ISHS Acta Horticulturae 297: II International Symposium on Kiwifruit
EXPRESSION OF ACTINIDIN, A KIWIFRUIT CYSTEINE PROTEASE |
| Authors: | E. Podivinsky, Kim C. Snowden, J. Keeling, E. Lin, R. C. Gardner |
| Abstract:
The cysteine protease actinidin is abundant in fruit of kiwifruit. Although its biological role is unknown, its X-ray structure has been determined and cDNA clones encoding the protein have been isolated and sequenced. Our current data suggest that the protein is produced by a large multigene family. cDNA sequencing has revealed that there is a second actinidin gene family expressing a basic protein (pl 8.8 rather than 4.5 for the mature acidic protein). The basic actinidins are also encoded by a gene family and are about 80% homologous to the acidic class. The presence of basic and acidic isoforms of actinidin is reminiscent of PR proteins, which have a role in defence against pathogen attack. By analogy we suggest that actinidin may play a similar role, and that the basic and acidic isoforms may be present in different cellular compartments. Expression of actinidin occurs in fruit after they have attained about half their full size, and the level of mRNA increases during ripening. mRNA of the basic actinidin class is present at about one tenth of the abundance of the acidic actinidins, which constitute a few percent of the total message. A genomic clone for an acidic gene has been sequenced, and promoter regions from several acidic genes have been obtained by inverse PCR. GUS fusions have been constructed with these promoters and the chimaeric genes introduced into transgenic petunias and into kiwifruit. Results of these experiments will be presented. | |
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