Genome-wide characterization of the tomato GASA family identifies SlGASA1 as a repressor of fruit ripening

Gibberellins(GAs)play crucial roles in a wide range of developmental processes and stress responses in plants.However,the roles of GA-responsive genes in tomato(Solanum lycopersicum)fruit development remain largely unknown.Here,we identify 17 GASA(Gibberellic Acid-Stimulated Arabidopsis)family genes in tomato.These genes encode proteins with a cleavable signal peptide at their N terminus and a conserved GASA domain at their C terminus.The expression levels of all tomato GASA family genes were responsive to exogenous GA treatment,but adding ethylene eliminated this effect.Comprehensive expression profiling of SlGASA family genes showed that SlGASA1 follows a ripening-associated expression pattern,with low expression levels during fruit ripening,suggesting it plays a negative role in regulating ripening.Overexpressing SlGASA1 using a ripening-specific promoter delayed the onset of fruit ripening,whereas SlGASA1-knockdown fruits displayed accelerated ripening.Consistent with their delayed ripening,SlGASA1-overexpressing fruits showed significantly reduced ethylene production and carotenoid contents compared to the wild type.Moreover,ripening-related genes were downregulated in SlGASA1-overexpressing fruits but upregulated in SlGASA1-knockdown fruits compared to the wild type.Yeast two-hybrid,co-immunoprecipitation,transactivation,and DNA pull-down assays indicated that SlGASA1 interacts with the key ripening regulator FRUITFULL1 and represses its activation of the ethylene biosynthesis genes ACS2 and ACO1.Our findings shed new light on the role and mode of action of a GA-responsive gene in tomato fruit ripening.

The persimmon(Diospyros oleifera Cheng)genome provides new insights into the inheritance of astringency and ancestral evolution

Persimmon(Diospyros kaki)is an oriental perennial woody fruit tree whose popular fruit is produced and consumed worldwide.The persimmon fruit is unique because of the hyperaccumulation of proanthocyanidins during fruit development,causing the mature fruit of most cultivars to have an astringent taste.In this study,we obtained a chromosome-scale genome assembly for‘Youshi’(Diospyros oleifera,2n=2x=30),the diploid species of persimmon,by integrating Illumina sequencing,single-molecule real-time sequencing,and high-throughput chromosome conformation capture techniques.The assembled D.oleifera genome consisted of 849.53 Mb,94.14%(799.71 Mb)of which was assigned to 15 pseudochromosomes,and is the first assembled genome for any member of the Ebenaceae.Comparative genomic analysis revealed that the D.oleifera genome underwent an ancientγwhole-genome duplication event.We studied the potential genetic basis for astringency development(proanthocyanidin biosynthesis)and removal(proanthocyanidin insolublization).Proanthocyanidin biosynthesis genes were mainly distributed on chromosome 1,and the clustering of these genes is responsible for the genetic stability of astringency heredity.Genome-based RNA-seq identified deastringency genes,and promoter analysis showed that most of their promoters contained large numbers of low oxygen-responsive motifs,which is consistent with the efficient industrial application of high CO2 treatment to remove astringency.Using the D.oleifera genome as the reference,SLAF-seq indicated that‘Youshi’is one of the ancestors of the cultivated persimmon(2n=6x=90).Our study provides significant insights into the genetic basis of persimmon evolution and the development and removal astringency,and it will facilitate the improvement of the breeding of persimmon fruit.

Ethylene†and fruit softening

This review is concerned with the mechanisms controlling fruit softening.Master genetic regulators switch on the ripening programme and the regulatory pathway branches downstream,with separate controls for distinct quality attributes such as colour,flavour,texture,and aroma.Ethylene plays a critical role as a ripening hormone and is implicated in controlling different facets of ripening,including texture change,acting through a range of transcriptional regulators,and this signalling can be blocked using 1-methylcyclopropene.A battery of at least seven cell-wall-modifying enzymes,most of which are synthesized de novo during ripening,cause major alterations in the structure and composition of the cell wall components and contribute to the softening process.Significant differences between fruits may be related to the precise structure and composition of their cell walls and the enzymes recruited to the ripening programme during evolution.Attempts to slow texture change and reduce fruit spoilage by delaying the entire ripening process can often affect negatively other aspects of quality,and low temperatures,in particular,can have deleterious effects on texture change.Gene silencing has been used to probe the function of individual genes involved in different aspects of ripening,including colour,flavour,ethylene synthesis,and particularly texture change.The picture that emerges is that softening is a multi-genic trait,with some genes making a more important contribution than others.In future,it may be possible to control texture genetically to produce fruits more suitable for our needs.

Research advance in regulation of fruit quality characteristics by microRNAs

MicroRNAs(miRNAs)are short(19-24 nucleotides in length)noncoding RNAs that have a profound effect on gene expression.By completely or almost perfectly base-pairing with their individual target mRNAs they cause mRNA cleavage or repression of translation.As important regulators,miRNAs plays an important role in the regulation of fruit quality.Extensive studies have been reported in fruits,however current studies are mostly focused on the identification of miRNAs and the prediction and validation of target genes.This review summarizes research progress on the role of miRNAs in regulating fruit ripening and senescence and quality characteristics,such as coloration,flavor metabolism,and texture for providing information for future research.

Plant genetic engineering and genetically modified crop breeding: history and current status

This review charts the major developments in the genetic manipulation of plant cells that have taken place since the first gene transfer experiments using Ti plasmids in 1983. Tremendous progress has been made in both our scientific understanding and technological capabilities since the first genetically modified(GM)crops were developed with single gene resistances to herbicides, insects, viruses, and the silencing of undesirable genes. Despite opposition in some parts of the world, the area planted with first generation GM crops has grown from 1.7 Mhm^2 in 1996 to 179.7 Mhm^2 in 2015.The toolkit available for genetic modification has expanded greatly since 1996 and recently Nobel Laureates have called on Greenpeace to end their blanket opposition,and plant scientists have urged that consideration be given to the benefits of GM crops based on actual evidence. It is now possible to use GM to breed new crop cultivars resistant to a much wider range of pests and diseases, and to produce crops better able to adapt to climate change.The advent of new CRISPR-based technologies makes it possible to contemplate a much wider range of improvements based on transfer of new metabolic pathways and traits to improve nutritional quality, with a much greater degree of precision. Use of GM, sometimes in conjunction with other approaches, offers great opportunities for improving food quality, safety, and security in a changing world.