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Summary: In temperate zones, fruit trees regulate their annual growth cycle to seasonal environmental changes. During the cold season, growth is limited by both environmental and genetic factors. After the exposure to low temperature and fulfillment of chilling requirements, mild temperatures promote the growth and flowering. However, an insufficient chilling exposure may lead to nonuniform blooming, with a negative impact on fruit set.To gain insights into flower development in the fruit tree buds, peach is an interesting model, the flower and vegetative bud being distinct organs. To understand how flower bud development is regulated, we integrated cytological observations and epigenetic and chromatin genome‐wide data with transcriptional changes to identify the main regulatory factors involved in flower development during chilling accumulation.We demonstrated that growth cessation does not occur in peach flower buds during chilling accumulation, but that there are changes in transcript abundance of key genes of hormone metabolism and flower bud development, distribution of histone modifications (H3K4me3 and H3K27me3) and DNA methylation.Altogether, our findings indicate that during the cold season the flower bud is in a nondormant state and that the chilling experience allows flower differentiation to be completed. [ABSTRACT FROM AUTHOR]

Differences in gene expression were studied after Plum pox virus ( PPV, sharka disease) infection in peach GF305 leaves with and without sharka symptoms using RNA-Seq. For each sample, more than 80% of 100-nucleotide paired-end ( PE) Illumina reads were aligned on the peach reference genome. In the symptomatic sample, a significant proportion of reads were mapped to PPV reference genomes (1.04% compared with 0.00002% in non-symptomatic leaves), allowing for the ultra-deep assembly of the complete genome of the PPV isolate used (9775 nucleotides, missing only 11 nucleotides at the 5′ genome end). In addition, significant alternative splicing events were detected in 359 genes and 12 990 single nucleotide polymorphisms ( SNPs) were identified, 425 of which could be annotated. Gene ontology annotation revealed that the high-ranking mRNA target genes associated with the expression of sharka symptoms are mainly related to the response to biotic stimuli, to lipid and carbohydrate metabolism and to the negative regulation of catalytic activity. A greater number of differentially expressed genes were observed in the early asymptomatic phase of PPV infection in comparison with the symptomatic phase. These early infection events were associated with the induction of genes related to pathogen resistance, such as jasmonic acid, chitinases, cytokinin glucosyl transferases and Lys- M proteins. Once the virus had accumulated, the overexpression of Dicer protein 2a genes suggested a gene silencing plant response that was suppressed by the virus HCPro and P1 proteins. These results illustrate the dynamic nature of the peach- PPV interaction at the transcriptome level and confirm that sharka symptom expression is a complex process that can be understood on the basis of changes in plant gene expression. [ABSTRACT FROM AUTHOR]

Peach ( Prunus persica var. laevis Gray) was chosen to unravel the molecular basis underlying the ability of spermidine (Sd) to influence fruit development and ripening. Field applications of 1 m M Sd on peach fruit at an early developmental stage, 41 days after full bloom (dAFB), i.e. at late stage S1, led to a slowing down of fruit ripening. At commercial harvest (125 dAFB, S4II) Sd-treated fruits showed a reduced ethylene production and flesh softening. The endogenous concentration of free and insoluble conjugated polyamines (PAs) increased (0.3-2.6-fold) 1 day after treatment (short-term response) butsoon it declined to control levels; starting from S3/S4, when soluble conjugated forms increased (up to five-fold relative to controls at ripening), PA levels became more abundant in treated fruits, (long-term response). Real-time reverse transcription-polymerase chain reaction analyses revealed that peaks in transcript levels of fruit developmental marker genes were shifted ahead in accord with a developmental slowing down. At ripening (S4I-S4II) the upregulation of the ethylene biosynthetic genes ACO1 and ACS1 was dramatically counteracted by Sd and this led to a strong downregulation of genes responsible for fruit softening, such as PG and PMEI. Auxin-related gene expression was also altered both in the short term ( TRPB) and in the long term ( GH3, TIR1 and PIN1), indicating that auxin plays different roles during development and ripening processes. Messenger RNA amounts of other hormone-related ripening-regulated genes, such as NCED and GA2-OX, were strongly downregulated at maturity. Results suggest that Sd interferes with fruit development/ripening by interacting with multiple hormonal pathways. [ABSTRACT FROM AUTHOR]

• The time course of ethylene biosynthesis and perception was investigated in ripening peach fruit ( Prunus persica) following treatments with the polyamines putrescine (Pu) and spermidine (Sd), and with aminoethoxyvinylglycine (AVG). • Fruit treatments were performed in planta. Ethylene production was measured by gas chromatography, and polyamine content by high-performance liquid chromatography; expression analyses were performed by Northern blot or real-time polymerase chain reaction. • Differential increases in the endogenous polyamine pool in the epicarp and mesocarp were induced by treatments; in both cases, ethylene production, fruit softening and abscission were greatly inhibited. The rise in 1-aminocyclopropane-1-carboxylate oxidase ( PpACO1) mRNA was counteracted and delayed in polyamine-treated fruit, whereas transcript abundance of ethylene receptors PpETR1 (ethylene receptor 1) and PpERS1 (ethylene sensor 1) was enhanced at harvest. Transcript abundance of arginine decarboxylase (ADC) and S-adenosylmethionine decarboxylase (SAMDC) was transiently reduced in both the epicarp and mesocarp. AVG, here taken as a positive control, exerted highly comparable effects to those of Pu and Sd. • Thus, in peach fruit, increasing the endogenous polyamine pool in the epicarp or in the mesocarp strongly interfered, both at a biochemical and at a biomolecular level, with the temporal evolution of the ripening syndrome. [ABSTRACT FROM AUTHOR]

The characterization and expression of PP-ACO1 and PP-ACO2, two members of the peach 1-aminocyclopropane-1-carboxylate (ACC) oxidase (ACO) gene family, are reported. PP-ACO1 is organized in 4 exons interrupted by 3 introns, whereas PP-ACO2 has only 2 of the 3 introns present in PP-ACO1. Comparison of the deduced amino acid sequences of PP-ACO1 and PP-ACO2 reveals a 77.7% identity. PP-ACO1 and PP-ACO2 show highest degree of similarity with petunia (PH-ACO3; 84.1%) and apple (85.4%) ACO genes, respectively. PP-ACO1 is expressed in flowers, fruitlet abscission zones, mesocarp and in young fully expanded leaves. PP-ACO1 transcript accumulation strongly increases during fruitlet abscission, in ripe mesocarp and senescing leaves, and is enhanced by propylene. PP-ACO2 mRNA accumulation is detected in fruits only during early development and is unaffected by propylene treatment. Both ACO genes are expressed in epicotyl and roots of growing seedlings, although a stronger accumulation of PP-ACO2 mRNA is observed. [ABSTRACT FROM AUTHOR]

During peach (Prunus persica [L.] Batsch) fruit development and ripening the cell wall undergoes several structural and biochemical changes driven by several hydrolases. Among these, the endo-β-1,4-D-glucanase (EGase, EC 3.2.1.4), or cellulase, may play a crucial role. Involvement of EGase throughout development and ripening of the fruit of cv. Redhaven was assessed by monitoring enzyme activity, specific polypeptide accumulation and gene transcription. During the four stages of growth EGase activity was high during S1 and in the early S2, declined during S3, and increased with the onset of ripening (S4). Two isoforms with isolectric points of 6.5 and 9.5 were identified. The pI 6.5 EGase was the only form present during the early stages of growth. whereas the pI 9.5 EGase was most abundant during ripening. The same isoforms were present in leaf and fruit abscission zones. The antibody raised against the pI 9.5 EGase, purified from leaf abscission zones, cross-reacted with a protein of 54 kDa. A cDNA clone of 753 bp encoding peach EGase was obtained by RT-PCR. EGase transcripts, detectable only after amplification of total RNA by RT-PCR, were observed during S1, and at the preclimacteric and climacteric stages. However, the strongest hybridisation occurred at ripening, in correspondence with the maximal enzyme activity and polypeptide accumulation, which took place before the ethylene climacteric and in the early stage of flesh softening. Propylene treatments reduced EGase activity during the early stage of fruit growth but dramatically enhanced enzyme activity and the related transcript accumulation at ripening, and accelerated the loss of firmness. In fruit treated with 2,5-norbornadiene the softening process was strongly inhibited and the rise in EGase transcripts and activity did not take place. The results point to the EGases being involved in early fruit growth and the initial phases of softening. The presence of two isoforms and the dual effect of propylene on enzyme activity suggest that different EGase genes operate during the early and late developmental stages in peach fruit. [ABSTRACT FROM AUTHOR]