Sequence based mapping identifies a candidate transcription repressor underlying awn suppression at the B1 locus in wheat

Authors: DEWITT, NOAH - North Carolina State University; GUEDIRA, MOHAMMED - North Carolina State University; LAUER, EDWIN - North Carolina State University; SARINELLI, MARTIN - North Carolina State University; TYAGI, PRIYANKA - North Carolina State University; FU, DAOLIN - University Of Idaho; HAO, QUNQUN - University Of Idaho; MURPHY, J - North Carolina State University; Marshall, David; AKHUNOVA, ALINA - Kansas State University; JORDAN, KATHERINE - Kansas State University; AKHUNOV, EDUARD - Kansas State University; Brown-Guedira, Gina

Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2019
Publication Date: 8/19/2019
Citation: Dewitt, N., Guedira, M., Lauer, E., Sarinelli, M., Tyagi, P., Fu, D., Hao, Q., Murphy, J. P., Marshall, D.S., Akhunova, A., Jordan, K., Akhunov, E., Brown Guedira, G.L. 2019. Sequence based mapping identifies a candidate transcription repressor underlying awn suppression at the B1 locus in wheat. New Phytologist. 225:326–339. https://doi.org/10.1111/nph.16152.
DOI: https://doi.org/10.1111/nph.16152

Interpretive Summary: Awns are stiff, hair-like structures that grow from the lemmas of wheat. Awns are thought to contribute to yield in warmer, drier environments, supplying carbohydrates to developing grain. However, awnless wheat varieties are the dominant type in many areas of the world, suggesting that absence of awns may be favored in some environments. Variation in awn length in domesticated wheat is primarily controlled by three major genes, most commonly the dominant awn suppressor Tipped1 (B1). This study identifies a transcription repressor responsible for awn inhibition at the B1 locus. Association mapping was combined with analysis in bi-parental populations to delimit B1 to a distal region of 5AL co-localized with QTL for number of spikelets per spike, kernel weight, kernel length, and test weight. Fine-mapping located B1 to a region containing only two predicted genes, including C2H2 zinc finger transcriptional repressor up-regulated in developing spikes of awnless individuals. Deletions encompassing this candidate gene were present in awned mutants of an awnless wheat. Sequence polymorphisms in the B1 coding region were not observed in diverse wheat germplasm while a nearby polymorphism was highly predictive of awn suppression. Transcriptional repression by B1 is the major determinant of awn suppression in global wheat germplasm. It is associated with increased number of spikelets per spike and decreased kernel size. Improved understanding of the relationship between awn development and wheat grain yield components can accelerate the improvements required to satisfy future food demands.

Technical Abstract: Awns are stiff, hair-like structures which grow from the lemmas of wheat (Triticum aestivum L.) and other grasses that contribute to photosynthesis and play a role in seed dispersal. Variation in awn length in domesticated wheat is primarily controlled by three major genes, most commonly the dominant awn suppressor Tipped1 (B1). This study identifies a transcription repressor responsible for awn inhibition at the B1 locus. Association mapping was combined with analysis in bi-parental populations to delimit B1 to a distal region of 5AL co-localized with QTL for number of spikelets per spike, kernel weight, kernel length, and test weight. Fine-mapping located B1 to a region containing only two predicted genes, including C2H2 zinc finger transcriptional repressor TraesCS5A02G542800 up-regulated in developing spikes of awnless individuals. Deletions encompassing this candidate gene were present in awned mutants of an awnless wheat. Sequence polymorphisms in the B1 coding region were not observed in diverse wheat germplasm while a nearby polymorphism was highly predictive of awn suppression. Transcriptional repression by B1 is the major determinant of awn suppression in global wheat germplasm. It is associated with increased number of spikelets per spike and decreased kernel size.