Molecular and genetic networks determining row number in cultivated barley.

野生大麦，最初的驯化形式和大多数目前的精英英国栽培品种产生两排籽粒，在花序或穗的两侧产生小穗。然而，在驯化后不久，出现了六行大麦，最终主导了早期的大麦种植。被称为六行穗1（VRS 1）的单个基因的突变已被确定为负责这一重要的发育开关。在二列型中，VRS 1 mRNA在保持不育的侧小穗的祖细胞中表达，这大概是因为VRS 1蛋白抑制了“侧育性”发育所需的基因的表达。通过突变使VRS 1失活将解除侧育基因的表达抑制，导致六列穗。虽然VRS 1是这一过程的核心，但我们也从大麦突变体的历史研究中了解到，至少有11个不同的六列穗基因影响侧小穗的育性程度。例如，我们最近鉴定了六棱穗5（VRS 5），并表明该基因的不同版本（我们称之为“等位基因”）总是与商业二棱和六棱大麦中不同版本的VRS 1配对。这种配对很重要，因为在具有六行版本的VRS 1（表示为vrs 1）的品系中，两行VRS 5等位基因（Vrs 5）导致从侧小穗发育小谷粒。相比之下，VRS 5（vrs 5）的六行版本导致侧小穗充分发育，对产量有重要影响。这一观察结果表明，获得VRS基因的等位基因的正确组合是极其重要的。虽然突变体研究已经确定了许多VRS基因，我们最近表明，只有四个基因的自然变异与确定目前的精英英国大麦品种是否是遗传最佳的两行或六行类型。正如预期的那样，其中一个是VRS 1，另一个是VRS 5。我们最近确定了第三个基因为VRS 3，并试图确定第四个，这与11个VRS突变体中的任何一个的位置都不一致。与此同时，德国合作者已经确定了VRS 4。虽然我们现在知道这些基因通过参与恢复生育力的发育途径内在地联系在一起，但目前我们不知道这些成分是否或如何相互作用，还涉及哪些其他基因/蛋白质，或者自物种驯化以来的10，000年中，六排类型是如何进化的。这些都是我们计划在这个项目中解决的问题。我们相信，更好地了解这一基本的发育过程将为我们如何利用控制植物形态和结构的基因变异最终提高植物产量提供见解。

Wild barleys, the original domesticated forms and the majority of current elite UK cultivars produce two rows of grain bearing spikelets either side of the inflorescence, or spike. However, soon after the domestication, barleys with six rows of grain emerged that ultimately dominated early barley cultivation. Mutations in a single gene called SIX-ROWED SPIKE 1 (VRS1) have been identified as responsible for this important developmental switch. In two-rowed types, VRS1 mRNA is expressed in progenitor cells of the lateral spikelets which remain sterile presumably because VRS1 protein represses expression of genes that are required for development of 'lateral fertility'. Inactivating VRS1 via mutation would de-repress expression of lateral fertility genes, resulting in a six-rowed spike. While VRS1 is core to this process, we also know from historical studies with barley mutants that at least 11 different SIX-ROWED SPIKE genes influence the degree of fertility of the lateral spikelets. For example, we recently identified SIX-ROWED SPIKE 5 (VRS5), and showed that different versions of this gene (that we call 'alleles') are always paired with different versions of VRS1 in commercial two- and six- rowed barleys. This pairing is important because in lines that have the six-row version of VRS1 (denoted as vrs1), a two-row VRS5 allele (Vrs5) causes the development of small grain from the lateral spikelets. In contrast, the six-row version of VRS5 (vrs5) causes the lateral spikelets to develop fully, with important consequences on yield. This observation demonstrates that getting the correct combination of alleles at VRS genes is extremely important. While mutant studies have identified many VRS genes, we recently showed that natural variation in only four genes is associated with determining whether current elite UK barley cultivars are genetically optimal two- or six-row-types. As expected, one of these was VRS1 and another VRS5. We recently identified the third gene as VRS3 and are trying to identify the fourth, which does not coincide with the location of any of the eleven VRS mutants. In parallel, VRS4 has been identified by German collaborators. While we now know these genes are intrinsically linked by their involvement in the developmental pathway that restores fertility to a nascent floral organ (i.e. the lateral spikelets) at the moment we have no idea if or how these components interact, what other genes/proteins are involved or how six-rowed types evolved over the 10,000 years since the domestication of the species. These are the issues we plan to address in this project. We believe that a better understanding of this fundamental developmental process will provide insights into how we can exploit variation in genes controlling plant morphology and architecture to ultimately improve plant yield.