Abstract
BackgroundCommon walnut (Juglans regia L.) is one of the top four most consumed nuts in the world due to its health benefits and pleasant taste. Despite its economic importance, the evolutionary history and genetic control of its adaptation and agronomic traits remain largely unexplored.ResultsWe report a comprehensive walnut genomic variation map based on whole-genome resequencing of 815 walnut accessions. Evolutionary analyses suggest that Chinese J. regia diverged from J. sigillata with extensive hybridizations after the split of the two species. In contrast to annual crops, the genetic diversity and heterozygous deleterious mutations of Chinese common walnut trees have continued to increase during the improvement process. Selective sweep analyses identify 902 genes uniquely selected in the improved common walnut compared to its progenitor population. Five major-effect loci are identified to be involved in walnut adaptations to temperature, precipitation, and altitude. Genome-wide association studies reveal 27 genomic loci responsible for 18 important agronomic traits, among which JrFAD2 and JrANR are the potentially major-effect causative genes controlling linoleic acid content and color of the endopleura of the nut, respectively.ConclusionsThe largest genomic resource for walnuts to date has been generated and explored in this study, unveiling their evolutionary history and cracking the genetic code for agronomic traits and environmental adaptation of this economically crucial crop tree.
Highlights
Common walnut (Juglans regia L.) is one of the top four most consumed nuts in the world due to its health benefits and pleasant taste
Based on the maximized marginal likelihood value estimated by fastSTRUCTURE [18], K = 4 was the optimal grouping number (Fig. 1a; Additional file 2: Fig. S2). At this K value, we found the J. regia (JR) accessions could be further divided into 3 main subgroups (JR1, JR2, and JR3), in which JR1 mainly consists of accessions from Middle and North China, JR2 accessions are mainly distributed in Northwest (Xinjiang) and Northeast (Liaoning) China, while the JR3 subgroup consists of accessions from Iran, Pakistan, and the Tibetan Plateau, China (Fig. 1a, b)
Based on the most comprehensive walnut genomic variation map to date, we found that Chinese J. regia likely diverged from J. sigillata with a genetic bottleneck
Summary
Common walnut (Juglans regia L.) is one of the top four most consumed nuts in the world due to its health benefits and pleasant taste. Common walnut (Juglans regia L.) is one of the top four most consumed nuts in the world. Rich in unsaturated fatty acids, proteins, minerals, and vitamins, the common walnut offers many benefits to human health. It is widely grown commercially in diverse temperate regions of Asia, Europe, North and South America, South Africa, Australia, and New Zealand. As the sister taxon of J. regia, J. sigillata harbors some wild nut characteristics, which may represent a primitive form, and is mainly distributed in southwest China [2]. Knowledge of the population structure, genetic diversity, and the evolutionary history of the Chinese walnut remains limited [6]
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