The control of prickle formation in Rubus

Area of Science:

• Plant genetics
• Agricultural science
• Molecular biology

Background:

• Prickles on blackberry and raspberry canes pose challenges for cultivation and harvesting, increasing labor costs.
• Developing prickleless cultivars has been difficult due to the recessive nature of the trait and its linkage with undesirable agronomic characteristics.
• Traditional breeding programs have relied on recessive mutants at the S locus for over a century to produce prickleless varieties.

Purpose of the Study:

• To identify the genetic basis of the prickleless trait in blackberry and red raspberry.
• To investigate the role of the WOX1 gene in prickle development.
• To explore the potential of gene editing for developing improved, prickleless cultivars.

Main Methods:

• Integrated genome-wide association, bulked segregant analysis, and identity-by-descent analyses were used to map the S locus.
• Genome sequencing of the 'Burbank Thornless' blackberry variety was performed.
• Gene editing (CRISPR-Cas9) was employed to knock out the WOX1 gene in an elite prickled blackberry line.

Main Results:

• Independent loss-of-function mutations in the WOX1 gene were identified as the cause of the prickleless S locus in both species.
• Knockout of WOX1 in a commercial blackberry line resulted in prickleless plants lacking glandular trichomes.
• Edited plants maintained other desirable agronomic traits, indicating WOX1's specific role.

Conclusions:

• WOX1 is a key genetic factor controlling prickle development and glandular trichome formation in raspberries and blackberries.
• Gene editing of WOX1 provides a precise and efficient strategy for developing prickleless cultivars directly from elite varieties.
• This approach can accelerate breeding cycles, leading to safer and easier-to-handle berry crops for growers.