Molecular cloning of cDNAs for auxin-induced mRNAs and developmental expression of the auxin-inducible genes.

By differential hybridization, two auxin-inducible cDNA clones (lambda SAR1 and lambda SAR2) have been isolated from a cDNA library constructed to poly(A)+ mRNA from auxin-treated strawberry receptacles. Both the clones have been used as probes to study the expression of the auxin-induced genes in pollinated and unpollinated fruits of various stages of development and in different organs. A high level of auxin-induced mRNAs is found in pollinated fruits as compared to unpollinated fruits of the same age, suggesting that the expression of the auxin-induced genes is developmentally regulated and the level of auxin-induced mRNAs is regulated by endogenous auxin. Furthermore, our data on the expression of lambda SAR1 and lambda SAR2 genes in pollinated and unpollinated fruits revealed a positive correlation between growth of strawberry fruit and the induction of mRNA corresponding to the lambda SAR1 and lambda SAR2 clones. Ethylene has no effect on the expression of the auxin-induced mRNAs. lambda SAR1 mRNA is not detected in other parts of strawberry plants whereas lambda SAR2 mRNA is present in roots. Furthermore, mRNA corresponding to lambda SAR1 and lambda SAR2 is not detected in other auxin-responsive plant systems such as pea epicotyls and bean explants.