Identification and pyramiding of QTLs for cold tolerance at the bud bursting and the seedling stages by use of single segment substitution lines in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

Cold stress is one of the main constraints in rice production, and damage from cold can occur at different developmental stages in rice. Understanding the genetic basis of cold tolerance is the key for breeding cold-tolerant variety. In this study, we used single segment substitution lines (SSSLs) derived from a cross between cold-tolerant japonica variety “Nan-yang-zhan” and a popular indica variety “Hua-jing-xian 74” to detect and pyramid QTLs for cold tolerance at the bud bursting and the seedling stages. Evaluation of cold tolerance of these SSSLs and their recurrent parent helped identify two cold-tolerant QTLs (qCTBB-5 and qCTBB-6) at the bud bursting stage and two cold-tolerant QTLs (qCTS-6 and qCTS-12) at the seedling stage. The SSSLs carrying these QTLs showed stronger cold tolerance than their recurrent parent HJX74 did in three independent experiments. The qCTBB-6 and qCTS-6 were mapped to the same chromosomal region. QTL pyramiding was performed by intercrossing of SSSLs carrying the respective QTLs for cold tolerance at the bud bursting stage and the seedling stage and marker-assisted selection (MAS). The selected pyramiding line SC1-1 with different cold-tolerant QTLs showed cumulative effects on cold tolerance. Our results suggest that different genes (QTLs) control cold tolerance at bud bursting and seedling stages, and pyramiding of stable expression QTLs for cold tolerance at different developmental stages through MAS is a good strategy to prevent cold damage in rice.     

Multiple loss-of-function 5-O-glucosyltransferase alleles revealed in Vitis vinifera,but not in other Vitis species

Key message

Wild and loss-of-function alleles of the 5 - O - glucosyltransferase gene responsible for synthesis of diglucoside anthocyanins in Vitis were characterized. The information aids marker development for tracking this gene in grape breeding.

Abstract

Anthocyanins in red grapes are present in two glycosylation states: monoglucoside (3-O-glucoside) and diglucoside (3, 5-di-O-glucoside). While monoglucoside anthocyanins are present in all pigmented grapes, diglucoside anthocyanins are rarely found in the cultivated grape species Vitis vinifera. Biochemically 3-O-glucoside anthocyanins can be converted into 3,5-di-O-glucoside anthocyanins by a 5-O-glucosyltransferase. In this study, we surveyed allelic variation of the 5-O-glucosyltransferase gene (5GT) in 70 V. vinifera ssp. vinifera cultivars, 52 V. vinifera ssp. sylvestris accessions, 23 Vitis hybrid grapes, and 22 accessions of seven other Vitis species. Eighteen 5GT alleles with apparent loss-of-function mutations, including seven premature stop codon mutations and six frameshift indel mutations, were discovered in V. vinifera, but not in the other Vitis species. A total of 36 5GT alleles without apparent loss-of-function mutations (W-type) were identified. These W-type alleles were predominantly present in wild Vitis species, although a few of them were also found in some V. vinifera accessions. We further evaluated some of these 5GT alleles in producing diglucoside anthocyanins by analyzing the content of diglucoside anthocyanins in a set of representative V. vinifera cultivars. Through haplotype network analysis we revealed that V. vinifera ssp. vinifera and its wild progenitor V. vinifera ssp. sylvestris shared many loss-of-function 5GT alleles and extensive divergence of the 5GT alleles was evident within V. vinifera. This work advances our understanding of the genetic diversity of 5GT and provides a molecular basis for future marker-assisted selection for improving this important wine quality trait.     

Ultrastructural changes and dynamic expressions of FAD7, Cu/Zn-SOD,and Mn-SOD in Neosinocalamus affinis under cold stress

As one of the fast-growing species, bamboo plays an important role in ecological stability and wood processing industry. However, low temperature limitation is the basic problem for the cultivation and introduction of bamboo. In this study, the symptoms of cold stress influence on the native bamboo (Neosinocalamus affinis (Rendle) Keng f.) and hybrid bamboo (Bambusa pervariabilis × Dendrocalamopsis grandis) were observed under transmission electron microscope, and the dynamic responses of FAD7, Cu/Zn-SOD, and Mn-SOD genes to cold stress were identified in bamboo by real-time quantitative RT-PCR. Observation by electron microscopy indicated that bamboo is one of the most chilling-sensitive species with severe ultrastructural injury induced by chilling, but the native bamboo (N. affinis) is more cold-tolerant compared with the hybrid bamboo. Results obtained by real-time quantitative RT-PCR analysis revealed that FAD7, Cu/Zn-SOD, and Mn-SOD were all cold-inducible genes in N. affinis. In addition, dynamic response patterns of N. affinis Cu/Zn-SOD and Mn-SOD under cold stress were similar. This work is a fundamental research of hardiness physiology of bamboo and may contribute to the breeding program on obtaining transgenic bamboo species.     

Overexpression of VaCBF4, a Transcription Factor from Vitis amurensis, Improves Cold Tolerance Accompanying Increased Resistance to Drought and Salinity in Arabidopsis

Environmental stress has a great impact on fruit yield and quality in grapes. Understanding mechanisms underlying stress tolerance in plants is useful for grape breeding. Here, a CBF gene, designated VaCBF4, was identified in V. amurensis. The expression of VaCBF4 was induced by several abiotic stresses, including cold, exogenous abscisic acid (ABA), drought, salinity, and cold-drought conditions. A yeast one-hybrid assay demonstrated that VaCBF4 protein could bind to a conserved DRE cis-element, which contains the core sequence ACCGAC and regulates cold- and dehydration-responsive. Transgenic Arabidopsis seedlings overexpressing VaCBF4 showed enhanced tolerance to cold, drought, and salinity when compared with wild-type controls. LT₅₀, a chilling temperature required to cause 50 % electrolyte leakage in leaves, was 4 °C lower in transgenic Arabidopsis lines than that in non-cold-acclimated wild-type seedlings. Moreover, two stress-responsive genes, AtRD29A and AtCOR47, also showed higher levels of expression in the transgenic lines than in wild-type seedlings under normal growth condition. Taken together, all these results clearly indicate that VaCBF4 is involved in the response to abiotic stresses, and it may be a good candidate gene for genetic improvement to develop stress-tolerant varieties in grapes.