GENETIC ENGINEERING OF THE SELF-INCOMPATIBILITY MECHANISM IN ‘ELSTAR’ APPLE LEADS TO DISTINCT LEVELS OF SELF-FERTILITY

The apple cultivar ‘Elstar’ (S-RNase genotype S₃S₅) was transformed with T-DNA constructs containing the S₃-RNase cDNA in anti-sense orientation.
The resultant transgenic lines were screened for their ability to set fruit following self-pollination under controlled greenhouse conditions and results compared to previous work on lines containing a full length sense S₃-cDNA T-DNA construct.
Detailed molecular and physiological analysis identified 12 lines with a stable, altered SI-phenotype.
In all 12 lines complete S₃ S-RNase gene silencing, and partial S₅ S-RNase silencing significantly modified the self-incompatibility behaviour of the plant, leading to either intermediate or complete self-fertility.
Interestingly, the intermediate self-fertile phenotype appeared to be due to a slower growth rate of ‘self’ pollen tubes and was only observed in a subset of lines that were generated using the 3’ end of the S₃-cDNA in anti-sense orientation.
For as yet unknown reasons, the SI-reproductive barrier remains partially active in this subset of lines.
We also demonstrated that transgenic S-silenced lines can still display fruit set in the absence of any active pollination vector.
Overall, our data demonstrate that S-RNase-silenced apple trees displaying a range of self-fertile phenotypes represent a powerful tool to help understand the biological implications of the removal of the GSI reproductive barrier and the possible impact of this technology on hard fruit production.

I Workshop on Floral Biology and S-Incompatibility in Fruit Species

R.S.G. Dreesen, M.W. Davey, J. Keulemans

gametophytic self-incompatibility, S-RNase, fruit set, pollen tube growth, seed set, Malus × domestica

https://doi.org/10.17660/ActaHortic.2012.967.18