Regulation of wheat inflorescence architecture by a cation amino acid transporter

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An inflorescence is a group of grain-producing flowers that form on a complex arrangement of branches. Domestication and modern breeding have harnessed diversity of branch numbers and arrangements that form on an inflorescence to increase grain production, which has frequently involved modifying the activity of genes that control inflorescence development. This approach has been under-utilised in wheat as very few genes are known to regulate inflorescence architecture in this crop - we aim to identify genes that control wheat inflorescence development to help optimise yield related traits that will contribute to the 60-70% increase in global grain production required by 2050. The research proposed here will build on our group's breakthrough discovery that a mutation in a gene encoding CATION AMINO ACID TRANSPORTER1 (CAT1) dramatically effects inflorescence development in wheat, and the arrangement of branches, or spikelets, that form on the inflorescence. By deciphering the role of CAT1 during inflorescence development, the project will uncover a previously unknown role for amino acid transporters in plant reproductive biology, and will advance our understanding of molecular processes that regulate yield-related traits in cereals. We identified CAT1 as a protein that influences inflorescence architecture by performing a genetic screen to identify mutants that form an alternate arrangement of spikelets, known as 'paired spikelets'. One mutant contained mutation in the copy of CAT1 on the D genome (CAT-D1), which promotes paired spikelet development with a dominant inheritance pattern. Plants with one copy of the mutated allele (heterozygous) and two mutated copies (homozygous) form paired spikelets, and homozygous mutants display additional developmental phenotypes including severe leaf curling, additional vascular bundles (transport system within plants) and perturbed lateral root development. There is a copy of CAT1 on the B genome (CAT-B1), but not the A genome. We will investigate the amino acid transporter activity of CAT-D1 and CAT-B1 to test their functional conservation as proteins that localise to the cell membrane and transport cationic amino acids, and to assess their ability to transport the growth hormone, auxin (Objective 1). The effect of the missense mutation on CAT-D1 function will be investigated by assessing the ability of the mutant protein to transport amino acids and/or auxin, relative to the wild-type protein, using diverse experimental assays (Objective 2). We will investigate genes and molecular processes that act downstream of CAT-D1 to regulate inflorescence development by studying the involvement of auxin response pathways, which is supported by outcomes of our preliminary RNA-seq data (Objective 3). Finally, we will investigate the genetic and environmental regulation of CATD1- dependent control of inflorescence architecture by analysing the interaction between CAT1 with Photoperiod-1 and FLOWERING LOCUS T1, which are major flowering-time genes that regulate spikelet development (Objective 4). Knowledge and resources (e.g. germplasm, molecular markers) developed during the project will benefit researchers investigating molecular processes that control reproductive and developmental biology of plants, and those studying amino acid transporters in other organisms. The outputs will benefit publicly-funded and commercial breeding programmes by improving our understanding of genes that regulate inflorescence development in wheat, which will also benefit barley, rice and maize breeders. The outcomes will ultimately benefit growers and consumers by contributing to improved food security for the world's growing population, which will enhance society's quality of life and boost the UK economy.