Understanding the genetic basis for slow plant-mediated proteolysis in festulolium hybrids (PhD)

Summary

Ruminant protein use is inefficient and leads to losses of N and harmful greenhouse gas emissions. Previous research indicated this was in part due to inefficient plant-mediated protein break-down, particularly by ryegrasses, a consequence of the stresses encountered within the rumen. A fescue species (Festuca glaucescens) was shown in preliminary work to possibly be more resilient to abiotic stress and has a potential to aid protein protection.

The overall aim of this project was to confirm the potential to combine the forage production and quality of ryegrasses with complementary traits derived from its wild type relative, the Mediterranean-based fescue species (Festuca glaucescens). A particular aim was the inclusion of specific stress tolerance traits capable of providing for improved protein stability to assist livestock nutrient-use-efficiency and as result lower their greenhouse gas emissions. There is a hypothesis that natural adaptations in the fescue that protect plant proteins from high temperature stresses due to the species’ adaptations to grow in a warm climate, may also provide protection for grass protein from heat and other stresses when in the rumen.

Having confirmed, under simulated conditions, that the fescue was indeed more tolerant to rumen-like conditions than was ryegrass, the objective was then to discover the optimal ryegrass/fescue genome dosage required to combine the forage quality attributes of ryegrass and express the protein protection mechanism present in the fescue. Alternative genome numbers of both Italian and perennial ryegrass were assessed in turn in combination with contrasting genome numbers of the fescue in order to select overall the optimal genome complement required to ensure the most positive benefits.

In addition this, the levels of within-species variation for protein protection and stability in both ryegrass and the fescue species was also assessed including any benefits accrued from increasing genome size from a diploid to tetraploid.

For the first time, the efficiency of a targeted introgression breeding approach was also assessed whereby a limited number of fescue genes were transferred into an otherwise undisturbed perennial ryegrass genome complement. A similar backcross breeding programme had previously successfully transferred genes for drought and heat tolerance from the same fescue species into ryegrass.

Amongst the combinations assessed, the amphiploid breeding approach that provided balanced F1 hybrid genome complements of fescue and ryegrass achieved the greatest protein stability. Interactions between the ryegrass and fescue genomes in the F1 provided enhanced protein retention compared to one and often both their respective ryegrass and fescue parents plants. Both individual ryegrass and fescue plants showed large within-species variation in protein stability but this per se was no indicator for protein stability found in their progeny.

Backcross breeding programmes led to unbalanced ryegrass/fescue genome combinations and negated their positive F1 hybrid interactions. The initial lower protein content of the F1 compared to their parental genotypes may have contributed to their superior protein stability. Novel proteins were induced in the F1 hybrids by rumen-simulated stress that were not evident in ryegrasses and may have contributed to enhance protein stability.

A detailed introgression breeding programme was undertaken to assess the efficacy for overall fescue gene transfers and trait expression in perennial ryegrass. Both fescue-specific traits and genetic markers were identified that were later transmitted and expressed in high numbers in backcross derived progeny. Their high transmission confirms the efficacy of an introgression-breeding approach for transfers of valuable Festuca glaucescens traits such as deep rooting into perennial ryegrass.

Sector:

Beef & Lamb

Project code:

7778

Date:

01 October 2010 - 30 September 2013

Funders:

Hybu Cig Cymru - Meat Promotion Wales (HCC), Quality Meat Scotland

AHDB sector cost:

£42,664

Total project value:

£53,660

Project leader:

Aberystwyth University

Downloads

About this project

The Challenge

Ruminant farming uses approximately half of the UK land area and has benefited from continual developments in forage species for use in improved pastures. The use of improved pasture land for ruminant production has had a major impact on productivity but inefficiencies in the rumen (associated with excessive rates of degradation of forage protein), mean that capture of resource is still poor compared with potential gains; beef cattle on high quality pasture ingesting 400g dietary protein/day can deposit up to 240g/day of urinary N, which has consequences for both nitrate leaching to ground-water and release of nitrous oxide (a potent greenhouse gas) to the atmosphere. This project will address how plant genome-based differences in endogenous mechanisms for survival during stress could be exploited and their expression optimised via changes in gene dosage in forage grass hybrids. The aim is to promote preservation of plant protein (and hence decrease degradation of herbage protein) in the rumen and to increase rumen efficiency through improved utilisation of feed protein. A solution based on altering herbage characteristics is appropriate to the industry because using supplementary feeds to balance diets is often uneconomic or impractical in a grazing situation.

The Project

To determine optimal ryegrass and fescue genome complements required to maximise gene expression for protein stabilisation and to inform breeders of the strategies for their use in plant breeding
To test the hypothesis that natural adaptations in Mediterranean grasses to protect plant proteins against high temperatures can also protect protein in the rumen and so improve animal nutrition
To develop functional gene markers for Hsps for use in marker-assisted breeding to aid food security and to combat climate change
Marker-assisted-breeding to transfer fescue Hsp sequences into high sugar perennial ryegrass to combine alternative strategies for improved rumen N-use efficiency

Student

Sally O'Donovan