The domestication of cereal crops such as wheat, maize, rice and barley has included the modification of inflorescence architecture to improve grain yield and ease harvesting(1). Yield increases have often been achieved through modifying the number and arrangement of spikelets, which are specialized reproductive branches that form part of the inflorescence. Multiple genes that control spikelet development have been identified in maize, rice and barley(2-5). However, little is known about the genetic underpinnings of this process in wheat. Here, we describe a modified spikelet arrangement in wheat, termed paired spikelets. Combining comprehensive QTL and mutant analyses, we show that Photoperiod-1 (Ppd-1), a pseudo-response regulator gene that controls photoperiod-dependent floral induction, has a major inhibitory effect on paired spikelet formation by regulating the expression of FLOWERING LOCUS T (FT)(6,7). These findings show that modulated expression of the two important flowering genes, Ppd-1 and FT, can be used to form a wheat inflorescence with a more elaborate arrangement and increased number of grain producing spikelets.

The flowers of major cereals are arranged on reproductive branches known as spikelets, which group together to form an inflorescence. Diversity for inflorescence architecture has been exploited during domestication to increase crop yields, and genetic variation for this trait has potential to further boost grain production. Multiple genes that regulate inflorescence architecture have been identified by studying alleles that modify gene activity or dosage; however, little is known in wheat. Here, we show () regulates inflorescence architecture in bread wheat () by investigating lines that display a form of inflorescence branching known as "paired spikelets." We show that TB1 interacts with FLOWERING LOCUS T1 and that increased dosage of alters inflorescence architecture and growth rate in a process that includes reduced expression of meristem identity genes, with allelic diversity for found to associate genetically with paired spikelet development in modern cultivars. We propose coordinates formation of axillary spikelets during the vegetative to floral transition and that alleles known to modify dosage or function of could help increase wheat yields.

The advantages of free threshing in wheat led to the selection of the domesticated allele, which is now present in almost all modern wheat varieties. and the pre-domestication allele, , encode an AP2 transcription factor, with the domesticated allele conferring a free-threshing character and a subcompact (i.e. partially compact) inflorescence (spike). We demonstrate that mutations in the miR172 binding site of the gene are sufficient to increase transcript levels via a reduction in miRNA-dependent degradation, consistent with the conclusion that a single nucleotide polymorphism in the miRNA binding site of relative to was essential in defining the modern allele. We describe novel gain- and loss-of-function alleles of and use these to define new roles for this gene in spike development. is required for the suppression of 'sham ramification', and increased Q expression can lead to the formation of ectopic florets and spikelets (specialized inflorescence branches that bear florets and grains), resulting in a deviation from the canonical spike and spikelet structures of domesticated wheat.