Stabilising autopolyploid meiosis for enhanced yield

Introduction

Hybrid breeding has been one of the biggest contributors to yield increase of the last century. Hybrids are individuals which have genetically different parents, resulting in a “hybrid vigour” effect. This hybrid vigour effect can confer advantages over inbred parent lines in growth, yield, and resilience and tolerance to different types of environmental stresses, which is important for securing agricultural production in a changing climate.

Autopolyploids vs. Diploids

An even greater hybrid vigour effect is possible in autopolyploids, which can have up to four different copies of each chromosome, compared to diploids, which can have only up to two different copies of each chromosome. In effect, “double hybrids” can be made in autopolyploids, with up to four different parents contributing to hybrid vigour in a single individual.

Challenges in Breeding

However, to date, the double hybrid effect has almost never been used for breeding. Most of our crops are not autopolyploids. We can induce autopolyploidy through chromosome doubling, but this causes meiotic instability, where multiple crossovers occur between the four chromosome copies during meiosis.

Meiotic Instability

This pairing disruption leads to potential loss of chromosomes and chromosome fragments essential for seed fertility and viability. Although induced autopolyploids are meiotically unstable, this is not the case for established autopolyploids.

Established Autopolyploids

In the majority of established autopolyploids, a maximum of one crossover per two homologous chromosomes during meiosis is strictly enforced. This achieves 100% pairing and correct segregation of chromosomes into daughter cells.

Proposed Solution

I propose to stabilise meiosis in induced autopolyploid Brassica rapa (turnip, Chinese cabbage) by:

1. Knock-out of crossover promoting genes
2. Over-expression of crossover suppressing genes
3. Selection of natural genetic variants

Stable autopolyploids will be used to produce double-hybrid lines, which will be evaluated for hybrid vigour for yield-related traits.