Six-rowed spike4 ( Vrs4 ) controls spikelet determinacy and row-type in barley

Abstract

Inflorescence architecture of barley (Hordeum vulgare L.) is common among the Triticeae species, which bear one to three singleflowered spikelets at each rachis internode. Triple spikelet meristem is one of the unique features of barley spikes, in which three spikelets (one central and two lateral spikelets) are produced at each rachis internode. Fertility of the lateral spikelets at triple spikelet meristem gives row-type identity to barley spikes. Sixrowed spikes show fertile lateral spikelets and produce increased grain yield per spike, compared with two-rowed spikes with sterile lateral spikelets. Thus, far, two loci governing the row-type phenotype were isolated in barley that include Six-rowed spike1 (Vrs1) and Intermedium-C. In the present study, we isolated Sixrowed spike4 (Vrs4), a barley ortholog of the maize (Zea mays L.) inflorescence architecture gene RAMOSA2 (RA2). Eighteen coding mutations in barley RA2 (HvRA2) were specifically associated with lateral spikelet fertility and loss of spikelet determinacy. Expression analyses through mRNA in situ hybridization and microarray showed that Vrs4 (HvRA2) controls the row-type pathway through Vrs1 (HvHox1), a negative regulator of lateral spikelet fertility in barley. Moreover, Vrs4 may also regulate transcripts of barley SISTER OF RAMOSA3 (HvSRA), a putative trehalose-6-phosphate phosphatase involved in trehalose-6-phosphate homeostasis implicated to control spikelet determinacy. Our expression data illustrated that, although RA2 is conserved among different grass species, its down-stream target genes appear to be modified in barley and possibly other species of tribe Triticeae.cytokinin | EGG APPARATUS1 | grain number | yield potential

Six-Rowed Spike3 (VRS3) Is a Histone Demethylase That Controls Lateral Spikelet Development in Barley

“…1; Supplemental Fig. S1), corroborating previous reports Koppolu et al, 2013;Liller et al, 2015). The development of additional lateral spikelets, which mainly occurred at the middle part of the spike, was not associated with a significant change in rachis internode number (Supplemental Fig.…”

“…At this stage, the first floral organ primordia differentiate and the stem elongation is initiated. Moreover, initial differences between six-rowed vrs mutants and wild type are clearly visible (Koppolu et al, 2013). RNA sequencing was carried out in the ILs, the backcross recipient cv Bowman and cv Bonus, the parental line of int-a.1.…”

“…The mutations in vrs3(int-a.1) and int-c.5 are both characterized by a small deletion causing a frame shift in a histone demethylase and an ortholog of teosinte branched1 (TB1), respectively. The vrs4.k mutant carries a small deletion causing a nonsense mutation in Ra2; and the vrs1 mutant contains a nonsynonymous SNP in a homeobox (HOX) transcription factor (Komatsuda et al, 2007;Ramsay et al, 2011;Koppolu et al, 2013). We identified transcripts of 30,174 genes at W3.5 and W5.0 (Supplemental Table S3).…”

“…In addition, many of these mutant phenotypes were intercrossed to identify allelic mutant series for different morphological, developmental, and physiological traits. The collection has proven particularly valuable for studying the genetic control of plant and spike architecture Koppolu et al, 2013;Liller et al, 2015).…”

“…VRS1 encodes a HD-ZIP transcription factor (Hv.Hox1; Komatsuda et al, 2007). VRS4 encodes a LATERAL ORGAN BOUNDARY transcription factor that is homologs to the maize (Zea mays) RAMOSA2 (RA2) and acts upstream of VRS1 (Koppolu et al, 2013). In addition, a number of row-type mutants display an intermedium spike (int) phenotype with varying two-or six-rowed patterns.…”