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Genetic transformation of mango cultures potentially allows the transfer of different genes to manipulate specific processes. Nevertheless, genetic manipulation of any crop requires that relevant genes should be available. Mango genes have been identified that are, for the most part, associated with fruit ripening.

Mango fruit ripening is climacteric, and overripening, caused by the rapid increase in ethylene biosynthesis, occurs simultaneously with the climacteric peak (Tucker and Grierson, 1987). Consequently, mango fruit have poor storage quality. Genetic manipulation of mango fruit ripening to extend storage life by manipulation of genes that code for enzymes involved in ethylene biosynthesis has been an important focus.

Ripening-related genes have been studied at the molecular level. López-Gómez and Gómez-Lim (1992) and Chaimanee et al. (1999) reported changes in mRNA and protein accumulation during fruit ripening, and Gómez-Lim (1993) isolated cDNAs for mango aminocyclopropane-1-carboxylate (ACC) synthase and ACC oxidase. Gómez-Lim (1993) demonstrated that the expression of ACC oxidase is before ACC synthase and ripening proceeds from the inside to the exterior of mango fruit. In contrast, ethylene-treated mango fruit show ACC oxidase and ACC synthase both appear initially in the peel.

A cDNA coding for a mango ethylene receptor has been isolated (Gutiérrez-Martinez et al., 2001). The message seems to be present at low levels in immature fruit and increases as the fruit ripens. Several candidate genes involved in ethylene biosynthesis have been identified from cDNA libraries of various mango cultivars as either complete or partial sequences (see GenBank): aminocyclopropane-1-carboxylic acid synthase (ACC synthase), 1-aminocyclopropane-1-carboxylic acid oxidase (ACC oxidase U22523, AF170705, AJ505612), EtR1-homologue ethylene receptor (AF227742), etc. Cell wall components are degraded and modified during fruit ripening. Genes for cell wall-metabolizing enzymes have been cloned from ripening mango fruit, e.g. β-galactosidase (AJ505585, AJ505584), β-glucanase (EF608067, AJ505607), pectic lyase, polygalacturonase (EU805508) and xyloglucan endotransglycosylase (AY600965) (see GenBank). Zainal et al. (1996) isolated a homologue of the Rab11/YPT3 group of GTP-binding proteins and suggested that it might be involved in secretion of hydrolases during mango fruit ripening. β-Glucanase and pectic lyase are only expressed in fruit tissue during ripening (Chourasia et al., 2006, 2008), and a ripening-related expansin gene that is responsive to ethylene is associated with fruit softening (Sane et al., 2005).

Bojórquez and Gómez-Lim (1995) demonstrated that aroma and flavour compounds are generated during fatty acid metabolism via the β-oxidation pathway. Cruz-Hernández and Gómez-Lim (1995) showed that alternative oxidase activity is correlated with heat production resulting in release of volatile aroma compounds and post-climacteric senescence. Other genes that are upregulated during mango fruit ripening include peroxisomal thiolase and acyl CoA oxidase. Aharoni et al. (2000) noted that a cDNA coding for alcohol acyl transferase from mango fruit appears to be involved in flavour compound synthesis. Alternative oxidases (AF329898, X79329) and a mitochondrial uncoupling protein that are differentially expressed during mango fruit ripening have been isolated (see GenBank; Considine et al., 2001).

Lower amylase activity and less total and reducing sugars have been measured in spongy tissue. Several cDNAs have been identified in tissue affected by internal breakdown or ‘jelly seed’ and from healthy tissue (see GenBank). Vasanthaiah et al. (2006) determined gene expression differences of healthy and spongy mesocarp tissue, and those that encoded alcohol dehydrogenase, catalase, coproporphyrinogen oxidase, keratin-associated protein and ubiquitin were upregulated in spongy tissue. Cystathionine gamma synthase, fructose biphosphate aldolase and ribosomal protein expression were reduced. Vasanthaiah et al. (2006) suggested that oxidative stress could contribute to spongy tissue development.