Abstract
BackgroundExtensive studies have demonstrated that the COBRA gene is critical for biosynthesis of cell wall constituents comprising structural tissues of roots, stalks, leaves and other vegetative organs, however, its role in fruit development and ripening remains largely unknown.ResultsWe identified a tomato gene (SlCOBRA-like) homologous to Arabidopsis COBRA, and determined its role in fleshy fruit biology. The SlCOBRA-like gene is highly expressed in vegetative organs and in early fruit development, but its expression in fruit declines dramatically during ripening stages, implying a primary role in early fruit development. Fruit-specific suppression of SlCOBRA-like resulted in impaired cell wall integrity and up-regulation of genes encoding proteins involved in cell wall degradation during early fruit development. In contrast, fruit-specific overexpression of SlCOBRA-like resulted in increased wall thickness of fruit epidermal cells, more collenchymatous cells beneath the epidermis, elevated levels of cellulose and reduced pectin solubilization in the pericarp cells of red ripe fruits. Moreover, transgenic tomato fruits overexpressing SlCOBRA-like exhibited desirable early development phenotypes including enhanced firmness and a prolonged shelf life.ConclusionsOur results suggest that SlCOBRA-like plays an important role in fruit cell wall architecture and provides a potential genetic tool for extending the shelf life of tomato and potentially additional fruits.
Highlights
Extensive studies have demonstrated that the COBRA gene is critical for biosynthesis of cell wall constituents comprising structural tissues of roots, stalks, leaves and other vegetative organs, its role in fruit development and ripening remains largely unknown
COBRA gene family members in tomato In order to identify tomato orthologs of the COBRA gene, we ran a Basic Local Alignment Search Tool (BLAST) search in the SOL Genomics Network (SGN, http://solgenomics.net/) using the Arabidopsis COBRA gene sequence (AtCOB, accession No AF319663.1) as query. 17 unigene tomato cDNAs homologous to AtCOB were found in the SGN database and were designated as SlCOBLs (Table 1)
We focused further analyses on SlCOBRA-like as it appeared to be constitutively expressed in many tomato tissues suggesting an essential role in tomato biology
Summary
Extensive studies have demonstrated that the COBRA gene is critical for biosynthesis of cell wall constituents comprising structural tissues of roots, stalks, leaves and other vegetative organs, its role in fruit development and ripening remains largely unknown. The ripening of fleshy fruits involves a number of physiological processes including the production of aromatic compounds, nutrients, pigmentation, and softening of flesh to an edible texture [1,2] These processes have direct impacts on fruit firmness, color, flavor and nutritional content, and on shelf life, consumer acceptability, processing qualities, in addition to pre- and postharvest disease resistance [1,2]. Suppression of single genes encoding fruit PG [3,11] or PME [7,12] in transgenic tomato plants had limited impact on fruit softening during ripening, but conferred longer shelf life resulting from reduced susceptibility to postharvest pathogens These results suggest that suppression of certain enzymes acting on cellulose, hemicellulose or pectin alone are not sufficient to prevent softening, likely due to functional redundancy of enzymes involved in what is likely a complex metabolic process [1]. These enzymes have been shown to break glycosidic bonds between carbohydrates, or between carbohydrates and noncarbohydrate structural molecules [13]
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