Researchers Identify Grapevine Dwarf Gene

Researchers have identified the first grapevine dwarf mutant tied to brassinosteroid biosynthesis, a finding that could help breeders develop vines better suited to dense planting and mechanized farming.

The study, published Monday in Theoretical and Applied Genetics, traced the trait to VviBR6OX1, a gene on chromosome 14 that helps make brassinosteroids, a class of plant hormones that regulate growth. The team also used CRISPR/Cas9 to recreate the dwarf phenotype in grapevine, confirming the gene’s role in controlling vine architecture. When they edited a second related gene, VviBR6OX2, the plants became even more compact.

The work comes from Cornell University’s Grapevine Breeding and Genetics Program and focuses on a naturally occurring dwarf line found among progeny of PI 200569, also known as Yugoslav 5-24. The mutant vines had small dark green leaves, short petioles and short internodes. In greenhouse and field tests, the dwarf trait followed a recessive pattern and fit a 3-to-1 segregation ratio, suggesting control by a single locus.

To narrow down the cause, the researchers combined marker-trait association analysis with bulked RNA sequencing. They found a strong signal on chromosome 14 and then refined the candidate region to a 137-kilobase interval containing nine genes. One stood out: VIT_214s0083g01110, which encodes brassinosteroid-6-oxidase. In grapevine nomenclature, the gene is called VviBR6OX1.

The team found two in-frame deletions in the gene: one of 12 base pairs in exon 1 and another of 9 base pairs in exon 4. A survey of grape germplasm suggested that the 9-base-pair deletion was most likely responsible for the dwarf phenotype. The mutant vines carried both deletions, while taller vines mostly carried the wild-type sequence.

To test whether VviBR6OX1 was truly causal, the researchers used CRISPR/Cas9 to knock out the gene in Scarlet Royal, a table grape cultivar. The edited plants developed a similar dwarf form, with shorter shoots and reduced overall size. In some lines, simultaneous editing of VviBR6OX2 produced an even more compact plant.

The findings matter because grape production still depends heavily on hand labor for pruning, training and harvest. Smaller vines could make it easier to design cultivars that support higher-density planting and lower labor costs. The study adds brassinosteroid pathways to the list of genetic routes that breeders can use to shape vine growth, alongside earlier work on gibberellin-related dwarfing genes.

The authors said the discovery offers a new genetic resource for breeding grapes with modified architecture and other traits linked to brassinosteroid biology.