大麦的花序，即穗，由不同数量的小穗组成。小穗长在坚固、扁平且蛇曲状的穗轴上，由两片护颖和一朵小花组成。三个小穗互生于穗轴的同一个节上。二棱大麦只有中间的一朵小花可育，两侧的两朵小花败育，从而使每个节位上只有一粒种子，穗子呈扁平状。六棱大麦的三联小穗都可育，造成穗上种子性状的不同，穗子呈圆形或管状。在六棱大麦中约三分之一的种子外形与二棱大麦一样是匀称的，其它的种子不匀称，即扭曲的。这些扭曲的种子是小穗两侧的小花发育而来的，其籽粒较小，比匀称的种子小13%-20%。通常，二棱大麦的分蘖数较多，种子较六棱大麦大且重；另一方面，六棱大麦的每穗粒数较多，这种补偿效应使得这两类大麦的产量潜力相似。
阐明棱形和小穗发育的遗传机理对于进一步提高大麦产量具有重要意义。经典遗传学已经克隆了5个控制大麦穗形态建成的基因，称为SIX-ROWED SPIKE (VRS)，其中4个被确认为转录因子。近日，英国邓迪大学的研究人员揭示了第5个关键基因VRS3的遗传调控机制。
研究表明，VRS3基因编码一个JmJC类的组蛋白H3K9me2/me3去甲基化酶，具有调控染色质状态的功能。表达调控网络研究发现，VRS3基因不仅参与其它VRS基因的互作，而且与胁迫响应、激素调控以及糖代谢相关。进一步地研究发现，将突变的vrs3等位基因与自然的VRS1和VRS5等位基因聚合能够显著增加侧花籽粒的大小和均称度。该研究成果有望应用于大麦产量和品质性状改良。
Nature Communications, 8: 936; 16 October 2017
Barley SIX-ROWED SPIKE3 encodes a putative Jumonji C-type H3K9me2/me3 demethylase that represses lateral spikelet fertility
Author
Hazel Bull, M. Cristina Casao, Monika Zwirek……Arnis Druka, Sarah M. McKim & Robbie Waugh*
Cell and Molecular Sciences, The James Hutton Institute; Divisionof Plant Sciences, School of Life Sciences, The University of Dundee at The James Hutton Institute, Scotland.
Abstract
The barley inflorescence (spike) comprises a multi-noded central stalk (rachis) with tri-partite clusters of uni-floretted spikelets attached alternately along its length. Relative fertility of lateral spikelets within each cluster leads to spikes with two or six rows of grain, or an intermediate morphology. Understanding the mechanisms controlling this key developmental step could provide novel solutions to enhanced grain yield. Classical genetic studies identified five major SIX-ROWED SPIKE (VRS) genes, with four now known to encode transcription factors. Here we identify and characterise the remaining major VRS gene, VRS3, as encoding a putative Jumonji C-type H3K9me2/me3 demethylase, a regulator of chromatin state. Exploring the expression network modulated by VRS3 reveals specific interactions, both with other VRS genes and genes involved in stress, hormone and sugar metabolism. We show that combining a vrs3 mutant allele with natural six-rowed alleles of VRS1 and VRS5 leads to increased lateral grain size and greater grain uniformity.
