Molecular biology of fruit ripening and its manipulation with antisense genes

Abstract

Considerable progress in tomato molecular biology has been made over the past five years. At least 19 different mRNAs which increase in amount during tomato fruit ripening have been cloned and genes for enzymes involved in cell wall degradation (polygalacturonase and pectinesterase) and ethylene synthesis (ACC synthase) have been identified by conventional procedures. Transgenic plants have been used to identify regions of DNA flanking fruit-specific, ripening-related and ethylene-regulated genes and trans-acting factors which bind to these promoters have also been identified. Antisense genes expressed in transgenic plants have proved to be highly effective for inhibiting the specific expression of ripening-related genes. These experiments have changed our understanding of how softening occurs in tomato fruit. Antisense techniques have also been used to identify genes encoding enzymes for carotenoid biosynthesis (phytoene synthase) and ethylene biosynthesis (the ethylene-forming enzyme). The altered characteristics of fruit transformed with specific antisense genes, such as retarded ripening and resistance to splitting, may prove to be of value to fruit growers, processors and ultimately the consumer.

Folate synthesis in plants: The first step of the pterin branch is mediated by a unique bimodular GTP cyclohydrolase I

“…The steep decline in GCHI expression after the mature green stage, when folate levels begin to fall, implies a collapse of the fruit's capacity to maintain its folate-synthesis machinery, and hence to sustain its folate levels in the face of ongoing turnover. The collapse in GCHI expression presumably is programmed, because ripeningrelated genes are still being induced when it occurs (37). Fruit folate content therefore might be enhanced by prolonging the expression of GCHI and perhaps other folate-synthesis enzymes.…”

The SOL Genomics Network. A Comparative Resource for Solanaceae Biology and Beyond

“…The Solanaceae are the third most important plant taxon economically, the most valuable in terms of vegetable crops, and the most variable of crop species in terms of agricultural utility. In addition to their role as important food sources, many solanaceous species have a role as scientific model plants, such as tomato and pepper, for the study of fruit development (Gray et al, 1992;Fray and Grierson, 1993;Hamilton et al, 1995;Brummell and Harpster, 2001;Alexander and Grierson, 2002;Adams-Phillips et al, 2004;Giovannoni, 2004;Tanksley, 2004), potato for tuber development (Prat et al, 1990;Fernie and Willmitzer, 2001), petunia for the analysis of anthocyanin pigments, and tomato and tobacco (Nicotiana tabacum) for plant defense (Bogdanove and Martin, 2000;Gebhardt and Valkonen, 2001;Li et al, 2001;Pedley and Martin, 2003). The Solanaceae genomes have undergone relatively few genome rearrangements and duplications and therefore have very similar gene content and order.…”

TGTCACA Motif Is a Novel cis-Regulatory Enhancer Element Involved in Fruit-specific Expression of the cucumisin Gene

“…A number of fruit-specific genes that are activated during ripening have been isolated from tomato and other fruits, and genes responding to ethylene and nonethylene signals have been identified (1,2). The promoters of fruit-specific genes would also be of great interest for use in strategies to manipulate fruit metabolism and produce valuable proteins such as antibody, biopharmaceuticals, and edible vaccines through methods of genetic engineering (3)(4)(5). However, the detailed mechanisms by which the expression of fruit protein genes are regulated are poorly understood, as many of the essential cis-elements have not been identified.…”