Molecular and morphological analyzes of floral organs in an asparagus homeotic mutant

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Two vegetative lines of 'Gold Schatz' asparagus were introduced to Japan from the East Germany in 1966 and maintained in Hokkaido University through a vegetative propagation. One of these lines developed flowers with small tepals showing green color. Stamens were not found, but floral organs resembling the carpel differentiated at whorl 3 (stamen whorl). These adventitious carpels differentiated ovules including an embryo sac and egg cell. These morphological features suggested that the 'Gold Schatz' line might be a homeotic mutant of floral organogenesis, caused by a functional loss of class-B MADS-box genes.Southern blot analysis indicated that there was no difference in banding patterns of DNA fragments between wild type and mutant plants, when probed with DNA fragments specific for each of class-B and class-C MADS-box genes. Then, the expression of the MADS-box genes (AOAG1 and AOAG2 for class-C and AODEF, AOGLOA and AOGLOB for class-B genes) in wild type and mutant flowers was examined by Northern blot analysis. As a result, the expression of the B-functional genes were detected only in the wild type or scarcely detected in the mutant flowers. The expression of C-functional gene was detected in flowers from both lines. The hybridization experiments in situ displayd the exclusive expression of AODEF and AOGLOB at the primordia for inner tepals and stamens in wild type flowers. It appeared to remain during the early developmental stage, while the expression of AODEF in the mutant flowers rapidly disappeared in the early developmental stage. The transcripts for AOGLOA were not detected in the mutant flowers throughout the development.These results suggest that the lowered expression of AOGLOA causes a decline of the expression of AODEF and AOGLOB genes, and that the inability of B function genes leads to the phenotype found in an asparagus 'Gold Schatz' homeotic mutant.