Abstract
To reveal the feedback regulation of ABA biosynthesis, we examined ABA contents in dry seed using ABA-insensitive mutants (abi3, abi4,abi5). The abi3,abi5 mutants contained higher ABA contents in dry seeds compared to that of wild type. ABI3 protein contains 3 conserved domains (B1, B2 and B3). The abi3 alleles harboring the mutation in each domain were examined by measuring ABA content in dry seeds. Interestingly, the B2 and B3 mutants, but not the B1 mutant, accumulated more ABA than wild type. On the other hand, ABA content in the abi4 dry seeds was comparable to that in wild type. However, the reduction of mRNA levels of ABA biosynthesis genes in the abi4 mutant was more significant than that in wild type during imbibition. These results indicate that ABI4 is the positive, but ABI3 and ABI5 are the negative regulators of ABA biosynthesis during germination.
