Floral success depends on its backbone—first insights into rachis growth and development and its implications on wheat floret fertility and grain number

花序是小麦（小麦属）最突出的部分。厂因此，自农业诞生以来，花序结构一直处于不断的选择之下，并且由于其对潜在谷物产量的影响而在现代育种中经久不衰。虽然古老的小麦形式，如野生和驯化的二粒小麦显示出长的矛形穗，但由于短轴（穗轴）节间，目前的小麦品种表现出短而紧凑的穗表型。以往的研究表明，小麦穗形向紧凑方向的进化主要是由于对易弯、不脆等驯化关键性状的间接选择。然而，穗轴生长本身对谷物产量构成因素的发展的影响仍然难以捉摸。轴基本上是生殖发育的骨干;它不仅携带所有的花结构，所有的供应（即，花的生长和发育所需的水分、养分、同化物也必须通过它。因此，它的解剖特征和模式至少在某种程度上决定了基本的农艺性状，如粒数和粒重。在这里，我们建议使用自然变异的历史轨迹中选择在分歧的硬质小麦（~7000-7500年前），研究发展起源的轴生长的变化，这反过来又如何影响粮食产量潜力。利用正向遗传的方法，我们已经定位了这个特定的基因座调节穗长~3.5 Mbp的长臂上的小麦染色体4A。 表型分析表明，穗，与野生二粒小麦等位基因在这个位点，产生更长的轴节间，但同样更广泛的轴nodes.Interestingly，我们发现轴节间长度和在每个小穗发育的籽粒数之间呈正相关。我们假设，整体轴的增长包括轴维管束数量或直径增加，以前显示，以促进小花生育力，通过增加花同化物供应和粮食集。这个想法似乎非常令人兴奋，并可能揭示丰富的等位基因剧目野生二粒小麦花序结构的塑造。 因此，在拟议的研究项目中，我们将专注于这个有前途的，未探索的联系轴生长，同化物分配和小花发育的发育遗传学，发现新的小麦粒数决定机制。

The inflorescence is the most prominent part of the wheat (Triticum sp.) plant. As such, inflorescence architecture has been under constant selection since the dawn of agriculture and is enduring in modern breeding due to its the impact on potential grain yield. While ancient wheat forms like wild and domesticated emmer display a long spear-shaped spike, current wheat varieties exhibit a short and compact spike phenotype due to short rachis (spike axis) internodes. Previous studies have indicated that the evolution of wheat spike shape towards compactness mainly results from indirect selection of key domestication traits like free-threshing and non-brittleness. However, the effect of rachis growth per se on the development of grain yield components remains elusive. The rachis is essentially the backbone for reproductive development; it not only carries all floral structures, all supply (i.e., water, nutrients, assimilates) for floral growth and development must also pass through it. Therefore, its anatomical features and patterning determine, at least to some degree, essential agronomical traits like grain number and grain weight. Here, we propose to use natural variation in a historical locus selected during the divergence of durum wheat (~7000-7500 years ago) to study the developmental origin of variation in rachis growth and how this, in turn, affects grain yield potential. Using a forward genetic approach, we have mapped this rachis-specific locus regulating spike length to ~3.5 Mbp on the long arm of wheat chromosome 4A. Phenotypic analysis showed that spikes, associated with the wild emmer allele at this locus, produce longer rachis internodes but similarly broader rachis nodes.Interestingly, we found a positive correlation between rachis internode length and the number of grains developed in each spikelet. We hypothesize that overall rachis growth includes increased rachis vascular bundle numbers or diameters, previously shown to promote floret fertility by increasing floral assimilate supply and grain set. This idea appears very exciting and may uncover the rich allelic repertoire of wild emmer for shaping wheat inflorescence architecture. Therefore, in the proposed research project, we will focus on the developmental genetics of this promising, unexplored link between rachis growth, assimilate allocation and floret development to discover novel grain number determination mechanisms in wheat.