63 research outputs found
Molecular and Genetic Regulation of Sensory Quality of Climacteric Fruit
The sensory quality of fruit has become a major criterion in making the
purchasing decision by consumers. Breeding programs have mainly been directed,
from the post-harvest stand point, towards improving shelf-life. Chance seedlings or
mutants with improved agronomic traits and/or extended shelf-life have been used
for introgressing the long shelf-life character and eventually improved sensory
quality traits in commercial genotypes of apple, melon or tomato. Because the plant
hormone ethylene plays a central role in both storability and ripening of climacteric
fruit, the generation by biotechnology of ethylene-inhibited fruit has offered a
powerful tool to better understand, at the molecular and genetic level, the interrelations
between storability and sensory quality. In the melon, inhibition of ethylene
synthesis results is a strong inhibition of the synthesis of aroma volatiles while the
accumulation of sugars is not affected or is even improved. The softening of the flesh
is strongly affected but not abolished. Mid or long shelf-life melons generated by
classical breeding present the same behavior. The generation of recombinant inbred
lines by crossing a typical climacteric melon (Cantaloupe Charentais of the
cantalupensis group) with a non climacteric melon (PI161375 of the agrestis
chinensis group) allowed to demonstrate that the climacteric character is conferred
by 2 duplicated loci only, which are of great importance for the regulation of
storability and sensory quality. Due to the importance of aroma volatiles in sensory
quality and to the strong negative correlation between aroma production and
ethylene synthesis, we have developed a research program aimed at isolating genes
involved in the synthesis of aroma volatiles. We will report on the recent advances in
the field with special emphasis on the characterization of genes responsible for the
synthesis of esters, a family of compounds crucial for the flavor of many fruit
ACC Synthase Genes Related to Cold-dependent Ripening in Pear Fruit
The differential regulation of ACC synthase genes has been studied in pear
cultivars that either require a long chilling treatment before they are capable of
ripening (‘Passe-Crassane’, PC) or not (‘Old-Home’, OH) and in OH x PC hybrids
having no (A16) or intermediate (A50) cold requirement. Among the seven Pc-ACS
cDNAs isolated, four of them (Pc-ACS1a/b and Pc-ACS2a/b) showed differential
expression in relation with cold requirement. Pc-ACS1a transcripts accumulated
specifically during chilling and ripening of cold-dependent cultivars while Pc-ACS1b
transcripts were detected only during ripening of cold-independent genotypes. Pc-
ACS2a mRNA was expressed specifically in cold-dependent genotypes and
negatively regulated by ethylene while Pc-ACS2b transcripts accumulated only in
cold-independent genotypes and positively regulated by ethylene. Pc-ACS3, 4 and 5
transcripts accumulation was similar in all genotypes, independently of coldrequirements
Transcriptome analysis of an apple (Malus × domestica) yellow fruit somatic mutation identifies a gene network module highly associated with anthocyanin and epigenetic regulation
An apple loss-of-colour fruit somatic mutation is likely the consequence of collective repression of a co-expression gene network module highly associated with anthocyanin and methylation in the promoter of MdMYB1
Molecular Control of Fruit Ripening and Sensory Quality of Charentais Melon
Traditional Charentais melons have a typical climacteric behavior with
ethylene playing a major role in the regulation of the ripening process. Genetic studies
using climacteric and non-climacteric types of Cucumis melo demonstrated that the
climacteric character is dominant and conferred by 2 duplicated loci only which are of
great importance for the regulation of storability and sensory quality. Commercial
varieties of Charentais melon with long shelf-life have been generated, some of them
by crossing with a non-ripening Charentais genotype (Vauclusien). The introduction
of the long shelf-life character resulted in undesirable loss of aroma volatiles
production. The inhibition of ethylene synthesis by knocking-down ACC oxidase gene
expression has been achieved in Charentais melon. It results is a strong inhibition of
the synthesis of aroma volatiles while the accumulation of sugars is not affected or is
even improved and the softening of the flesh is strongly affected but not abolished. It
was also demonstrated that ethylene-inhibited fruit exhibited better resistance to
chilling injury. Due to the importance of aroma volatiles in sensory quality and to the
strong negative correlation between aroma production and ethylene synthesis, we have
developed a research program aimed at isolating genes involved in the synthesis of
volatile esters, compounds that are essential for the flavor of Cantaloupe melons. We
report here on the recent advances in the field with special emphasis on the characterization
of two families of genes encoding aldehyde reductases and alcohol acyl
transferases
Characterization of Genes Involved in the Formation of Aroma Volatiles in "Charentais" Melon Fruit
Volatiles esters impart distinct characteristics to the fruit quality.
"Charentais" cantaloupe melon (Cucumis melo "cantalupensis") is characterized by
abundant sweetness and aromatic flavour. Plant alcohol acyl transferase (AAT)
genes have been identified and shown to be involved in aromas production. Recently,two cDNAs (Cm-AAT1 and Cm-AAT2) putatively involved in the formation of aroma volatile esters have been isolated from melon fruit. Cm-AAT1 protein exhibit alcohol acyl transferase activity while no such activity could be detected for Cm-AAT2. Two new cDNAs (Cm-AAT3 and Cm-AAT4) have been isolated from melon fruit that
showed 69% and 36% similarity, respectively, with Cm-AAT1. The percentage
similarity over the whole amino acid sequence between them is 34%. Cm-AAT3 and
Cm-AAT4 show the highest similarity to the tobacco Nt-HSR201 protein and a rose
alcohol acyltransferase Rh-AAT1, respectively. All Cm-AATs genes, share three
conserved regions common to the BAHD acyltransferase gene superfamily.
Heterologous expression in yeast revealed that some of the encoded proteins have a
wide range of specificity while others are specific to a narrow range of substrates
Prunus domestica Pathogenesis-Related Protein-5 Activates the Defense Response Pathway and Enhances the Resistance to Fungal Infection
Pathogenesis-related protein-5 (PR-5) has been implicated in plant disease resistance and its antifungal activity has been demonstrated in some fruit species. However, their roles, especially their interactions with the other defense responses in plant cells, are still not fully understood. In this study, we have cloned and characterized a new PR-5 cDNA named PdPR5-1 from the European plum (Prunus domestica). Expression of PdPR5-1 was studied in different cultivars varying in resistance to the brown rot disease caused by the necrotrophic fungus Monilinia fructicola. In addition transgenic Arabidopsis, ectopically expressing PdPR5-1 was used to study its role in other plant defense responses after fungal infection. We show that the resistant cultivars exhibited much higher levels of transcripts than the susceptible cultivars during fruit ripening. However, significant rise in the transcript levels after infection with M. fructicola was observed in the susceptible cultivars too. Transgenic Arabidopsis plants exhibited more resistance to Alternaria brassicicola. Further, there was a significant increase in the transcripts of genes involved in the phenylpropanoid biosynthesis pathway such as phenylalanine ammonia-lyase (PAL) and phytoalexin (camalexin) pathway leading to an increase in camalexin content after fungal infection. Our results show that PdPR5-1 gene, in addition to its anti-fungal properties, has a possible role in activating other defense pathways, including phytoalexin production
Recent Developments on the Role of Ethylene in the Ripening of Climacteric Fruit
It has long been recognised that ethylene plays a major role in the ripening
process of climacteric fruit. A more thorough analysis, however, has revealed that a
number of biochemical and molecular processes associated with climacteric fruit
ripening are ethylene-independent. One of the crucial steps of the onset of ripening
is the induction of autocatalytic ethylene production. In ethylene-suppressed melons,
ACC synthase activity is induced at the same time as in control melons, indicating
that ACC biosynthesis during the early stages of ripening seems to be a
developmentally-regulated (ethylene-independent) process. The various ripening
events exhibit differential sensitivity to ethylene. For instance, the threshold level for
degreening of the rind is 1ppm, while 2.5 ppm are required to trigger some
components of the softening process. The saturating level of ethylene producing
maximum effects is less than 5 ppm, which is by far lower than the internal ethylene
concentrations found in the fruit at the climacteric peak (over 100 ppm). In many
fruit chilling temperatures hasten ethylene production and ripening and in some late
season pear varieties, exposure to chilling temperatures is even absolutely required
for the attainment of the capacity to synthesize autocatalytic ethylene. This is
correlated with the stimulation of expression of ACC oxidase and of members of the
ACC synthase gene family. Ethylene operates via a perception and transduction
pathway to induce the expression of genes responsible for the biochemical and
physiological changes observed during ripening. However, only a few genes induced
via the ethylene transduction pathway have been described so far. We have used a
differential display method to isolate novel ethylene-reponsive (ER) cDNA clones of
tomato that potentially play a role in propagating the ethylene response and in
regulating fruit ripening. Collectively, these data permit a general scheme of the
molecular mechanisms of fruit ripening to be proposed
Identification and characterization of genes involved in the fruit color development of european plum
European plum fruit (Prunus domestica) are normally blue-black to dark purple. However, some genotypes remain green/yellow after ripening. We hypothesized that in such genotypes anthocyanin biosynthesis is genetically disturbed. To examine this hypothesis, six european plum genotypes with diverse fruit colors were investigated for the expression pattern of several anthocyanin biosynthetic genes (ABGs)—e.g., phenylalanine ammonia-lyase, chalcone synthase (CHS), dihydroflavonol 4-reductase (DFR), anthocyanin synthase (ANS), and UDP-glucose:flavonoid 3-O-glucosyltransferase 1 and 2 (UFGT 1 and 2). Expression profiles indicated that ABGs, especially Pd-CHS and UFGT 2, were significantly downregulated in the green/yellow fruit compared with the dark-purple fruit. Furthermore, the quantification of total polyphenols and individual flavonoid compounds showed substantial differences between the off-colored and the purple genotype. To further examine the contribution of each of the ABGs in color development, the open reading frame (ORP) of Pd-CHS, Pd-DFR, Pd-ANS, and Pd-UFGT 2 was ectopically expressed in tobacco (Nicotiana tabacum). The characterization of transgenic plants showed that the petals of plants expressing Pd-CHS were darker in color and had higher anthocyanin content than control or even other transgenic types, suggesting the significant contribution of CHS in determining anthocyanin production levels and hence fruit coloration. The results of this study provides better understanding of color development in european plum, which can be rewarding in developing european plum cultivars with desired colors through classical or modern breeding tools
Differential regulation of ACC synthase genes in cold-dependent and -independent ripening in pear fruit
Late pear cultivars such as Passe-Crassane (PC) require a long chilling treatment before they are capable of ripening. Early cultivars such as Old-Home (OH) have no cold prerequisite. The regulation of 1-aminocyclopropane-1-carboxylic acid synthase (ACS) genes was studied in OH, PC and in OH x PC hybrids in order to determine the role of this gene family in the cold requirement. Of the seven Pc-ACS cDNAs isolated, four (Pc-ACSla/b and Pc-ACS2a/b) showed differential expression associated with the cold requirement. Pc-ACS1a transcripts accumulated throughout the cold treatment and, with Pc-ACS2a, during ripening of cold-dependent cultivars. Pc-ACS1b and Pc-ACS2b were detected only during ripening of cold-independent genotypes. Furthermore, Pc-ACS2a transcript accumulation was negatively regulated by ethylene, whereas Pc-ACS2b was positively regulated by the hormone. Pc-ACS3, 4 and 5 transcript accumulation was similar in all genotypes. Genetic analyses of OH, PC, and 22 OH x PC progenies demonstrated that late, cold-dependent cultivars were homozygous for Pc-ACS1a and 2a whereas early, cold-independent cultivars were heterozygous for Pc-ACS1(a/b) and homozygous for Pc-ACS2b. A model is presented in which differences in Pc-ACS alleles and gene expression between cold- and non-cold-requiring pears are critical in determining the ripening behaviour of the cultivars
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