Fertility Crisis: harnessing the genomic tension behind pollen fertility in sorghum

Project Description

Hybrid sorghum varieties yield more grain than inbred varieties but the method for producing hybrid seed relies on the production of so called female plants that do not produce pollen via the use of cytoplasmic male sterility which are crossed with male parents that produce pollen and result in the production of fertile hybrid seed. Unfortunately this system is complex and some female plants produce pollen in seed production fields resulting in unsaleable seed.

This project will identify the genes responsible for a trait that makes hybrid seed production possible and this knowledge will help raise sorghum yields in Australian and in some of the world’s poorest countries.

The broad aim of this project is to increase our understanding of the genetic control, physiological basis, and evolution of pollen fertility restoration in cytoplasmic male sterility systems in sorghum. In many species, F1 progeny resulting from crosses between genetically different parents commonly show superior performance for fitness traits than either of the two parents. This phenomenon, known as heterosis or hybrid vigour, has been exploited to increase productivity by breeders in a number of animal and crop species. In crop species, the major constraint to the exploitation of heterosis is the capacity to economically produce large quantities of F1 seed, given that most crop plants self-fertilize. CMS has been exploited by plant breeders for the economic production of hybrid seed in a number of crop species including sorghum, maize, and sunflowers, as the male-sterile plants cannot self-fertilize, and therefore all seed harvested from them should be F1 hybrid seed. In the developed world, sorghum cultivars are exclusively F1 hybrids, but in the developing world inbred varieties predominate, because of the technical complexity of hybrid breeding systems. Hybrid varieties generally yield ~ 30% more than inbred varieties and are more resilient to environmental stresses. It is likely, therefore, that the use of hybrid seed technology in the developing world could significantly contribute to increasing cereal production. Improved knowledge of the genetic control of CMS and fertility restoration will facilitate the adoption of hybrid technology in the developing world.

In the developed world, the lack of detailed understanding of the genetic control of fertility restoration and its interaction with the environment places considerable constraints on the genetic progress that can be made by sorghum breeders. This leads to increased costs, loss of efficiency, and a reduced capacity to exploit heterosis leading to a reduction in the amount of genetic gain achieved per year and per dollar invested. This project addresses an immediate and major problem facing commercial seed companies worldwide and also links directly to the larger problem of the need to increase crop yields more generally.

The project’s aims are as follows:

  1. Identify regions of the nuclear genome containing genes for fertility restoration (Rf genes) and partial fertility (Pf genes) in cultivated sorghum using genetic linkage mapping, association mapping, and bioinformatics.
  2. Catalogue all Rf-like genes and examine their allelic variability using a whole genome sequencing resource generated from 44 different sorghum ecotypes including cultivated and wild accessions, leading to the identification of putative functional allelic variants of the identified Rf and Pf genes.
  3. Generate a DNA haplotype map (HapMap) of sorghum mitochondrial genomes and identify candidate genes for cytoplasmic male sterility (CMS).
  4. Determine the impact of genetic and environmental factors on the expression of nuclear and mitochondrial genes by transcriptome sequencing of male-fertile and male-sterile genetic stocks (e.g., near-isogenic lines), cytoplasmic (alloplasmic) lines, and quantifying the effect of temperature on the expression of Rf-related transcripts.

Use the mechanistic insights we have gained about fertility restoration to develop predictive tools to enable the rapid assessment of sorghum lines of unknown fertility restoration status under a range of environmental conditions.

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