15-IWYP: Molecular Dissection of Spike Yield Components in Wheat

We face a major challenge in understanding the genetic architecture of yield potential in wheat. We propose a systematic genetic approach to identify potential developmental bottlenecks in the early stages of spike and grain development. We hypothesise that this approach will contribute to the identification of novel allelic variation that will deliver step-changes in wheat yield potential. Increasing wheat yields will require simultaneous improvements of both the 'source' and 'sink' and that the various yield components must be studied together to address the known negative correlations that exist between some of these traits (e.g. grain number and weight). However, a reductionist and systematic approach can be used as an initial step to understand the gene networks regulating each individual yield component. This knowledge can then be applied to assemble the best allelic combinations.

This proposal is focused on the 'sink' side of the equation and specifically on the simultaneous increase of the number of grains per spike and the size of the individual grains. These yield components are mainly determined during a relatively narrow and well-defined window in the early stages of spike and carpel/grain development. We propose to focus on the critical early periods of spike and carpel/grain development, combine favourable alleles previously identified by our groups, and exploit exome sequenced tetraploid and hexaploid TILLING (Targeting Induced Local Lesions in Genomes) populations to identify novel allelic variants. The past wheat TILLING population will allow rapid evaluation of genes in null double-mutants, whereas the bread wheat population will complement this approach and allow deployment into elite bread wheat varieties.

In this project we will identify and characterise a set of genes regulating grain number and weight, and develop novel allelic combinations to enhance overall spike yield in wheat. We have validated a set of both natural and novel induced allelic variants from the TILLING populations that affect specific spike yield components and have systematically developed the germplasm, techniques, and functional genomics resources required to address the proposed objectives. We will exploit emerging genomic advances and will work closely with breeders to rapidly introduce this variation into CIMMYT germplasm. The variation and allelic combinations generated within this project have not previously been utilised in traditional wheat breeding programmes and, therefore, represent an unprecedented opportunity to make significant progress in the genetic yield potential of wheat.

The main direct outcomes expected from this research are:

(1) Identification and characterisation (molecular, physiological and agronomic) of novel gene variants controlling wheat spike yield components
(2) Creation of double and triple mutants targeting all homoeologs for the selected genes to overcome functional redundancy
(3) Generation of adapted germplasm with new allelic combinations affecting complementary spike yield components

Urgent action is needed to sustainably increase global wheat production. However, limited knowledge of the genes controlling wheat yield is hampering efforts to advance towards this goal using science-based solutions. The aim of this proposal is to define, characterize, and manipulate genes that regulate the early stages of spike and carpel/grain development and that govern spike yield components (grains per spike and grain weight). We will apply innovative sequencing-based approaches to exploit novel sources of induced genetic variation in these two traits to increase the genetic yield potential of wheat. We will test if this potential is realized in elite wheat varieties. Understanding the genes controlling different yield components will allow us to combine and exploit variation across all three homoeologous genomes, and to overcome the perennial problem of functional redundancy observed in polyploid wheat. The combination of novel allelic variants in genes affecting grain number and weight represents an opportunity to generate significant increases in wheat yield potential not previously exploited in wheat improvement programmes.

Who might benefit from this research?

This research will benefit a series of non-academic parties. This include wheat and cereal breeders in the UK and globally; farmers in Europe, the US and elsewhere based on our collaborative work with the International Centre for Wheat and Maize Improvement (CIMMYT); and the general public.


How might they benefit from this research?
Breeders will be those which will benefit most directly. The work and resources developed in this project will allow them to develop wheat lines with enhanced yield potential using genetic markers to track what has until now been an extremely complicated trait to follow with markers. We will generate genetic material which will be in adapted backgrounds allowing them to assess the lines in their target environments and make the most informed decisions. This project will deliver the tools for breeders to develop the next generation of wheat varieties with improved yield based on specific allelic combinations.

Farmers will benefit from having access to higher yielding wheat varieties across different target environments. They will exploit these benefits by growing wheat varieties developed after the end of the project. The fact that we will characterise the effect of different genes across development will allow us to provide combinations of genes which will enhance yield in different ways. This will allow us to develop wheat varieties which achieve enhanced yield in different ways, which we hypothesise would also be more stable yield. If this is the case, farmers would benefit enormously from having more resilient yielding wheat varieties in their fields.

The general public will benefit through access to wheat based products derived from the varieties that include the new allelic combinations and genes produced in this project. This will require time between discovery and delivery, but ultimately the general public will receive the benefits of these new varieties. The public will also benefit from having increased yielding varieties across the world since this will help maintain food security and also political stability in many countries which depend on wheat as a staple crop. Food riots and political instability in recent years have been linked to food and bread prices (for example the Arab Spring) and recent immigration to Europe is predominantly from countries that have wheat-based diets. The reasons behind immigration are complex, but improving food security in the countries of origin will be an important factor to ensure that local food demands are met and to reduce social instability.