Abstract
BackgroundThe homeobox transcription factor has a diversity of functions during plant growth and development process. Previous transcriptome analyses of seed development in grape hybrids suggested that specific homeodomain transcription factors are involved in seed development in seedless cultivars. However, the molecular mechanism of homeobox gene regulating seed development in grape is rarely reported.ResultsHere, we report that the grapevine VvHB58 gene, encoding a homeodomain-leucine zipper (HD-Zip I) transcription factor, participates in regulating fruit size and seed number. The VvHB58 gene was differentially expressed during seed development between seedless and seeded cultivars. Subcellular localization assays revealed that the VvHB58 protein was located in the nucleus. Transgenic expression of VvHB58 in tomato led to loss of apical dominance, a reduction in fruit pericarp expansion, reduced fruit size and seed number, and larger endosperm cells. Analysis of the cytosine methylation levels within the VvHB58 promoter indicated that the differential expression during seed development between seedless and seeded grapes may be caused by different transcriptional regulatory mechanisms rather than promoter DNA methylation. Measurements of five classic endogenous hormones and expression analysis of hormone-related genes between VvHB58 transgenic and nontransgenic control plants showed that expression of VvHB58 resulted in significant changes in auxin, gibberellin and ethylene signaling pathways. Additionally, several DNA methylation-related genes were expressed differentially during seed development stages in seedless and seeded grapes, suggesting changes in methylation levels during seed development may be associated with seed abortion.ConclusionVvHB58 has a potential function in regulating fruit and seed development by impacting multiple hormonal pathways. These results expand understanding of homeodomain transcription factors and potential regulatory mechanism of seed development in grapevine, and provided insights into molecular breeding for grapes.
Highlights
The homeobox transcription factor has a diversity of functions during plant growth and development process
In order to further explore the expression pattern of VvHB58 in seed development stages, we selected 12 seed development stages to evaluate the expression of VvHB58 in 4-year-old ‘Thompson Seedless’ and ‘Red Globe’ (Because ‘Thompson Seedless’ and ‘Red Globe’ are representative cultivars of seedless grapes and seeded grapes respectively, the two cultivars were further considered for expression analysis in the following year)
During seed development between 21 to 48 days after full bloom (DAF), expression of VvHB58 was high in ‘Thompson Seedless’, but relatively low in ‘Red Globe’ (Fig. 1b), suggesting that VvHB58 may participate in seed development of seedless grapes
Summary
The homeobox transcription factor has a diversity of functions during plant growth and development process. The molecular mechanism of homeobox gene regulating seed development in grape is rarely reported. Many differentially expressed genes in seedless and seeded grapes have been identified [1, 11]. These genes are mainly involved in seed coat differentiation, hormone homeostasis, epigenetic regulation, reproductive development, cell cycle and primary and secondary metabolism [1, 11]. Because many of these genes may have pleiotropic effects, it is difficult to estimate their specific molecular contribution to seed and fruit development. The lack of VviAGL11 expression activation precludes seed coat differentiation and triggers Salicylic acid production along with the overexpression of NAC, Homeobox and WRKY TFs, and eventually leads to endosperm degeneration and embryo developmental arrest [1]
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