Wheat TILLING mutants show that the vernalization gene VRN1 down-regulates the flowering repressor VRN2 in leaves but is not essential for flowering.
Wheat TILLING mutants show that the vernalization gene VRN1 down-regulates the flowering repressor VRN2 in leaves but is not essential for flowering.
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DOI：
10.1371/journal.pgen.1003134
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发表时间：
2012
期刊：
影响因子：
4.5
通讯作者：
Dubcovsky J
中科院分区：
文献类型：
--
作者：
Chen A;Dubcovsky J
小麦春化反应中的大多数自然变异是由MADS盒转录因子VERNALIZATION 1（VRN 1）的等位基因差异决定的。在冬季（春化）延长暴露于低温诱导VRN 1的表达，并促进顶端分生组织的生殖阶段的过渡。与其拟南芥同源物（APETALA 1）（主要在顶端分生组织中表达）相反，VRN 1在叶中也以高水平表达，但其在该组织中的功能尚不清楚。使用四倍体小麦株系与截断突变的两个同源拷贝的VRN 1（此后VRN 1无效突变体），我们证明了VRN 1在叶片中的核心作用是保持低转录水平的VRN 2开花抑制春化后。VRN 2的转录水平逐渐下调，在春化过程中的突变体和野生型基因型，但上调春化后，只有在vrn 1无效突变体。VRN 2的上调通过抑制FT的转录来延迟开花，FT是一种开花整合基因，其编码一种移动的蛋白，该蛋白从叶子运输到顶端分生组织以诱导开花。VRN 2在vrn 1无效突变体延迟开花中的作用通过使用双vrn 1-vrn 2无效突变体来证实，该双vrn 1-vrn 2无效突变体比vrn 1无效突变体提前两个月开花。这两种突变体都产生了正常的花和种子，表明VRN 1对小麦开花并不重要，这与目前的开花模型相矛盾。这一结果并没有削弱VRN 1在小麦开花季节性调节中的重要性。在冬季期间VRN 1的上调是维持VRN 2的低转录水平、加速叶片中FT的诱导以及调节春季的适时开花所必需的。我们的研究结果还表明，存在多余的小麦开花基因，可能为工程小麦品种更好地适应不断变化的环境提供新的目标。作物产量与开花时间密切相关，因此需要精确了解开花调控机制，以设计适应新环境或变化环境的品种。在小麦中，大多数开花时间的自然变化是由VERNALIZATION 1（VRN 1）决定的，VRN 1是一种负责顶端分生组织从营养阶段过渡到生殖阶段的基因。在冬季（春化）期间长期暴露在低温下会诱导VRN 1表达，从而促进春季开花。VRN 1在叶尖和叶中表达，但其在叶中的作用尚不清楚。使用两套VRN 1敲除突变体，我们证明了VRN 1在叶片中的核心作用是维持VRN 2开花抑制子的低转录水平，这允许产生启动开花所需的移动的FT蛋白（成花素）。这两组VRN 1敲除突变体开花都很晚，但最终产生了正常的花和种子，这表明VRN 1对小麦开花不是必需的。最后一个结果也证明了冗余开花基因的存在，可以为小麦开花时间的工程设计提供新的目标。
Most of the natural variation in wheat vernalization response is determined by allelic differences in the MADS-box transcription factor VERNALIZATION1 (VRN1). Extended exposures to low temperatures during the winter (vernalization) induce VRN1 expression and promote the transition of the apical meristem to the reproductive phase. In contrast to its Arabidopsis homolog (APETALA1), which is mainly expressed in the apical meristem, VRN1 is also expressed at high levels in the leaves, but its function in this tissue is not well understood. Using tetraploid wheat lines with truncation mutations in the two homoeologous copies of VRN1 (henceforth vrn1-null mutants), we demonstrate that a central role of VRN1 in the leaves is to maintain low transcript levels of the VRN2 flowering repressor after vernalization. Transcript levels of VRN2 were gradually down-regulated during vernalization in both mutant and wild-type genotypes, but were up-regulated after vernalization only in the vrn1-null mutants. The up-regulation of VRN2 delayed flowering by repressing the transcription of FT, a flowering-integrator gene that encodes a mobile protein that is transported from the leaves to the apical meristem to induce flowering. The role of VRN2 in the delayed flowering of the vrn1-null mutant was confirmed using double vrn1-vrn2-null mutants, which flowered two months earlier than the vrn1-null mutants. Both mutants produced normal flowers and seeds demonstrating that VRN1 is not essential for wheat flowering, which contradicts current flowering models. This result does not diminish the importance of VRN1 in the seasonal regulation of wheat flowering. The up-regulation of VRN1 during winter is required to maintain low transcript levels of VRN2, accelerate the induction of FT in the leaves, and regulate a timely flowering in the spring. Our results also demonstrate the existence of redundant wheat flowering genes that may provide new targets for engineering wheat varieties better adapted to changing environments. Crop yields are strongly associated with flowering time, therefore a precise understanding of the mechanisms involved in the regulation of flowering is required to engineer varieties adapted to new or changing environments. In wheat, most of the natural variation in flowering time is determined by VERNALIZATION1 (VRN1), a gene responsible for the transition of the apical meristem from the vegetative to the reproductive phase. Extended exposures to low temperatures during winter (vernalization) induce VRN1 expression, which promotes flowering in the spring. VRN1 is expressed in the apices and in the leaves, but its role in the leaves is not well understood. Using two sets of VRN1 knock-out mutants, we demonstrate that a central role of VRN1 in the leaves is to maintain low transcript levels of the VRN2 flowering repressor, which allows the production of the mobile FT protein (florigen) required to initiate flowering. Both sets of VRN1 knock-out mutants flowered very late but, eventually, produced normal flowers and seeds, which demonstrates that VRN1 is not essential for wheat flowering. This last result also demonstrates the existence of redundant flowering genes that could provide new targets for engineering flowering time in wheat.
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影响因子：
7.4
作者：
Hemming, Megan N.;Peacock, W. James;Trevaskis, Ben
通讯作者：
Trevaskis, Ben
影响因子：
3.1
作者：
Kinjo, Hiroko;Shitsukawa, Naoki;Murai, Koji
通讯作者：
Murai, Koji
影响因子：
4.9
作者：
Adam, Helene;Ouellet, Francois;Sarhan, Fathey
通讯作者：
Sarhan, Fathey
影响因子：
3.1
作者：
Dubcovsky, J;Chen, CL;Yan, LL
通讯作者：
Yan, LL
DOI：
10.1073/pnas.0903566106
发表时间：
2009-05-19
影响因子：
11.1
作者：
Oliver, Sandra N.;Finnegan, E. Jean;Trevaskis, Ben
通讯作者：
Trevaskis, Ben