A GmAOX2b antisense gene suppresses growth and reproductive development in soybean (Glycine max L.)

Alternative oxidase (AOX) comprises the cyanide-resistant respiratory pathway in the inner mitochondrial membrane in plant cells. In eudicots, AOX is encoded by two gene types, AOX1 and AOX2. The analyses of a number of AOX mutants with altered levels of AOX expression have significantly improved our understanding of the roles of AOX in plants. All AOX mutants examined have been generated by manipulating the expression of AOX1-type, but not AOX2-type genes. In this study, GmAOX2b antisense mutants of soybean were examined with the aim of better defining the role of AOX2 in plant growth and development. Three soybean lines that were previously independently transformed with a GmAOX2b antisense construct were analyzed under benign growth conditions. AOX protein abundance in the leaves of approximately 50% of the transgenic plants examined was variously reduced compared to non-transgenic controls. The absence of a mutant that totally lacked AOX protein favors the notion that there is a threshold level of AOX protein expression that is essential to plant viability. The antisense plants of two of the three transformed lines consistently transmitted the antisense gene to subsequent generations in a non-Mendelian manner, implying compromised gametophyte viability in these lines. Reduced pod and seed set in the antisense plants of all three transformed lines indicates that AOX is important to plant fecundity. Repressed fecundity in the antisense plants may be due to at least two mechanisms: early ovule abortion and compromised photosynthetic performance. Reproductive potential of the antisense plants of all three transformed lines was compromised, as indicated by the reduction in the potential number of seeds per plant. The frequency of potential fertilization events was reduced by at least one-third in the antisense plants of all three transformed lines. Pistils of antisense plants contained a larger number of immature-sized embryo sacs compared to non-transgenic