Microvine as a model system for functional gene characterization in grapevine berries

Abstract

Despite significant progress in grapevine research, conducting functional genetic studies at the berry level remains challenging due to thespecies’ physiological and developmental limitations, including its perennial growth habit, large plant size, and long juvenile phase. In this context, microvine offers a valuable alternative model by combining a dwarf stature, continuous flowering, and an accelerated reproductive cycle that enable rapid berry development under controlled conditions. Therefore, the microvine mutant represents a powerful platform for fruit-focused functional genomics and targeted genetic manipulation in grapevine.

In our group, inflorescences from microvine fruit cuttings grown under controlled environmental conditions were used to produce inflorescences for isolating stamens with immature pollen, which were then cultured in-vitro to induce embryogenic calli. Two distinct media, MSII and PIV, were tested for embryogenic callus induction, resulting in callus formation efficiencies of 2.8 % and 0.48 %, respectively. The embryogenic calli were subsequently subjected to in vitro regeneration assays using two different culture media, NN and X6, achieving whole-plant regeneration efficiencies of 42.35 % and 13.75 %, respectively. Regenerated plants were monitored for vegetative growth and development and were later successfully acclimated.

Through Agrobacterium-mediated stable transformation, we are currently using the microvine platform for the functional characterization of key genes involved in grape berry development and ripening. The VvAGL11 gene, a major regulator of seed development, is being knocked out to induce a seed abortion–like phenotype, providing a controlled system to investigate stenospermocarpy mechanisms. Meanwhile, for the functional analysis of transcription factors VvNAC33, VvNAC60, and VvNAC18, recognized as key regulators of grape berry ripening, stable overexpression lines are being regenerated. Additional constructs, based on serial deletions of the NAC geneand promoter regions, are being developed to finely modulate their expression during berry ripening.

Overall, this work establishes microvine as a versatile and efficient platform for fruit-focused functional gene analysis in grapevine, enabling the dissection of molecular networks involved in berry development and maturation and supporting future strategies for genetic improvement in grapevine.