Post-polyploidisation morphotype diversification associates with gene copy number variation

Sarah Schiessl,Rod Snowdon,Diana Kuehn,Bruno Huettel,Richard Reinhardt

doi:10.1038/srep41845

Abstract

Genetic models for polyploid crop adaptation provide important information relevant for future breeding prospects. A well-suited model is Brassica napus, a recent allopolyploid closely related to Arabidopsis thaliana. Flowering time is a major adaptation trait determining life cycle synchronization with the environment. Here we unravel natural genetic variation in B. napus flowering time regulators and investigate associations with evolutionary diversification into different life cycle morphotypes. Deep sequencing of 35 flowering regulators was performed in 280 diverse B. napus genotypes. High sequencing depth enabled high-quality calling of single-nucleotide polymorphisms (SNPs), insertion-deletions (InDels) and copy number variants (CNVs). By combining these data with genotyping data from the Brassica 60 K Illumina® Infinium SNP array, we performed a genome-wide marker distribution analysis across the 4 ecogeographical morphotypes. Twelve haplotypes, including Bna.FLC.A10, Bna.VIN3.A02 and the Bna.FT promoter on C02_random, were diagnostic for the diversification of winter and spring types. The subspecies split between oilseed/kale (B. napus ssp. napus) and swedes/rutabagas (B. napus ssp. napobrassica) was defined by 13 haplotypes, including genomic rearrangements encompassing copies of Bna.FLC, Bna.PHYA and Bna.GA3ox1. De novo variation in copies of important flowering-time genes in B. napus arose during allopolyploidisation, enabling sub-functionalisation that allowed different morphotypes to appropriately fine-tune their lifecycle.

Highlights

Genetic models for polyploid crop adaptation provide important information relevant for future breeding prospects
The subspecies split between oilseed/kale (B. napus ssp. napus) and swedes/rutabagas (B. napus ssp. napobrassica) was defined by 13 haplotypes, including genomic rearrangements encompassing copies of Bna.FLOWERING LOCUS C (FLC), Bna.PHYTOCHOME A (PHYA) and Bna.GA3ox[1]
By comparing results of vernalisation experiments with data from genome-wide marker distribution analysis, targeted deep-sequencing of essential flowering time regulators and the FLOWERING LOCUS T (FT) promoter, and coverage analysis to estimate copy number variants (CNVs), we provide novel insights that reveal the complexity of post-polyploidisation morphological diversification in an important crop species

Summary

Introduction

Genetic models for polyploid crop adaptation provide important information relevant for future breeding prospects. We unravel natural genetic variation in B. napus flowering time regulators and investigate associations with evolutionary diversification into different life cycle morphotypes. De novo variation in copies of important flowering-time genes in B. napus arose during allopolyploidisation, enabling sub-functionalisation that allowed different morphotypes to appropriately fine-tune their lifecycle. The morphotype with highest seed yields is the biannual winter oilseed type[8] The prerequisites for this lifecycle are winter hardiness for winter survival, along with vernalisation requirement to avoid pre-winter flowering[7]. Boreal or semi-arid regions have periods of low plant survival rates, either due to strong winter freezing or extreme heat stress. In these regions, annual spring types are prominent. The different cultivated forms are bred in separate breeding pools, with introgression between morphotypes only in cases of extreme introgression benefit

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