Unraveling the genetic secret of seedless grapes

Seedlessness in table grapes is a key breeding goal, primarily due to the narrow fruiting nature associated with the Thompson seedless grape variety. Advances in genetic research have identified the VviAGL11 gene, a member of the MADS-box family of transcription factors, as critical in this process.

This gene is associated with seed development and has a specific mutation (Arg197Leu) that is closely associated with seedlessness. Despite significant progress in understanding the genetics of stenospermia, the functional mechanism by which VviAGL11 induces grape seedlessness remains unclear and is a major focus of ongoing research.

June 2022, Horticulture Research Published a research article titled “VviAGL11 self-regulates and targets hormone- and secondary metabolism-related genes during seed development.”

In this study, the complete gene sequence of VviAGL11 was first isolated and sequenced from nine grape varieties. The researchers identified three major CDS: seeded (wild type, WT), seedless (mutated, MUT), and hybrid (HYB) as well as two major types of promoters (i) seeded (wild-type promoter , WTpro) and seedless (mutated promoter, MUTpro)).

Notably, complete association was found between the WT promoter and WT CDS and between the MUT promoter and MUT or HYB CDS. Evaluation of expression levels showed that the variety Pizzutello Bianco with the HYB allele had the highest total expression of VviAGL11. In contrast, Thompson Seedless showed the lowest total expression.

VviAGL11 was shown to regulate its own transcription in a promoter-CDS-specific manner. GUS fluorescence assay showed that both WT and MUT CDS could activate the WT promoter, while all CDS activated the MUT promoter, among which HYB CDS showed the strongest induction effect.

Transcriptome analysis of ovules and seeds identified differentially expressed genes (DEGs) in seeded (SD) and seedless (SL) varieties at different developmental stages, with 2,490 up-regulated genes and 851 down-regulated genes identified at the seed development stage S3. .

The upregulated genes have been shown to be mainly involved in protein metabolism and modification, nucleic acid metabolism and transport. In contrast, down-regulated genes do not specifically represent any functional category and are mainly involved in “signaling pathways” and “stress response.”

Finally, to identify VviAGL11 target genes, multiple VviAGL11 co-expression analysis was performed, which identified jasmonate methylesterase, indole-3-acetate β-glucosyltransferase, and isoflavone reductase as the best candidate targets. In vivo experiments further confirmed the role of VviAGL11 in regulating these genes, demonstrating its significant impact on grapevine seed development and seedless traits.

In summary, this study of VviAGL11 in grapevine reveals three different promoter-CDS combinations that influence gene expression and seedlessness. By examining VviAGL11 alleles, the researchers demonstrated that VviAGL11 self-activates in specific combinations and identified key target genes involved in hormone signaling and secondary metabolism.

These findings indicate that wild-type VviAGL11 CDS activates key genes in seed development. This study highlights a novel regulatory mechanism linking the VviAGL11 haplotype to seedlessness, showing its potential application in grape seedless breeding and fruit size optimization.