New strategy of "two in one" rapid breeding

Xu Cao's research group from the Institute of Genetics and Developmental Biology, Chinese Academy of Sciences published a paper titled "A two-in-one breeding strategy boosts rapid utilization of wild species and elite cultivars" online in Plant Biotechnology. This study reports a new "two-in-one" rapid breeding strategy, which combines the new de novo domestication breeding method and the classic hybrid breeding technology to complement each other's strengths, and realize the rapid introduction of stress tolerance traits and the development of diversified planting models in tomato. One-click creation provides new ideas for efficient and rapid utilization of excellent wild resources and cultivated germplasm, and cultivation of environment-adaptive crops and crops with diverse planting patterns.

Global climate change has led to frequent occurrence of extreme weather, threatening the development of modern agriculture and national food security. After long-term artificial breeding, most crops have achieved the aggregation of high-yield and high-quality traits, but the genetic diversity has decreased, and the breeding of complex traits has encountered genetic bottlenecks, making it difficult to adapt to future climate changes and frequent extreme weather. The development of gene editing technology has made rapid and precise breeding possible, but the rapid creation of complex agronomic traits determined by multiple quantitative trait loci remains extremely challenging, such as environmental adaptation and tolerance traits. In particular, the lack of efficient plant gene editing tools in terms of gene "knock-in" or "knock-up" makes it difficult to create many complex traits through gene editing. Wild plants have undergone long-term natural selection and environmental adaptive evolution, and have natural environmental adaptation and stress tolerance traits; while modern cultivated species have excellent yield and quality traits after long-term artificial breeding, and the "pearl and bare" of the two is a prominent feature of future crops. Traditional breeding can introgress the stress tolerance traits of wild species into cultivated species through hybridization, however, this process of gene introgression is time-consuming and laborious due to multiple factors such as reproductive barriers of wild species, huge growth habit differences, and labor and time costs of artificial emasculation of cultivated species.

Xu Cao's research group draws on the new method of domestication and breeding from scratch and the classic technology of cross-breeding to complement each other's advantages, and propose a new "two-in-one" rapid breeding strategy. This strategy quickly creates male sterile lines in tomato cultivars through gene editing technology, reducing labor costs for hybridization; de novo domestication of wild species with excellent stress tolerance traits reduces the time cost of trait introduction, and realizes wild species and the "double reduction" of the integration of excellent traits of cultivars and the efficient use of germplasm resources have accelerated the process of stress tolerance breeding.

In this study, Ailsa Craig (AC), a classical cultivated tomato variety, was selected as the parental material to create a male sterile material using CRISPR/Cas9 to knock out the isolicin synthase encoding gene SlLAP3, which is specifically expressed at the microspore stage in tomato, and it was confirmed that the agronomic characteristics such as growth and development and yield quality of this material were affected in addition to sterility. In order to obtain excellent stress tolerance traits, the wild currant tomato Solanum pimpinellifolium (S. pimp) originating from the severe saline-alkali land of the Peruvian seashore was selected as a donor in this study, and the de novo domestication gene modules of tomato flowering and plant types identified earlier in the laboratory, SELF-PRUNING 5G (SP5G) and SELF-PRUNING (SP) genes, that are insensitive to photoperiod, and have both synchronous fruit ripening and compact plant types, were rapidly created using a multi-target genome editing system, which overcomes the differences in growth habits of wild tomatoes and maintains their excellent traits of severe saline-alkali tolerance and high disease resistance. De novo domesticated S. pimp lines were crossed with AC male sterile lines, and F1 plants presented an intermediate phenotype compared with the parents. Plants with both maternal yield and quality traits, male tolerance to severe saline-alkali and high disease resistance traits were obtained in the F2 segregating population. At the same time, the F2 segregating population can also isolate and obtain lines containing sp, sp5g, sp sp5g mutation combinations in addition to the above traits, which present different plant types and can be suitable for various planting modes such as open field cultivation, greenhouse cultivation and plant factory cultivation, respectively. Through the integration of de novo domestication and rapid creation of male sterile lines, the "double reduction" of manpower and time costs in the mining and utilization of excellent wild and cultivated species resources and germplasm innovation was realized, while the diversified separation of domesticated gene modules achieved the "increase" of planting methods.

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