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We report the characterization of VvIAA19, an auxin/indole-3-acetic acid (Aux/IAA) protein, in grapevine (Vitis vinifera L.). VvIAA19 was expressed abundantly in berries. VvIAA19 transcription was rapidly increased at pre-anthesis and then decreased during fruit set. Before véraison, however, VvIAA19 gene expression was upregulated again and maximum expression was maintained until the end of ripening. Exogenous IAA did not induce VvIAA19 expression in grape leaves, suggesting that VvIAA19 might be auxin-nonresponsive. The overexpression of VvIAA19 in Arabidopsis thaliana had a notable effect on plant growth. Although no morphological changes were observed, transgenic Arabidopsis plants overexpressing VvIAA19 exhibited faster growth, including root elongation and floral transition, than the control plant, suggesting that the constitutive expression of VvIAA19 protein resulted in increased growth rates without any detectable harm. Taken together, we conclude that grape Aux/IAA19 protein is likely to play a crucial role as a plant growth regulator.

We report the characterization of VvIAA9, an auxin/indole-3-acetic acid (Aux/IAA) protein, in grapevine (Vitis vinifera L.). VvIAA9 was expressed abundantly in leaves and berries. VvIAA9 transcription was drastically upregulated from anthesis to onset of ripening (termed véraison), in which berry diameter rapidly increased. Treatment with exogenous IAA induced VvIAA9 expression in grape leaves, suggesting that VvIAA9 is an auxin-responsive Aux/IAA protein. The overexpression of VvIAA9 in Arabidopsis thaliana promoted plant growth, including rapid floral transition. However, no morphological differences were observed between the control plant and the VvIAA9-overexpressing plant. The overexpression of VvIAA9 in Arabidopsis plants rendered the plants hyposensitive to exogenous IAA. The exogenous IAA treatment did not induce VvIAA9-overexpressing Arabidopsis plant growth and expression of IAA-responsive HAT2. Taken together, we conclude that grape Aux/IAA9 protein is likely to play a crucial role as a plant growth regulator.

HSG1 (Heat shock-induced gene 1) is one of the high-temperature-induced proteins in grapevine. Sequence analysis has demonstrated that HSG1 is a grape Bcl-2-associated athanogene (BAG) that contains IQ and BAG domains in its sequence. HSG1 expression was not detected in leaves without heat treatment, while tendrils, stems, flowers, and berries expressed HSG1 even without heat treatment. By heat treatment at 45°C for 60 min, HSG1 expression was upregulated in both leaves and berries. HSG1-overexpressing Arabidopsis plant remained viable even after exposure to extremely high temperatures. Although no morphological changes were observed, the HSG1-overexpressing Arabidopsis plant exhibited faster floral transition than the control plant. Analysis of the transcription profile of HSG1-overexpressing seedling by cDNA microarray and quantitative RT-PCR demonstrated that the gene expression of the flowering promoter, CONSTANS (CO), in the photoperiod pathway was up-regulated in the seedling. Importantly, the overexpression of HSG1 increased CO expression by ~400% compared with the control seedling. Meanwhile, heat treatment upregulated grape CO expression in grape leaves. Our study provides the possibility that plant BAG protein may be related to the regulation of floral transition by activating CO expression in the photoperiod pathway.

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