Increased and ectopic expression of<i>Triticum polonicum VRT-A2</i>underlies elongated glumes and grains in hexaploid wheat in a dosage-dependent manner

AbstractFlower development is a major determinant of yield in crops. In wheat, natural variation for the size of spikelet and floral organs is particularly evident inTriticum polonicum, a tetraploid subspecies of wheat with long glumes, lemmas, and grains. Using map-based cloning, we identifiedVRT2, a MADS-box transcription factor belonging to theSVPfamily, as the gene underlying theT. polonicumlong-glume (P1)locus. The causalP1mutation is a sequence re-arrangement in intron-1 that results in both increased and ectopic expression of theT. polonicum VRT-A2allele. Based on allelic variation studies, we propose that the intron-1 mutation inVRT-A2is the uniqueT. polonicumspecies defining polymorphism, which was later introduced into hexaploid wheat via natural hybridizations. Near-isogenic lines differing for theP1locus revealed a gradient effect ofP1across florets. Transgenic lines of hexaploid wheat carrying theT. polonicum VRT-A2allele show that expression levels ofVRT-A2are highly correlated with spike, glume, grain, and floral organ length. These results highlight how changes in expression profiles, through variation incis-regulation, can impact on agronomic traits in a dosage-dependent manner in polyploid crops.One-sentence summaryAn intron-1 rearrangement in the MADS-box transcription factorVRT-A2leads to its misexpression and defines the long-glume phenotype of Polish wheat (T. polonicum).