<i>CATION AMINO ACID TRANSPORTER1</i> encodes an arginine transporter whose expression is influenced by daylength and <i>Photoperiod-1</i>

Flowering and inflorescence development of wheat involve coordination of organ development, tissue growth, and remobilisation of nutrients from source to sink tissue. Photoperiod-1 (Ppd-1) is a major flowering gene that regulates diverse genetic pathways during inflorescence development, including those that determine spikelet and floret formation; however, it is not yet known if Ppd-1 influences the expression of genes encoding proteins that transport nutrients. Here, we used transcriptome data from near-isogenic lines that contain variant Ppd-1 alleles to show that Ppd-1 is required for expression of a cation amino acid transporter, CATION AMINO ACID TRANSPORTER1 (CAT1), in developing inflorescences and leaves. The influence of Ppd-1 on CAT1 expression is supported by CAT1 activity being photoperiod responsive, with CAT1 transcripts absent in short days and accumulating as daylengths extend. Functional analysis using Xenopus oocytes supports a role for CAT1 as a transporter of cationic amino acids, including arginine, and characterisation of mutant lines lacking functional CAT-D1 and CAT-B1 show CAT1 influences amino acid levels, root growth and spikelet development. Our results indicate Ppd-1 has a broader role during wheat reproductive development by affecting the expression of amino acid transporters such as CAT1, which encodes an arginine transporter that influences development and growth of source and sink tissues.