Connecting the dots for flowering time genes in wheat

There is an urgent need to increase food security. The world’s population is growing, the climate is changing, and yet the annual gains in crop yields are plateauing. To meet the demands of the future, we must take new approaches to improve crop productivity. Plants integrate seasonal progression in daylength and temperature to determine the optimal time to flower and set seed. However, in wheat, we understand very little about this process. The overall aim of this thesis is to understand how the leaf and developing inflorescence of bread wheat detects and responds to the changing seasons, and to investigate crosstalk between these tissues. Using lines containing variant alleles for the key photoperiod gene, Photoperiod‐1 (Ppd‐1), I analysed the molecular processes controlling flowering in the field. I find discrete photoperiod changes cause a step-wise increase in the transcription of FLOWERING LOCUS T1 (FT1) as the major floral activator. This seasonal induction is partially regulated by Ppd-1, which dynamically responds to changes in daylength to control the rate of inflorescence development in a ‘checkpoint’ dependent manner. Photoperiod insensitive alleles of Ppd-1 override this step-wise increase in FT1 expression, resulting in accelerated inflorescence development. Within the developing inflorescence, these leaf-derived signals have a powerful influence over gene expression, with Ppd-1 allelism altering gene expression patterns, amplitude and genome biases. Ppd-1 mediated inflorescence development involves many genes, with large clusters of gene expression focused to each key developmental stage. Investigating the genes involved in these transitions has revealed four previously uncharacterised genes that help regulate inflorescence development. In addition, temperature can influence the rate of these stage transitions, likely through leaf- and inflorescence-based pathways. This research has expanded our understanding of how wheat regulates flowering, providing a strong foundation to increase yield by fine-tuning photoperiod-depended control over spikelet and floret development

Harnessing landrace diversity empowers wheat breeding

Harnessing genetic diversity in major staple crops through the development of new breeding capabilities is essential to ensure food security1. Here we examined the genetic and phenotypic diversity of the A.E. Watkins landrace collection2 of bread wheat (Triticum aestivum), a major global cereal, through whole-genome re-sequencing (827 Watkins landraces and 208 modern cultivars) and in-depth field evaluation spanning a decade. We discovered that modern cultivars are derived from just two of the seven ancestral groups of wheat and maintain very long-range haplotype integrity. The remaining five groups represent untapped genetic sources, providing access to landrace-specific alleles and haplotypes for breeding. Linkage disequilibrium (LD) based haplotypes and association genetics analyses link Watkins genomes to the thousands of high-resolution quantitative trait loci (QTL), and significant marker-trait associations identified. Using these structured germplasm, genotyping and informatics resources, we revealed many Watkins-unique beneficial haplotypes that can confer superior traits in modern wheat. Furthermore, we assessed the phenotypic effects of 44,338 Watkins-unique haplotypes, introgressed from 143 prioritised QTL in the context of modern cultivars, bridging the gap between landrace diversity and current breeding. This study establishes a framework for systematically utilising genetic diversity in crop improvement to achieve sustainable food security.</p