Gene Locus Mapping and Candidate Gene Screening for Branched Spike and Its Associated Traits of the Ynbs Mutant in Barley

The Ynbs (Yunnan branched-spike) mutant of naked barley with a branched spike displays some special traits, such as more degenerated multiple spikelets per spike and florets per multiple spikelets and a lower seed-setting rate. However, there is still a lack of understanding the loci of the trait. In the present study, the Ynbs mutant was crossed with Baodamai8 to breed F 2 and F 2:5 populations. The F 2 and F 2:5 populations were successively employed to map the loci for a branched spike, triplicate (or multiple) spikelet number per spike (T(M)SNS), degenerated triplicate (or multiple) spikelet number per spike (DT(M)SNS) and floret number per triplicate (or multiple) spikelet (FNT(M)S). The genetic interval mapped through the F 2:5 population was flanked by markers HvSSR4 and HVSSR20, and, within that, mapped through the F 2 population. The genetic distance of the branched-spike locus to HVSSR20 locus, T(M)SNS, FNT(M)S), and DT(M)SNS is 1.86 centiMorgan (cM), 0.27 cM, and 0.73 cM, respectively. The Morex genome sequence defined by markers HvSSR4 and HVSSR20 harbored 18 genes, among which HORVU.MOREX.r3.2HG0114260 belonged to the AP2/ERF domain transcription factor gene superfamily. In the Ynbs mutant, the C base at site 232 of the code domain sequence of the gene was substituted with T, leading to the substitution of arginine with cysteine at site 78 in the DNA-binding domain of the encoded protein. The gene harbors a new allele mutant in the Ynbs mutant and exhibits a pleiotropy in the development of a branched spike, spikelet, and floret. The results provide valuable information for elucidating the development mechanism of barley young spike.