Abstract
We investigated the ability of RNA interference (RNAi) directed against two co-orthologs of AGAMOUS (AG) from Malus domestica (domestic apple, MdAG) to reduce the risks of invasiveness and provide genetic containment of transgenes, while also promoting the attractiveness of flowers for ornamental usage. Suppression of two MdAG-like genes, MdMADS15 and MdMADS22, led to the production of trees with highly showy, polypetalous flowers. These “double-flowers” had strongly reduced expression of both MdAG-like genes. Members of the two other clades within in the MdAG subfamily showed mild to moderate differences in gene expression, or were unchanged, with the level of suppression approximately proportional to the level of sequence identity between the gene analyzed and the RNAi fragment. The double-flowers also exhibited reduced male and female fertility, had few viable pollen grains, a decreased number of stigmas, and produced few viable seeds after cross-pollination. Despite these floral alterations, RNAi-AG trees with double-flowers set full-sized fruit. Suppression or mutation of apple AG-like genes appears to be a promising method for combining genetic containment with improved floral attractiveness.
Highlights
Many ornamental and fruit tree species are grown outside of their native range as exotics, and have the potential to become invasive
MdMADS15 and MdMADS22 are highly similar to AG genes from several species (S1 Fig)
This phenotype was consistent with reduction of AG function; petaloid anthers were previously reported as a result of RNA interference (RNAi) of AG in Arabidopsis thaliana (A. thaliana) as well as tomato (Solanum lycopersicum), and these phenotypic changes were milder than the strong phenotype of ag-1 allele in A. thaliana [14, 15]
Summary
Many ornamental and fruit tree species are grown outside of their native range as exotics, and have the potential to become invasive. Sterile trees would have the benefits of reduced invasiveness, decreased production of allergenic pollen, and mitigation of unwanted gene flow [2]. Existing ablation-based GE methods have led to the successful creation of male-sterile pines, eucalypts, and poplars [4, 5]. Some popular ornamental varieties of trees, such as Bradford pear, are both bisexual and invasive [7]. GE technology could be used to create bisexually sterile versions of such trees, greatly reducing their potential for spread via sexual propagules, while keeping their basic vegetative traits and adaptations intact
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