The Barley Homeobox Transcription Factor VRS1 Influences Both Leaf Width and Vein Number

A crop's canopy structure, largely determined by the size and angle of the leaves, contributes significantly to its photosynthetic efficiency and so ultimately to its economic yield. The homeobox transcription factor, Six-rowed spike 1 (Vrs1), present in major genera of tribe Triticeae, is the genetic basis of the two-rowed vs six-rowed spike in barley. Here, both a genome-wide association analysis and a comparison between the allelic status of Vrs1 consistently indicated that the same transcription factor also regulates both leaf development and canopy architecture by an effect on the size of the flag leaf and the number of leaf veins which are developed. A histological analysis of the leaves borne by plants harbouring vrs1, in combination with an analysis of its transcriptome, revealed that the transcription factor's control over vein number and leaf width is achieved by regulating cell proliferation.