TEOSINTE BRANCHED1 Regulates Inflorescence Architecture and Development in Bread Wheat (Triticum aestivum)

Abstract

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.

Domestication and crop evolution of wheat and barley: Genes, genomics, and future directions

“…Wheat genotypes with higher than normal levels of TB1‐D1 expression have paired spikelets at each floret rather than a single spikelet due to extra branching. The extra branching is a result of delayed development of meristem identity tissue (Dixon et al ). Homoeologs of TB1 variants affecting spike architecture also exist in the A ( TB‐A1 ) and B ( TB‐B1 ) genomes, but variants of TB‐B1 seem to have a larger impact on spike architecture than TB‐A1 (Dixon et al ).…”

Genetic pathways controlling inflorescence architecture and development in wheat and barley

“…Moreover, FT‐B1 ( FT1 from the B genome of bread wheat) acts downstream of Ppd‐1 to influence spikelet number, with loss of FT‐B1 resulting in increased spikelet number, in a thermally‐responsive manner (Dixon et al ; Finnegan et al ) (Figure ). FT1‐dependent control of spikelet architecture was also supported by recent analysis of TEOSINTE BRANCHED1 ( TB1 ; orthologue of Vrs5 ) function in wheat, which facilitates paired spikelet development, in a dosage dependent manner, by interacting with FT1 and reducing FT1‐dependent activation of spikelet meristem identity genes (Dixon et al ) (Figure ). Investigation of plants that were tetrasomic for chromosome 4D and transgenic lines that expressed TB1 at higher levels showed that increased dosage of TB1 promotes paired spikelet development, and allelic variation for TB1 was shown to be associated significantly with paired spikelets in modern wheat cultivars (Dixon et al ).…”

“…FT1‐dependent control of spikelet architecture was also supported by recent analysis of TEOSINTE BRANCHED1 ( TB1 ; orthologue of Vrs5 ) function in wheat, which facilitates paired spikelet development, in a dosage dependent manner, by interacting with FT1 and reducing FT1‐dependent activation of spikelet meristem identity genes (Dixon et al ) (Figure ). Investigation of plants that were tetrasomic for chromosome 4D and transgenic lines that expressed TB1 at higher levels showed that increased dosage of TB1 promotes paired spikelet development, and allelic variation for TB1 was shown to be associated significantly with paired spikelets in modern wheat cultivars (Dixon et al ). Taken together, these results show that transcriptional and post‐translational regulation of flowering signals can alter inflorescence architecture, which has potential to be used as a mechanism for increasing spikelet and floret numbers in wheat.…”

“…Although the function of these two Vrs5/Int‐c alleles remains unclear, comparative analysis of the predicted amino acid sequences for these two alleles ( Int‐c.a and int‐c.b ) with TB1 homologues in wheat, maize, rice, and Brachypodium distachyon shows that the Int‐c.a allele is less evolutionarily conserved than the int‐c.b allele, suggesting that six‐rowed barley contains a deleterious Vrs5/Int‐c allele with reduced function (Doebley et al , ; Takeda et al ; Ramsay et al ; Dixon et al ). This conclusion is supported by the increased lateral spikelet fertility observed in lines that contain mutations preventing production of a functional VRS5/INT‐C protein (Ramsay et al ).…”

“…The genetic relatedness of wheat and barley, in combination with the altered inflorescence and spikelet meristem determinacy of these two species, provides a unique opportunity to determine the genes and biological processes that contribute to the diverse inflorescence architecture of cereals. For example, in barley, reduced function of Vrs5 / TB1 facilitates development of the lateral spikelets, whereas in wheat, increased dosage of TB1 promotes formation of secondary spikelets, which could be interpreted to mean that Vrs5 / TB1 suppresses axillary spikelet development in barley but promotes more elaborate branching in wheat (Ramsay et al ; Dixon et al ). An alternate explanation is that Vrs5 / TB1 promotes meristem dormancy, which influences the transition of meristem determinacy and outgrowth of lateral organs.…”