Abstract
BackgroundNicotiana rustica (Aztec tobacco), like common tobacco (Nicotiana tabacum), is an allotetraploid formed through a recent hybridization event; however, it originated from completely different progenitor species. Here, we report the comparative genome analysis of wild type N. rustica (5 Gb; 2n = 4x = 48) with its three putative diploid progenitors (2.3–3 Gb; 2n = 2x =24), Nicotiana undulata, Nicotiana paniculata and Nicotiana knightiana.ResultsIn total, 41% of N. rustica genome originated from the paternal donor (N. undulata), while 59% originated from the maternal donor (N. paniculata/N. knightiana). Chloroplast genome and gene analyses indicated that N. knightiana is more closely related to N. rustica than N. paniculata. Gene clustering revealed 14,623 ortholog groups common to other Nicotiana species and 207 unique to N. rustica. Genome sequence analysis indicated that N. knightiana is more closely related to N. rustica than N. paniculata, and that the higher nicotine content of N. rustica leaves is the result of the progenitor genomes combination and of a more active transport of nicotine to the shoot.ConclusionsThe availability of four new Nicotiana genome sequences provide insights into how speciation impacts plant metabolism, and in particular alkaloid transport and accumulation, and will contribute to better understanding the evolution of Nicotiana species.
Highlights
Nicotiana rustica (Aztec tobacco), like common tobacco (Nicotiana tabacum), is an allotetraploid formed through a recent hybridization event; it originated from completely different progenitor species
Assembly and annotation We sequenced the genomes of N. rustica and its potential progenitors, N. undulata, N. paniculata and N. knightiana, using reads from Illumina HiSeq2500 and Pacific Biosciences RSII sequencers and performed de novo genome assemblies
The estimations of their genome sizes based on 31-k-mer depth distributions of raw sequencing reads were 4.99 Gb for N. rustica, 2.18 Gb for N. undulata, 3.26 Gb for N. paniculata and 3.12 Gb for N. knightiana, which are consistent with the sizes (5.181, 2.362, 2.880 and 3.090 Gb, respectively) reported in the KEW c-DNA database
Summary
Nicotiana rustica (Aztec tobacco), like common tobacco (Nicotiana tabacum), is an allotetraploid formed through a recent hybridization event; it originated from completely different progenitor species. Because of even higher levels of citric acid (15–20% of dry leaf weight), the leaves of N. rustica are an excellent source of this important metabolite [2]. On the opposite to the nicotine level N. rustica exhibits a lower leaf versus root cadmium ratio compared to N. tabacum [5, 6]. As root is both involved in nicotine synthesis, cadmium uptake and shoot
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