Abstract
Grapevine (Vitis vinifera L.) is a widely cultivated fruit crop whose growth and productivity are greatly affected by low temperatures. On the other hand, wild Vitis species represent valuable genetic resources of natural stress tolerance. We have isolated and characterized a MYB-like gene encoding a putative GARP-type transcription factor from Amur grape (V. amurensis) designated as VaAQUILO. AQUILO (AQ) is induced by cold in both V. amurensis and V. vinifera, and its overexpression results in significantly improved tolerance to cold both in transgenic Arabidopsis and in Amur grape calli. In Arabidopsis, the ectopic expression of VaAQ increased antioxidant enzyme activities and up-regulated reactive oxygen species- (ROS) scavenging-related genes. Comparative mRNA sequencing profiling of 35S:VaAQ Arabidopsis plants suggests that this transcription factor is related to phosphate homeostasis like their Arabidopsis closest homologues: AtHRS1 and AtHHO2. However, when a cold stress is imposed, AQ is tightly associated with the cold-responsive pathway and with the raffinose family oligosaccharides (RFOs), as observed by the up-regulation of galactinol synthase (GoLS) and raffinose synthase genes. Gene co-expression network (GCN) and cis-regulatory element (CRE) analyses in grapevine indicated AQ as potentially regulating VvGoLS genes. Increased RFO content was confirmed in both transgenic Arabidopsis and Amur grape calli overexpressing VaAQ. Taken together, our results imply that AQ improves cold tolerance through promoting the accumulation of osmoprotectants.
Highlights
Low temperature is a primary environmental factor that affects geographic distribution of plants and affecting agricultural plant growth and development, significantly constraining the productivity (Chinnusamy et al, 2007)
Direct evidence exists for the activities of some cold-regulated transcription factors not participating in the C-repeat binding factors (CBFs) cold response pathway, such as AtHOS9 (Zhu et al, 2004), OsMYB3R-2 (Dai et al, 2007), AtZAT12, AtMYB73, and AtWRKY33 (Jia et al, 2016), which suggests that transcriptional regulation plays a crucial role in cold responses as well as in the crosstalk between different signalling pathways (Fowler and Thomashow, 2002)
A phylogenetic tree based on the full-length protein sequences suggests that AQ shares the closest homology with AtHRS1, AtHHO2, and AtHHO3 (Fig. 1C), implying that AQ proteins may at least share the control of root traits, regulate genes governing phosphate homeostasis, and influence seed germination through abscisic acid (ABA) signalling like their homologues in Arabidopsis (Liu et al, 2009; Wu et al, 2012; Nagarajan et al, 2016)
Summary
Low temperature is a primary environmental factor that affects geographic distribution of plants and affecting agricultural plant growth and development, significantly constraining the productivity (Chinnusamy et al, 2007). C-repeat binding factors (CBFs; known as dehydration-responsive element-binding proteins or DREBs), act as central hubs in the cold signalling network and recognize a CRT/DRE cis-acting regulatory element present in the promoters of many cold-regulated (COR) genes (Vogel et al, 2005; Yamaguchi-Shinozaki and Shinozaki, 2005; Chinnusamy et al, 2007). Direct evidence exists for the activities of some cold-regulated transcription factors not participating in the CBF cold response pathway, such as AtHOS9 (Zhu et al, 2004), OsMYB3R-2 (Dai et al, 2007), AtZAT12, AtMYB73, and AtWRKY33 (Jia et al, 2016), which suggests that transcriptional regulation plays a crucial role in cold responses as well as in the crosstalk between different signalling pathways (Fowler and Thomashow, 2002)
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