Abstract:
Fresh fruit dominates New Zealand’s (NZ) horticultural exports, and the kiwifruit industry has
made a significant contribution in past years. Kiwifruit and kiwiberry are economically essential
fruit crops that belong to the genus Actinidia. Kiwifruit is NZ’s fastest growing horticultural
export, forecasting more growth in the next two years. Kiwiberry has been added recently to the
export list and is enjoying growing consumer acceptance worldwide. However, fruit production
will face significant challenges with climate change, most notably, the loss of winter chilling needs
for flowering. Additionally, kiwiberry breeders are looking at fast-breeding tracks by escaping
long juvenile phases to develop high-quality varieties.
The PEBP genes regulate flowering and architecture in various plant species, including kiwifruit.
This thesis investigates the role of selected PEBP candidates, AcBFT2 in kiwifruit winter
dormancy and AaCEN/AaCEN4 in kiwiberry flowering. In the first experiment, CRISPR/Cas9 was
used to target the AcBFT2 gene in the wild-type and fast-flowering backgrounds. The editing
construct was designed to preferentially target AcBFT2, whose expression is elevated in dormant
buds. The Acbft2-edited lines displayed an ever-growing phenotype, while control plants
established winter dormancy. RNA-seq transcriptomic analyses were conducted using buds from
the Acbft2-edited and control lines to study the AcBFT2 molecular action. The transcriptomic
comparison revealed that the Acbft2 mutation was largely attributed to reducing growth cessation
and bud set, while AcBFT2 expression enhanced the stress response to maintain dormancy. Double
mutant of Acbft2-Accen4 support that Acbft2 mutation did not affect flowering time. Overall, it
suggested that AcBFT2 knockout lines are less sensitive to conditions that establish winter
dormancy and maintain regular growth and development by making ever-growing phenotypes and
no adverse effect on flowering.
Secondly, the same technology was utilised to edit AaCEN/AaCEN4 in the kiwiberry to induce
early maturity. The resultant dwarf lines with rapid and precocious flowering and fruit
development secure the accelerated breeding and development of new varieties. The results
presented in this thesis contribute to fast breeding and gene editing to improve Actinidia spp. and
are better suited for the changing climate and needs.