葡萄芽变机制研究进展及应用

Advances in research on bud mutantation mechanism in grape

芽变作为一种重要的果树育种手段,受到研究者和育种家的高度重视。环境条件等因素是诱导体细胞突变形成芽变的主要原因,L1、L2不同细胞层的变异引起葡萄不同性状发生改变。近年来,随着高通量测序技术的快速发展,研究者开发出不同的分子标记方法对葡萄芽变进行鉴定,同时葡萄芽变的变异机制也有了较为深入的研究。笔者重点从葡萄的花序和果穗、果实颜色、果型、成熟期、果实无核、植株结构及倍性这些性状的变异机制进行阐述,旨在为葡萄芽变育种提供理论参考。

Grape(Vitis L.) is one of the oldest and economically important fruit crops in the world., and grape fruits are mainly used for fresh consuming(30%), wine making(68%), raisins and juice processing(2%). The important grape breeding objectives are early maturity, large fruit, seedless fruit, and rich flavor. There are various grape breeding methods, including hybrid breeding, mutation breeding and biotechnology-based breeding. Many new mutant varieties with novel traits have been generated through bud mutant selection. Therefore, mutant selection is one of the most important breeding methods to obtain new cultivars with superior traits in grape. This article focuses on the research progress in the identification of mutants and exploration the mechanism of the bud mutants in grape. Somatic mutants mainly occur in the cell layer of the apical meristem in grape. The shoot apical meristem(SAM) is composed of two layers: the outer meristem layer(L1), and the second meristem layer(L2). The epidermis of leaves is derived from the L1 layer, L2 layer participates in the regulation of internal organization.Changes of L1 and L2 layer would result in bud mutantation. The prerequisite of bud mutantation is the change of DNA sequence. According to the current research on DNA sequence changes, a SNP could alter the expression of a gene, leading to a specific phenotype of cells. DNA methylation is also an important cause for epigenetics, which alters gene expression without changing the sequence of DNA. The transposon insertions could provide a convenient method to generate tagged null mutants that could be easily identified on a genome-wide scale and are likely to reflect phenotypes arising from common indels and point mutants that would result in loss-of-function. The change of DNA sequence would cause bud mutantation, and at the same time cause the variation of traits. The phenotypic variation might be caused by both genetic and environmental components. The identification of bud mutantation through morphological characteristics could not achieve a precise result. Thus, various DNA molecular marker technologies based on the DNA sequences, Randomly Amplified Polymorphic DNA(RAPD), InterPrimer Binding Site(IPBS), Inter-Simple Sequence Repeat(ISSR), Simple Sequence Repeat(SSR), Sequence Related Amplified Polymorphism(SRAP) have been used to identify sports and their original plants. At the same time, studies have demonstrated that different traits of bud mutant are regulated by different genes, for example, VvMYBA1 and VvMYBA2 transcription factors, could regulate the color of the grape berry, in Vitis vinifera. The glycosylation catalyzed by UDP-glucose, anthocyanidin, flavonoid glucosyltransferase(UFGT) is the key step of anthocyanin biosynthesis. The main reason for the participation of VvmybA1 in the regulation is the insertion of a transposon Gret1 in the coding region of its gene, thereby regulating the expression of genes and participating in the synthesis of anthocyanins, leading to hindering the synthesis of anthocyanins and causing color variations. In the inflorescence and ear variation, the homologous factors MADS-box 1, 2 and 3 of the Arabidopsis floral genes AG, SEP and AGL13 alter their expression patterns during flower development and play a decisive role. The VvTFL1 A gene, a secondary transposon Hatvine1-rrm is inserted in the promoter region to affect the inflorescence development at an early stage. Fruit ripening is a complex process involving many highly coordinated physiological and biochemical changes. It is found to be involved in the regulation of ethylene and growth during the ripening period. Abnormal expression of the berry and cytokinin genes would delay or advance the fruit ripening period. For example, the level of reactive oxygen species in the bud mutant is always higher than that of the original plant. The abnormal expression of the VvMADS9 gene would be the main cause of abnormal berry morphology in the fruit type variation;The VvAGL11 gene would be the main candidate gene for seedless fruits. With the development of high-throughput technology, it is believed that the mutation mechanism of sports would be more clearer.