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

‘Gold Schatz’芦笋的两个营养品系于1966年从东德引进日本，并通过无性繁殖保存在北海道大学。这些品系中的一株发育出小花被片呈绿色的花。未发现雄蕊，但与心皮相似的花器官在第3轮(雄蕊轮生)分化。这些不定心皮分化胚珠，包括胚囊和卵细胞。这些形态特征表明，‘Gold Schatz’品系可能是一个花器官发生的同源异型突变体，可能是由于B类MADS盒基因功能缺失所致。Southern杂交分析表明，当分别针对B类和C类MADS盒基因的DNA片段进行杂交时，野生型和突变体的DNA片段的带型没有差异。然后，通过Northern印迹分析检测了MADS-box基因(C类基因AOAG1和AOAG2，B类基因AODEF，AOGLOA和AOGLOB)在野生型和突变体花中的表达。因此，仅在野生型中检测到B功能基因的表达，或在突变花中几乎检测到B功能基因的表达。在两个品系的花中均检测到C功能基因的表达。原位杂交实验表明，AODEF和AOGLOB在野生型花的内花被和雄蕊原基上均有专一性表达。AODEF的表达在早期发育阶段保持不变，而在早期发育阶段AODEF的表达迅速消失。这些结果表明，AOGLOA基因的低表达导致AODEF和AOGLOB基因的表达下降，而B功能基因的缺失导致了芦笋‘Gold Schatz’同源异源突变体的表型。

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.