First brassinosteroid-based dwarf mutant discovered and characterized in grapevine.

Area of Science:

• Plant Genetics
• Molecular Biology
• Agricultural Science

Background:

• Dwarfism in grapevines can impact vine architecture and fruit yield.
• Understanding the genetic basis of dwarfism is crucial for grapevine breeding programs.

Purpose of the Study:

• To identify the genetic factors controlling naturally occurring dwarfism in grapevine mutant lines.
• To elucidate the molecular mechanisms underlying grapevine dwarfism and its effect on vine architecture.

Main Methods:

• Trait-segregation and marker-trait association analyses were performed.
• Bulked RNA-sequencing (RNA-seq) and fine mapping were employed to identify candidate genes.
• CRISPR/Cas9 gene editing was used to validate gene function.

Main Results:

• A major locus associated with dwarfism was identified on Chromosome 14.
• VviBR6OX1, a gene encoding a cytochrome P450 enzyme in brassinosteroid synthesis, was identified as a key candidate gene.
• Two in-frame deletions in VviBR6OX1 were found, with a 9-bp deletion strongly linked to the dwarf phenotype. CRISPR/Cas9 editing confirmed VviBR6OX1's role in vine architecture.
• Simultaneous editing of VviBR6OX2 resulted in an extreme compact dwarf phenotype.

Conclusions:

• Mutations in VviBR6OX1 and VviBR6OX2 are responsible for dwarfism and compact vine architecture in grapevines.
• Brassinosteroid (BR) signaling plays a critical role in regulating grapevine growth and architecture.
• This research provides valuable genetic insights for developing improved grapevine varieties with desired architectural traits.