A natural variation of an SVP MADS-box transcription factor in Triticum petropavlovskyi leads to its ectopic expression and contributes to elongated glume

Abstract

Triticum petropavlovskyi, commonly known as Xinjiang rice wheat, is a unique hexaploidy wheat grown in the Xinjiang area. T. petropavlovskyi is marked by its elongated glume (Eg) trait, which is controlled by gene P1 pet located on chromosome 7A (Wang et al., 2002;Watanabe and Imamura, 2002). The origin of T. petropavlovskyi has been disputed. It is generally accepted that P1 pet was introduced from tetraploid polish wheat (T. polonicum) via a hybridization with hexaploid common wheat (T. aestivum) (Akond et al., 2008;Chen et al., 2016). The P1 pet has pleiotropic effects in the increase of spike length, grain length, and grain weight, and decrease of fertility, grain number, and awn length (Okamoto et al., 2013), indicating the potential impact of P1 pet on grain yield-related traits. The cloning of P1 pet will provide evidence for the prognosis of whether a mutation at P1 in T. petropavlovskyi or T. polonicum gave rise to the Eg trait and facilitate the utilization of this unique species in breeding for yield improvement.

The T. ispahanicum elongated glume locus P2 maps to chromosome 6A and is associated with the ectopic expression of SVP-A1

“…Recently, multiple groups identified VRT-A2 as the causal gene for P1 (Adamski et al 2021;Liu et al 2021;Xiao et al 2021). We therefore compared the sequence of VRT-B2 (TraesCS7B02G080300) in five T. ispahanicum accessions to Chinese Spring (RefSeqv1.0).…”

“…We identified three clades consistent with a monocot-specific triplication of StMADS11-like genes. Proteins from each clade have been shown to influence glume or lemma length when ectopically expressed in wheat (Adamski et al 2021;Liu et al 2021;Xiao et al 2021), maize (Han et al 2012;Wingen et al 2012), rice (Sentoku et al 2005), and barley (Trevaskis et al 2007). The biological function of previously characterized SVP/StMADS11-like protein in grasses, alongside the fine-mapping data, makes SVP-A1 a promising candidate gene for P2.…”

“…The gene underlying the long-glume phenotype of T. polonicum and T. petropavlovsky was previously mapped to the P1 locus on chromosome 7A (Watanabe et al 1996). Recently, several groups have independently discovered that the long-glume and lemma phenotypes of P1 are caused by the ectopic expression of VEGETATIVE TO REPRODUCTIVE TRANSITION 2 (VRT2), a MADS-box transcription factor belonging to the SHORT VEGETATIVE PHASE (SVP)/StMADS11-like subfamily (Adamski et al 2021;Liu et al 2021;Schilling et al 2020;Xiao et al 2021). Interestingly, genes from this subfamily also influence glume and lemma length across different grass species.…”

Shaping polyploid wheat for success: Origins, domestication, and the genetic improvement of agronomic traits

“…A recent study suggested that the deletion/insertion variation in VRT-A2 intron 1 might also cause intron retention and, therefore, a frame-shift mutation (Chai et al, 2021). More interestingly, a sequence rearrangement identical to that of VRT-A2 has been detected in T. petropavlovskyi (also known as "Daosuimai" or rice-head wheat), a hexaploid wheat subspecies that also has elongated glumes (Liu et al, 2021;Xiao et al, 2021). Together, these studies support two major conclusions: (i) the activation of VRT-A2 facilitated the origin of T. polonicum as a unique species; and (ii) the long-glume trait of T. polonicum was likely inherited by T. petropavlovskyi through a genomic hybridization between T. polonicum and an unknown hexaploid landrace, enabling the formation of T. petropavlovskyi as a special subspecies of T. aestivum (Dixon and Boden, 2021;Xiao et al, 2021;Xu et al, 2021).…”

“…Notably, some species‐forming genes, for example VRT‐A2 and Tasg‐D1 , also affect the development of grains, illustrating their pleiotropic effects. Ectopic expression of VRT‐A2 in Polish wheat promotes grain elongation without affecting grain width, resulting in increased grain size and weight (Backhaus et al, 2021; Liu et al, 2021; Xiao et al, 2021). In contrast, gain‐of‐function of Tasg‐D1 in Indian dwarf wheat leads to small, round grains by repressing BR signaling, suggesting that Tasg‐D1 , in contrast to VRT‐A2 , restricts grain development (Cheng et al, 2020).…”