Abstract
Winter hardiness is an important trait for grapevine breeders and producers, so identification of the regulatory mechanisms involved in cold acclimation is of great potential value. The work presented here involves the identification of two grapevine ICE gene homologs, VaICE1 and VaICE2, from an extremely cold-tolerant accession of Chinese wild-growing Vitis amurnensis, which are phylogenetically related to other plant ICE1 genes. These two structurally different ICE proteins contain previously reported ICE-specific amino acid motifs, the bHLH-ZIP domain and the S-rich motif. Expression analysis revealed that VaICE1 is constitutively expressed but affected by cold stress, unlike VaICE2 that shows not such changed expression as a consequence of cold treatment. Both genes serve as transcription factors, potentiating the transactivation activities in yeasts and the corresponding proteins localized to the nucleus following transient expression in onion epidermal cells. Overexpression of either VaICE1 or VaICE2 in Arabidopsis increase freezing tolerance in nonacclimated plants. Moreover, we show that they result in multiple biochemical changes that were associated with cold acclimation: VaICE1/2-overexpressing plants had evaluated levels of proline, reduced contents of malondialdehyde (MDA) and decreased levels of electrolyte leakage. The expression of downstream cold responsive genes of CBF1, COR15A, and COR47 were significantly induced in Arabidopsis transgenically overexpressing VaICE1 or VaICE2 upon cold stress. VaICE2, but not VaICE1 overexpression induced KIN1 expression under cold-acclimation conditions. Our results suggest that VaICE1 and VaICE2 act as key regulators at an early step in the transcriptional cascade controlling freezing tolerance, and modulate the expression levels of various low-temperature associated genes involved in the C-repeat binding factor (CBF) pathway.
Highlights
Grapevine (Vitis L.) is one of the most widely cultivated fruit crops worldwide, and is of great economic importance
Analysis of structural properties revealed that the predicted VaICE1 or VaICE2 protein possesses the typical features of ICE proteins, including a serine-rich region (S-rich), a basic helix-loop-helix domain, an ICE-specific domain [38], a zipper region (ZIP) and an ACT_UUT-ACR-like domain (Fig. 1B)
An interPro scan suggested that both proteins belong to the MYC-like basic helix-loop-helix (bHLH) family of transcription factors, and in support of this, they contain nuclear location signals (NLSs) at position 12– 46 aa for VaICE1 and 339–362 aa for VaICE2 (Fig. 1B)
Summary
Grapevine (Vitis L.) is one of the most widely cultivated fruit crops worldwide, and is of great economic importance. The grapevine cultivars that currently dominate the market in terms of acreage and production of premium wines are derived from the species Vitis vinifera, but they tend to be very sensitive to low winter temperatures [6]. Enhancing low temperature tolerance of grapevine is of great practical importance. In this context, the current study focuses on Vitis amurensis Rupr., a wild grape species that is native to China and is extremely coldtolerant [7], withstanding freezing temperature as low as 240uC [8]. Understanding the mechanisms underlying tolerance and adaptation to cold stress could potentially lead to the development of new strategies for improving the yield of cold sensitive agronomic plants and expanding the geographic areas of production
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