Genome sequencing and population genomic analyses provide insights into the adaptive landscape of silver birch
Nat Genet. 2017, 49(6):904-912

Salojärvi J, Smolander OP, Nieminen K, Rajaraman S, Safronov O, Safdari P, Lamminmäki A, Immanen J, Lan T, Tanskanen J, Rastas P, Amiryousefi A, Jayaprakash B, Kammonen JI, Hagqvist R, Eswaran G, Ahonen VH, Serra JA, Asiegbu FO, de Dios Barajas-Lopez J, Blande D, Blokhina O, Blomster T, Broholm S, Brosché M, Cui F, Dardick C, Ehonen SE, Elomaa P, Escamez S, Fagerstedt KV, Fujii H, Gauthier A, Gollan PJ, Halimaa P, Heino PI, Himanen K, Hollender C, Kangasjärvi S, Kauppinen L, Kelleher CT, Kontunen-Soppela S, Koskinen JP, Kovalchuk A, Kärenlampi SO, Kärkönen AK, Lim KJ, Leppälä J, Macpherson L, Mikola J, Mouhu K, Mähönen AP, Niinemets Ü, Oksanen E, Overmyer K, Palva ET, Pazouki L, Pennanen V, Puhakainen T, Poczai P, Possen BJHM, Punkkinen M, Rahikainen MM, Rousi M, Ruonala R, van der Schoot C, Shapiguzov A, Sierla M, Sipilä TP, Sutela S, Teeri TH, Tervahauta AI, Vaattovaara A, Vahala J, Vetchinnikova L, Welling A, Wrzaczek M, Xu E, Paulin LG, Schulman AH, Lascoux M, Albert VA, Auvinen P, Helariutta Y, Kangasjärvi J

Abstract
Silver birch (Betula pendula) is a pioneer boreal tree that can be induced to flower within 1 year. Its rapid life cycle, small (440-Mb) genome, and advanced germplasm resources make birch an attractive model for forest biotechnology. We assembled and chromosomally anchored the nuclear genome of an inbred B. pendula individual. Gene duplicates from the paleohexaploid event were enriched for transcriptional regulation, whereas tandem duplicates were overrepresented by environmental responses. Population resequencing of 80 individuals showed effective population size crashes at major points of climatic upheaval. Selective sweeps were enriched among polyploid duplicates encoding key developmental and physiological triggering functions, suggesting that local adaptation has tuned the timing of and cross-talk between fundamental plant processes. Variation around the tightly-linked light response genes PHYC and FRS10 correlated with latitude and longitude and temperature, and with precipitation for PHYC. Similar associations characterized the growth-promoting cytokinin response regulator ARR1, and the wood development genes KAK and MED5A.

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