Survey of the expression of genes for ethylene synthesis and perception during maturation and ripening of 'Sunrise' and 'Golden Delicious' apple fruit

Ethylene is important in the ripening of apple fruit and different cultivars of apple show very different ripening patterns. The patterns of expression of the currently known genes for ethylene synthesis and perception in apple were examined for the summer apple, `Sunrise' (SR), and the later season `Golden Delicious' (GD). Comparisons were made during the last 4 weeks of maturation on the tree and after post-harvest ripening using reverse transcriptase quantitative PCR. Increases in gene expression for ACC synthase 1 (ACSI) and ACC Oxidase 1 (ACOI) were 1000- and 10,000-fold, respectively, for both cultivars confirming the importance of these genes in the climacteric ethylene burst. ACS1 levels remained below detection level until the ripening stage. Additional apple genes for ACS and ACO did not appear to contribute to this ripening-associated ethylene. ACS3 gene expression in both cultivars increased 100-fold during maturation and reached near maximum levels a full week before commercial harvest. Unique DNA sequences for apple ethylene receptors ETR2 and ETR5 and ethylene control element CTR1 were determined. Expression of four ethylene receptors (ETR1, 2, 5 and ERS1) and two control elements, CTRL and EIN2, were evaluated. Only small changes (less than 5-fold) were observed for these perception elements. Splice variants of CTRL did not appear to be differentially expressed in these tissues. Genes for ACO3 and ERS1 (in GD) responded in a fashion consistent with feedback inhibition of ethylene production in ripening tissue. Differences between the cultivars included a more gradual increase for ACO1 in GD, an increase in ERS1 for GD upon ripening that was not seen in SR, and a larger decrease in expression of CTR1 for GD compared with SR. (C) 2007 Elsevier B.V. All rights reserved.