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Common wheat is an allohexaploid (BBAADD) that originated from the hybridization and polyploidization of the diploid Aegilops tauschii (DD) with the allotetraploid Triticum turgidum (BBAA). Phenotypic changes often arise with the formation and evolution of allopolyploid wheat, but little is known about the evolution of root traits in different wheat species with varying ploidy levels. Here, we reported that the lateral root number on the primary root (LRNPR) of synthetic and natural allohexaploid wheats (BBAADD) is significantly higher than that of their allotetraploid (BBAA) and diploid (AA and SS) progenitors, but is much lower than that of their diploid (DD) progenitors. The expression of the wheat gene TaLBD16, an ortholog of the Arabidopsis LATERAL ORGAN BOUNDARIES-DOMAIN16/ASYMMETRIC LEAVES2-LIKE18 (LBD16), which is involved in lateral root development in Arabidopsis, was positively correlated with the LRNPR in diploid and allopolyploid wheats. In natural and synthetic allohexaploid wheats, the transcript of the TaLBD16 from the D genome (TaLBD16-D) was relatively more abundant compared with TaLBD16-A and TaLBD16-B. Consistent with the observed variation in LRNPR, the divergence in the expression of TaLBD16 homoeologous genes occurred before the formation of polyploidy wheat. Collectively, our observations indicate that the D genome played a crucial role in the increased lateral root number of allohexaploid wheats compared with their allotetraploid progenitors, and that TaLBD16-D was one of the key genes involved in the formation of lateral root number during wheat evolution.

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Key message Two QTL with pleiotropic effects on plant height and spike length linked in coupling phase on chromosome 2DS were dissected, and diagnostic marker for each QTL was developed. Abstract Plant height (PHT) is a crucial trait related to plant architecture and yield potential, and dissection of its underlying genetic basis would help to improve the efficiency of designed breeding in wheat. Here, two quantitative trait loci (QTL) linked in coupling phase on the short arm of chromosome 2D with pleiotropic effects on PHT and spike length, QPht/Sl.cau - 2D.1 and QPht/Sl.cau - 2D.2, were separated and characterized. QPht/Sl.cau - 2D.1 is a novel QTL located between SNP makers BS00022234_51 and BobWhite_rep_c63957_1472. QPht/Sl.cau - 2D.2 is mapped between two SSR markers, SSR - 2062 and Xgwm484 , which are located on the same genomic interval as Rht8 . Moreover, the diagnostic marker tightly linked with each QTL was developed for the haplotype analysis using diverse panels of wheat accessions. The frequency of the height-reduced allele of QPht/Sl.cau - 2D.1 is much lower than that of QPht/Sl.cau - 2D.2 , suggesting that this novel QTL may be an attractive target for genetic improvement. Consistent with a previous study of Rht8 , a significant difference in cell length was observed between the NILs of QPht/Sl.cau - 2D.2 . By contrast, there was no difference in cell length between NILs of QPht/Sl.cau - 2D.1 , indicating that the underlying molecular mechanism for these two QTL may be different. Collectively, these data provide a new example of QTL dissection, and the developed diagnostic markers will be useful in marker-assisted pyramiding of QPht/Sl.cau - 2D.1 and/or QPht/Sl.cau - 2D.2 with the other genes in wheat breeding. Electronic supplementary material The online version of this article (10.1007/s00122-019-03318-z) contains supplementary material, which is available to authorized users.