded by a decrease in acetylated H3 and trimethylated H3K4 in the region of translation start, coinciding with repression of DAM6 during dormancy release. • Analysis of chromatin modifications reinforced the role of epigenetic mechanisms in DAM6 regulation and bud dormancy release, and highlighted common features with the vernalization process in Arabidopsis thaliana and cereals. © 2011 The Authors. New Phytologist © 2011 New Phytologist Trust.

During fruit ripening a loss of firmness occurs, which is a key factor limiting postharvest life. In apricot, Prunus armeniaca L., a wide range of fruit firmness at commercial maturity has been observed in different cultivars. Endopolygalacturonase (endoPG) activity has been reported to be associated with differences in firmness in many fruit species, but never in apricot. In this paper, we reported the identification of an apricot cDNA (PaPG) coding for an endoPG-like protein with 393 amino acids. Protein sequence comparison with known polygalacturonases (PGs) revealed that multiple features as conserved domains and functional residues and a predicted signal peptide were present in PaPG. Moreover, a phylogenetic analysis of this and other plant PGs placed PaPG into a clade containing endoPGs expressed in fruit, abscission and dehiscence zones without a propeptide sequence, very close to PRF5 from peach (Prunus persica L. Batsch). PaPG gene expression increased during postharvest storage of the fruit, correlating with fruit softening and ethylene release, and it responded to exogenous ethylene treatments. We localized the PaPG gene in apricot linkage group 4 after genetic mapping based on SNP analysis, in a position apparently syntenic to the PRF5 locus from peach. Results obtained offer genetic evidence supporting the hypothesis that PaPG and PRF5 are orthologous genes, and consequently position PaPG as a gene of interest for studies on fruit softening in apricot, and contribute to the development of molecular tools for breeding apricots with longer shelf life. © 2011 Elsevier B.V. All rights reserved.

To better understand the molecular and physiological mechanisms underlying maintenance and release of seasonal bud dormancy in perennial trees, we identified differentially expressed genes during dormancy progression in reproductive buds from peach (Prunus persica [L.] Batsch) by suppression subtractive hybridization (SSH) and microarray hybridization. Four SSH libraries were constructed, which were respectively enriched in cDNA highly expressed in dormant buds (named DR), in dormancy-released buds (RD) and in the cultivars with different chilling requirement, 'Zincal 5' (ZS) and 'Springlady' (SZ), sampled after dormancy release. About 2500 clones picked from the four libraries were loaded on a glass microarray. Hybridization of microarrays with the final products of SSH procedure was performed in order to validate the selected clones that were effectively enriched in their respective sample. Nearly 400 positive clones were sequenced, which corresponded to 101 different unigenes with diverse functional annotation. We obtained DAM4, 5 and 6 genes coding for MADS-box transcription factors previously related to growth cessation and terminal bud formation in the evergrowing mutant of peach. Several other cDNAs are similar to dormancy factors described in other species, and others have been related to bud dormancy for the first time in this study. Quantitative reverse transcription polymerase chain reaction analysis confirmed differential expression of cDNAs coding for a Zn-finger transcription factor, a GRAS-like regulator, a DNA-binding protein and proteins similar to forisome subunits involved in the reversible occlusion of sieve elements in Fabaceae, among others. © The Author 2010. Published by Oxford University Press. All rights reserved.

Background The outer cell wall of the pollen grain (exine) is an extremely resistant structure containing sporopollenin, a mixed polymer made up of fatty acids and phenolic compounds. The synthesis of sporopollenin in the tapetal cells and its proper deposition on the pollen surface are essential for the development of viable pollen. The beginning of microsporogenesis and pollen maturation in perennial plants from temperate climates, such as peach, is conditioned by the duration of flower bud dormancy. In order to identify putative genes involved in these processes, we analyzed the results of previous genomic experiments studying the dormancy-dependent gene expression in different peach cultivars. Results The expression of 50 genes induced in flower buds after the endodormancy period (flower-bud late genes) was compared in ten cultivars of peach with different dormancy behaviour. We found two co-expression clusters enriched in putative orthologs of sporopollenin synthesis and deposition factors in Arabidopsis. Flower-bud late genes were transiently expressed in anthers coincidently with microsporogenesis and pollen maturation processes. We postulated the participation of some flower-bud late genes in the sporopollenin synthesis pathway and the transcriptional regulation of late anther development in peach. Conclusions Peach and the model plant Arabidopsis thaliana show multiple elements in common within the essential sporopollenin synthesis pathway and gene expression regulatory mechanisms affecting anther development. The transcriptomic analysis of dormancy-released flower buds proved to be an efficient procedure for the identification of anther and pollen development genes in perennial plants showing seasonal dormancy.