Kreitzer, C. | Search bioRxiv

bioRxiv2020

Allelic differences of clustered terpene synthases contribute to correlated intra-specific variation of floral and herbivory induced volatiles in a wild tobacco

O_LIPlant volatile emissions can recruit predators of herbivores for indirect defence and attract pollinators to aid in pollination. Although volatiles involved in defence and pollinator attraction are primarily emitted from leaves and flowers, respectively, they will co-evolve if their underlying genetic basis is intrinsically linked, either due to pleiotropy or genetic linkage. However, direct evidence of co-evolving defence and floral traits is scarce. C_LIO_LIWe characterized intra-specific variation of herbivory-induced plant volatiles (HIPVs), the key components of indirect defence against herbivores, and floral volatiles in the wild tobacco Nicotiana attenuata. C_LIO_LIWe found that variation of (E)-{beta}-ocimene and (E)--bergamotene contributed to the correlated changes in HIPVs and floral volatiles among N. attenuata natural accessions. Intra-specific variations of (E)-{beta}-ocimene and (E)--bergamotene emissions resulted from allelic variation of two genetically co-localized terpene synthase genes, NaTPS25 and NaTPS38 respectively. C_LIO_LIAnalyzing haplotypes of NaTPS25 and NaTPS38 revealed that allelic variations of NaTPS25 and NaTPS38 resulted in correlated changes of (E)-{beta}-ocimene and (E)--bergamotene emission in HIPVs and floral volatiles in N. attenuata. C_LIO_LITogether, these results provide evidence that pleiotropy and genetic linkage result in correlated changes in defences and floral signals in natural populations, and the evolution of plant volatiles is likely under diffuse selection. C_LI

evolutionary biology↗

bioRxiv2017

Wild tobacco genomes reveal the evolution of nicotine biosynthesis

Nicotine, the signature alkaloid of Nicotiana species responsible for the addictive properties of human tobacco smoking, functions as a defensive neurotoxin against attacking herbivores. However, the evolution of the genetic features that contributed to the assembly of the nicotine biosynthetic pathway remains unknown. We sequenced and assembled genomes of two wild tobaccos, Nicotiana attenuata (2.5 Gb) and N. obtusifolia (1.5 Gb), two ecological models for investigating adaptive traits in nature. We show that after the Solanaceae whole genome triplication event, a repertoire of rapidly expanding transposable elements (TEs) bloated these Nicotiana genomes, promoted expression divergences among duplicated genes and contributed to the evolution of herbivory-induced signaling and defenses, including nicotine biosynthesis. The biosynthetic machinery that allows for nicotine synthesis in the roots evolved from the stepwise duplications of two ancient primary metabolic pathways: the polyamine and nicotinic acid dinucleotide (NAD) pathways. While the duplication of the former is shared among several Solanaceous genera which produce polyamine-derived tropane alkaloids, the innovation and efficient production of nicotine in the genus Nicotiana required lineage-specific duplications within the NAD pathway and the evolution of root-specific expression of the duplicated Solanaceae-specific ethylene response factor (ERF) that activates the expression of all nicotine biosynthetic genes. Furthermore, TE insertions that incorporated transcription factor binding motifs also likely contributed to the coordinated metabolic flux of the nicotine biosynthetic pathway. Together, these results provide evidence that TEs and gene duplications facilitated the emergence of a key metabolic innovation relevant to plant fitness.

genomics↗