BS-D275: A novel locus on the chromosome arm 2DS governing branched spike development in wheat

Abstract

BS-D275, a new locus on chromosome arm 2DS, is genetically independent of WFZP-2D and controls branched spike architecture in common wheat (Triticum aestivum). Branched spikes enhance wheat yield potential by increasing grain number. We identified the locus BS-D275 for spike branching in the winter wheat line Dong 275 and mapped it to chromosome arm 2DS using a recombinant inbred line (RIL) population derived from the cross of Dong 275 (branched spikes) × Zhongmai 175 (standard spikes). Across multiple field trials, spike branching and awn length segregated as polygenic, unlinked traits. Bulk segregant RNA-seq (BSR-Seq) of leaf and inflorescence samples, integrated with molecular markers, delimited BS-D275 to a 1.52-cM interval spanning 829 kb (84.03-84.86 Mb) in the Chinese Spring telomere-to-telomere reference genome. Diagnostic markers and sequence comparison positioned BS-D275 11 Mb distal to the spike-branching locus WFZP-2D (73.09 Mb), confirming their independence. The interval contains 10 inflorescence-specific candidate genes. CSIAAS2DG0371200/TraesCS2D02G133500, encoding a GTPase-activating protein, carries a Dong 275-specific 4-bp frameshift and is highly expressed in spikes, making it the most likely candidate for BS-D275. Parallel BSR-Seq of awned versus tip-awned bulks mapped the awn suppressor to the B1 locus (CSIAAS5AG1310200/TraesCS5A02G542800) on chromosome arm 5AL, demonstrating that awn development and spike branching are under separate genetic control. WFZP-2D represses awn development while BS-D275 does not, which provides evidence that BS-D275 is most likely a novel regulator of spike branching. Diagnostic markers for BS-D275 will accelerate marker-assisted selection for high-yielding, branched-spike wheat.