近日，中科院遗传与发育生物学研究所储成才团队和福建中国农业科学院赵明富团队、遗传与发育生物学研究所李云海团队、武汉大学李绍清团队通过不同研究方法，阐述了生长调节因子受小RNA分子miR396的抑制，会影响水稻籽粒的大小和数量。三篇独立论文均于12月22日凌晨在线发表于《自然—植物学》期刊。

   在其中一项研究中，李绍清团队研究了杂交水稻稻穗数量比其父本和母本多的原因。他们发现，杂交水稻中的miR396表达受到抑制，因此解除了对由其调控的生长因子六(GRF6)的抑制。研究发现，GRF6表达的增加激活了一种植物激素的生物合成与信号传递，这种激素负责促进穗的形成。

   在另外两项研究中，储成才、赵明富等人则报告了两种形式的生长因子四(GRF4)，都能显著增加籽粒重量。研究发现这两种GRF4都包含突变，可以让它们对miR396的抑制不敏感。储成才团队发现，GRF4表达的增加会激活另一种类型的植物激素反应，从而进一步增强籽粒发育并增加籽粒大小。李云海团队则发现，GRF4也通过与转录共激活因子(帮助激活基因表达的蛋白质)的互动增加籽粒的大小和重量。

   三项研究表明，miR396和生长因子模块可通过多个分子通路调控谷物产量，尽管GRF6与GRF4都受到miR396的调控，这两者增加谷物产量的方式是不同的。该研究有助于指导未来高产水稻品种的选育。

   原文链接：Control of grain size and rice yield by GL2-mediated brassinosteroid responses

   原文摘要：Given the continuously growing population and decreasing arable land, food shortage is becoming one of the most serious global problems in this century1. Grain size is one of the determining factors for grain yield and thus is a prime target for genetic breeding2,3. Although a number of quantitative trait loci (QTLs) associated with rice grain size have been identified in the past decade, mechanisms underlying their functions remain largely unknown4,5. Here we show that a grain-length-associated QTL, GL2, has the potential to improve grain weight and grain yield up to 27.1% and 16.6%, respectively. We also show that GL2 is allelic toOsGRF4 and that it contains mutations in the miR396 targeting sequence. Because of the mutation, GL2 has a moderately increased expression level, which consequently activates brassinosteroid responses by upregulating a large number of brassinosteroid-induced genes to promote grain development. Furthermore, we found that GSK2, the central negative regulator of rice brassinosteroid signalling, directly interacts with OsGRF4 and inhibits its transcription activation activity to mediate the specific regulation of grain length by the hormone. Thus, this work demonstrates the feasibility of modulating specific brassinosteroid responses to improve plant productivity.

doi:10.1038/nplants.2015.195

   原文链接：Regulation of OsGRF4 by OsmiR396 controls grain size and yield in rice

   原文摘要：An increase in grain yield is crucial for modern agriculture1. Grain size is one of the key components of grain yield in rice and is regulated by quantitative trait loci (QTLs)2,3. Exploring new QTLs for grain size will help breeders develop elite rice varieties with higher yields3,4. Here, we report a new semi-dominant QTL for grain size and weight (GS2) in rice, which encodes the transcription factor OsGRF4 (GROWTH-REGULATING FACTOR 4) and is regulated by OsmiR396. We demonstrate that a 2 bp substitution mutation in GS2 perturbs OsmiR396-directed regulation of GS2, resulting in large and heavy grains and increased grain yield. Further results reveal that GS2 interacts with the transcription coactivitors OsGIF1/2/3, and overexpression of OsGIF1 increases grain size and weight. Thus, our findings define the regulatory mechanism of GS2, OsGIFs and OsmiR396 in grain size and weight control, suggesting this pathway could be used to increase yields in crops.

doi:10.1038/nplants.2015.203

   原文链接：Blocking miR396 increases rice yield by shaping inflorescence architecture

   原文摘要：Strategies to increase rice productivity to meet the global demand have been the main concern of breeders around the world. Although a growing number of functional genes related to crop yield have been characterized, our understanding of its associated regulatory pathways is limited. Using rice as a model, we find that blocking miR396 greatly increases grain yield by modulating development of auxiliary branches and spikelets through direct induction of the growth regulating factor 6 (OsGRF6) gene. The upregulation of OsGRF6 results in the coordinated activation of several immediate downstream biological clades, including auxin (IAA) biosynthesis, auxin response factors, and branch and spikelet development-related transcription factors. This study describes a conserved microRNA (miRNA)-dependent regulatory module that integrates inflorescence development, auxin biosynthesis and signalling pathways, and could potentially be used in engineering high-yield crop plants.