Faculty of Veterinary and Agriculture, The University of Melbourne, Parkville, 3010, Australia.
Division of Plant Sciences, The James Hutton Institute, Invergowrie, Dundee, DD2 5DA, Scotland, UK.
Theor Appl Genet. 2022 Apr;135(4):1263-1277. doi: 10.1007/s00122-022-04029-8. Epub 2022 Feb 22.
Grain disarticulation in wild progenitor of wheat and barley evolved through a local duplication event followed by neo-functionalization resulting from changes in location of gene expression. One of the most critical events in the process of cereal domestication was the loss of the natural mode of grain dispersal. Grain dispersal in barley is controlled by two major genes, Btr1 and Btr2, which affect the thickness of cell walls around the disarticulation zone. The barley genome also encodes Btr1-like and Btr2-like genes, which have been shown to be the ancestral copies. While Btr and Btr-like genes are non-redundant, the biological function of Btr-like genes is unknown. We explored the potential biological role of the Btr-like genes by surveying their expression profile across 212 publicly available transcriptome datasets representing diverse organs, developmental stages and stress conditions. We found that Btr1-like and Btr2-like are expressed exclusively in immature anther samples throughout Prophase I of meiosis within the meiocyte. The similar and restricted expression profile of these two genes suggests they are involved in a common biological function. Further analysis revealed 141 genes co-expressed with Btr1-like and 122 genes co-expressed with Btr2-like, with 105 genes in common, supporting Btr-like genes involvement in a shared molecular pathway. We hypothesize that the Btr-like genes play a crucial role in pollen development by facilitating the formation of the callose wall around the meiocyte or in the secretion of callase by the tapetum. Our data suggest that Btr genes retained an ancestral function in cell wall modification and gained a new role in grain dispersal due to changes in their spatial expression becoming spike specific after gene duplication.
野生小麦和大麦祖先中的籽粒分离是通过局部重复事件进化而来的，然后由于基因表达位置的变化而产生新的功能化。谷物驯化过程中最重要的事件之一是失去了籽粒自然传播的模式。大麦籽粒的传播受两个主要基因 Btr1 和 Btr2 控制，它们影响离解区细胞壁的厚度。大麦基因组还编码 Btr1 样和 Btr2 样基因，它们被证明是祖先拷贝。虽然 Btr 和 Btr 样基因是非冗余的，但 Btr 样基因的生物学功能尚不清楚。我们通过调查 212 个公开可用的转录组数据集在不同器官、发育阶段和胁迫条件下的表达谱，探索了 Btr 样基因的潜在生物学作用。我们发现 Btr1 样和 Btr2 样基因仅在减数分裂前期 I 的减数分裂中期的未成熟花药样本中表达。这两个基因的相似且受限的表达谱表明它们参与了共同的生物学功能。进一步的分析显示，141 个基因与 Btr1 样共表达，122 个基因与 Btr2 样共表达，其中 105 个基因共同表达，支持 Btr 样基因参与共同的分子途径。我们假设 Btr 样基因通过促进围绕减数分裂细胞的胼胝质壁的形成或通过绒毡层分泌果胶酶在花粉发育中发挥关键作用。我们的数据表明，Btr 基因在细胞壁修饰中保留了祖先的功能，并由于基因复制后其空间表达在穗部变得特异，从而获得了在籽粒传播中的新功能。
