The role of acyl carrier protein in strawberry fruit ripening

Abstract

Strawberry (Fragaria ananassa) is an economically important soft fruit that is highly valued as a fresh product and flavouring. During ripening, strawberry fruits undergo a number of physiological changes affecting colour, texture and flavour. An understanding of these changes at the biochemical and molecular level will be important in developing strategies for enhancing the quality attributes of this fruit. A cDNA encoding a ripening- enhanced acyl carrier protein (RE-ACP) was previously isolated from strawberry fruit. AC? is an essential component of fatty acid synthesis in both plants and animals. The aims of this thesis were to isolate and characterise this and other members of the ACP multigene family expressed in strawberry fruit. Six closely related putative AC? cDNA isoforms were identified from strawberry. Two of these were obtained by screening a cDNA library from ripe fruit and three were obtained by a technique known as candidate fragment length polymorphism (CFLP) that utilised ACP gene-specific primers for AFLP-cDNA display. Northern analysis was not able to differentiate their expression but ACP was highly up-regulated in ripening fruit whereas low levels of expression were detected in other strawberry tissues, including achenes (seeds), expanding leaves and flowers. The RE-ACP was over-expressed in E. coli and the recombinant protein partially purified. The over-expressed protein had a M(_r) of 20kDa on SDS-PAGE and appeared to form a dimer. A genomic library was constructed from F. ananassa from which two different genomic clones closely related to RE-ACP were obtained. Promoter analysis indicated the presence of regulatory elements. The characterization of putative ACP cDNA and genomic clones, including the 5' upstream regions, is described and their possible role in strawberry fruit is discussed. Key words: Strawberry, fruit, ripening, gene expression, genomic, cDNA, fatty acid, acyl carrier protein, aroma, promoter.