Unlocking the genetic secrets of grape seedlessness

VviAGL11 gene sequencing and expression analysis. Credit: Horticultural Research

Seedlessness in table grapes is an important breeding target, often as a result of stenospermocarpy, which is associated with the Thompson Seedless grape variety. Advances in genetic research have identified the VviAGL11 gene, one of the MADS-box transcription factor family, as important in this process.

This gene, related to seed development, has a specific mutation (Arg197Leu) strongly associated with seedlessness. Despite significant progress in understanding the genetic aspects of stenospermocarpy, the functional mechanisms of VviAGL11 in inducing seedlessness in grapes remain unclear, presenting a major target for ongoing research.

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

In this study, the entire gene sequence of VviAGL11 was first isolated and sequenced from nine grapevine varieties. Researchers identified three main CDSs: seeded (wild type, WT), seedless (mutated, MUT), and hybrid (HYB) and two main types of promoters (i) seeded (wild type promoter, WTpro) and seedless (mutated promoter, MUTpro ).

Notably, a full association was found between WT promoter and WT CDS, and MUT promoter with MUT or HYB CDS. Expression level analyzes revealed the highest overall VviAGL11 expression in Pizzutello Bianco, a variety with the HYB allele. In contrast, Thompson Seedless showed the lowest total expression.

VviAGL11 has been shown to regulate its own transcription in a promoter-CDS-specific manner. GUS fluorimetric assays showed that both WT and MUT CDSs could activate the WT promoter, while all CDSs activated the MUT promoter, with the HYB CDS showing the strongest induction.

Transcriptomic assays of ovules and seeds identified differentially-expressed genes (DEGs) between seeded (SD) and seedless (SL) varieties at different developmental stages, identifying 2,490 upregulated and 851 downregulated genes in seed development stage S3.

The upregulated genes were shown to be mainly involved in protein metabolism and remodeling, nucleic acid metabolism, and transport. In contrast, the downregulated genes do not specifically represent any functional categories and mainly involve “signal pathways” and “stress responses.”

Finally, to identify VviAGL11 target genes, a multi-VviAGL11 co-expression analysis was performed, which led to the identification of a methyl jasmonate esterase, an indole-3-acetate beta-glucosyltransferase, and an isoflavone reductase as a top target candidate. In vivo experiments further confirmed the role of VviAGL11 in regulating these genes, showing its significant influence on seed development and the seedless behavior of grapes.

In conclusion, this study of VviAGL11 in grapevines revealed three distinct promoter-CDS combinations that influence gene expression and are seedless. By examining VviAGL11 alleles, the researchers showed that VviAGL11 activates itself in specific combinations and identified key target genes involved in hormone signaling and secondary metabolism.

These findings indicate that the wild-type VviAGL11 CDS activates important genes in seed development. The study highlights a new regulatory mechanism linking VviAGL11 seedless haplotypes, suggesting potential applications in grapevine breeding for seedlessness and fruit size optimization.

More information:
Alessandra Amato et al, VviAGL11 self-regulates and targets hormone-related genes and secondary metabolism during seed development, Horticultural Research (2022). DOI: 10.1093/hr/uhac133

Provided by Plant Phenomics

Citation: Unlocking the genetic secrets of grape seedlessness (2023, December 21) retrieved 21 December 2023 from https://phys.org/news/2023-12-genetic-secrets-grape-seedlessness.html

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