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

Contribution of genomics to postharvest biology

Purpose of review: This review aims at presenting the actual and potential contribution of genomics to the understanding of the fruit ripening process and to the genetic improvement of fruit quality and storability. Findings: The advent of high throughput technologies for the sequencing of mRNAs and genomic DNA has sped up the study of gene expression and the decoding of the genome of fruit species. Genomic resources are now available that facilitate the definition of molecular markers for marker-assisted breeding, the functional identification of genes involved in fruit quality traits, the understanding of the network of events underlying the fruit ripening process and of the impact of external factors such as postharvest treatments. Directions for future research: Up to now, the development of genomic tools for studying the fruit ripening process have been carried out mostly using tomato as a model fruit. There is a need for applying genomic methods to the understanding of fruit ripening in other species, particularly non-climacteric fruit. Efforts should also be directed towards the elucidation of the function of the genes in planta and of the regulation of their expression. So far, among the several hundreds of genes whose expression is altered during ripening, very few have well characterized functions. The number of genes for which a picture of the regulatory events is available is extremely limited

Mechanism of Fruit Ripening - Chapter 16

The fruit ripening process has been viewed over the last decades as being successively of physiological, biochemical, and molecular nature. Fruit ripening is accompanied by a number of biochemical events, including changes in color, sugar, acidity, texture, and aroma volatiles that are crucial for the sensory quality (Fig. 16.1). At the late stages of ripening, some senescence-related physiological changes occur that lead to membrane deterioration and cell death. In that regard, fruit ripening can thus be considered as the first step of a programmed cell death process. All biochemical and physiological changes that take place during fruit ripening are driven by the coordinated expression of fruit ripening-related genes. These genes encode enzymes that participate directly in biochemical and physiological changes. They also encode regulatory proteins that participate in the signaling pathways, and in the transcriptional machinery that regulate gene expression and set in motion the ripening developmental progra

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

A reliable system for the transformation of cantaloupe charentais melon (Cucumis melo L. var. cantalupensis) leading to a majority of diploid regenerants

An efficient system of transformation leading to a majority of transformed diploid plants from leaf explants of Cucumis melo L. var. Cantalupensis (cv. Védrantais) was developed. Several regeneration protocols using cotyledon or leaf explants were analysed with particular emphasis on the regeneration efficiency and the ploidy level of the regenerated melon plants. The use of leaf explants excised from 10 day-old seedlings, cultured in Murashige and Skoog's medium supplemented with 1 mM 6-benzylaminopurine (BAP) and 1 mM 6-(g,g-dimethylallylamino)-purine (2iP), resulted in a high regeneration frequency (73%). In these conditions, more than 84% of the regenerated plants were found to be diploid. Addition of an Agrobacterium-mediated transformation step did not significantly change the percentage (81.8%) of diploid plants regenerated. This protocol was successfully used to produce diploid transgenic melon plants expressing the antisense ACC oxidase gene, encoding ACC oxidase which catalyses the last step of ethylene biosynthesis. Ethylene production and ACC oxidase activity of the leaf explants from transgenic plants was reduced by more than 80% as compared to the control untransformed tissues. This transformation/ regeneration method could be routinely used for the introduction of other genes of interest in melon

Regulation of tomato fruit ripening

Fruit ripening is a sophisticatedly orchestrated developmental process, unique to plants, that results in major physiological and metabolic changes, ultimately leading to fruit decay and seed dispersal. Because of their strong impact on fruit nutritional and sensory qualities, the ripeningassociated changes have been a matter of sustained investigation aiming at unravelling the molecular and genetic basis of fruit ripening. Tomato rapidly emerged as the model of choice for fleshy fruit research and a wealth of genetic resources and genomics tools have been developed, providing new entries into the regulatory mechanisms involved in the triggering and coordination of the ripening process. Some of the key components participating in the control of tomato fruit ripening have been uncovered, but our knowledge of the network of signalling pathways engaged in this complex developmental process remains fragmentary. This review highlights the main advances and emphasizes issues still to be addressed using the rapidly developing ‘omics’ approaches

Potential for Ethanol Vapours to Limit Table Grape Berry Shatter and to Limit Ethylene Evolution from Clusters

We have shown previously that ethanol vapours (given by 2 ml per kg of grapes) can prevent Botrytis development and stem browning, two of the major problems in postharvest quality of table grapes. In the present paper, we will give emphasis to preliminary results about (i) the role of ethanol vapours in the inhibition of berry shatter and (ii) the control of ethylene evolution from grapes bunches by ethanol vapours and the link to the control of Botryti

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

ER5, a tomato cDNA encoding an ethylene-responsive LEA-like protein: characterization and expression in response to drought, ABA and wounding

We report the isolation by differential display of a novel tomato ethylene-responsive cDNA, designated ER5. RT-PCR analysis of ER5 expression revealed an early (15 min) and transient induction by ethylene in tomato fruit, leaves and roots. ER5 mRNA accumulated during 2 h of ethylene treatment and thereafter underwent a dramatic decline leading to undetectable expression after 5 h of treatment. The full-length cDNA clone of 748 bp was obtained and DNA sequence analysis showed strong homologies to members of the atypical hydrophobic group of the LEA protein family. The predicted amino acid sequence shows 67%, 64%, 64%, and 61%sequence identity with the tomato Lemmi9, soybean D95-4, cotton Lea14-A, and resurrection plant pcC27-45 gene products, respectively. As with the other members of this group, ER5 encodes a predominantly hydrophobic protein. Prolonged drought stress stimulates ER5 expression in leaves and roots, while ABA induction of this ethylene-responsive clone is confined to the leaves. The use of 1-MCP, an inhibitor of ethylene action, indicates that the drought induction of ER5 is ethylene-mediated in tomato roots. Finally, wounding stimulates ER5 mRNA accumulation in leaves and roots. Among the Lea gene family this novel clone is the first to display an ethylene-regulated expression