Three ancient hormonal cues co-ordinate shoot branching in a moss.
Three ancient hormonal cues co-ordinate shoot branching in a moss.
复制标题
DOI：
10.7554/elife.06808
复制
发表时间：
2015-03-25
期刊：
影响因子：
7.7
通讯作者：
Harrison CJ
中科院分区：
文献类型：
--
作者：
Coudert Y;Palubicki W;Ljung K;Novak O;Leyser O;Harrison CJ
枝条分枝是植物构型的主要贡献者，在开花植物的孢子体和苔藓配子体中独立进化。对分枝的机制理解在很大程度上局限于拟南芥等开花植物，这些植物具有最近的进化起源。我们发现，在配子体枝条中，侧枝是通过将表皮细胞重新指定为分枝的首字母而产生的。一个协调多叶茎尖活动的简单模型可以解释分枝模式，三个已知的和古老的孢子体分枝激素调节因素相互作用，产生分枝模式-生长素、细胞分裂素和斯特里内酯。枝条构型所需的生长素运输方式是与已知的孢子体途径的关键分歧点。尽管PIN介导的基瓣生长素运输调节开花植物的分枝模式，但在Physcomitrella中情况并非如此，需要双向运输才能产生真实的分枝模式。实验表明，细胞胞间连结是一种潜在的转运机制。DOI：http://dx.doi.org/10.7554/eLife.06808.001大多数陆地植物都有形成枝条的枝条，植物可以调节它们何时何地生长这些枝条，以最好地利用它们的环境。有花的植物和更古老的苔藓都有分枝的枝条，但这两类植物进化成了相互独立的这种生长方式。大多数关于枝条分枝的研究都集中在开花植物上，所以分枝在苔藓中是如何起作用的还不太清楚。三种植物激素--生长素、细胞分裂素和内酯--控制着开花植物的枝条分枝。生长素沿着植物的主枝向下移动，以防止新的分枝形成。这种运动由PIN蛋白和其他几个蛋白质家族控制。另一方面，细胞分裂素促进新枝的生长；而斯特里内酯可以促进或抑制枝条的分枝，这取决于生长素在植物周围的移动方式。Coudert，Palubicki等人。研究了一种名为Physcomitrella patens的苔藓物种的枝条分枝。实验表明，主枝外表面的细胞基本上被重新编程，成为所谓的“分枝首字母”，然后发育成新的分枝。接下来是Coudert，Palubicki等人。建立了一个计算模型，能够模拟苔藓中的枝条分枝模式。进一步的实验支持了该模型的预测。Coudert，Palubicki等人。研究发现，与开花植物一样，主茎顶端的生长素抑制苔藓的分枝，而细胞分裂素促进分枝。实验还表明，马立内酯抑制了枝条的分枝，但其作用仅限于枝条的根部。该模型预测，与开花植物不同，生长素必须在苔藓枝条中双向流动，才能产生观察到的枝条分枝模式。此外，实验表明，PIN蛋白和另一组控制生长素运动的蛋白质并不调节苔藓中的枝条。相反，生长素似乎可以通过连接一个苔藓细胞和另一个苔藓细胞的微观通道进行移动。S等人的发现表明，开花植物和苔藓都已经进化到使用相同的三种激素来控制枝条分枝，但这些激素以不同的方式相互作用。下一步的关键将是通过控制细胞之间通道的打开来找出生长素在苔藓枝条分枝过程中的运输方式。另一个挑战将是找出激素如何控制枝条初始细胞活动的准确细节。doi：http://dx.doi.org/10.7554/eLife.06808.002
Shoot branching is a primary contributor to plant architecture, evolving independently in flowering plant sporophytes and moss gametophytes. Mechanistic understanding of branching is largely limited to flowering plants such as Arabidopsis, which have a recent evolutionary origin. We show that in gametophytic shoots of Physcomitrella, lateral branches arise by re-specification of epidermal cells into branch initials. A simple model co-ordinating the activity of leafy shoot tips can account for branching patterns, and three known and ancient hormonal regulators of sporophytic branching interact to generate the branching pattern- auxin, cytokinin and strigolactone. The mode of auxin transport required in branch patterning is a key divergence point from known sporophytic pathways. Although PIN-mediated basipetal auxin transport regulates branching patterns in flowering plants, this is not so in Physcomitrella, where bi-directional transport is required to generate realistic branching patterns. Experiments with callose synthesis inhibitors suggest plasmodesmal connectivity as a potential mechanism for transport. DOI: http://dx.doi.org/10.7554/eLife.06808.001 Most land plants have shoots that form branches and plants can regulate when and where they grow these branches to best exploit their environment. Plants with flowers and the more ancient mosses both have branching shoots, but these two groups of plants evolved to grow in this way independently of each other. Most studies on shoot branching have focused on flowering plants and so it is less clear how branching works in mosses. Three plant hormones—called auxin, cytokinin and strigolactone—control shoot branching in flowering plants. Auxin moves down the main shoot of the plant to prevent new branches from forming. This movement is controlled by the PIN proteins and several other families of proteins. On the other hand, cytokinin promotes the growth of new branches; and strigolactone can either promote or inhibit shoot branching depending on how the auxin is travelling around the plant. Coudert, Palubicki et al. studied shoot branching in a species of moss called Physcomitrella patens. The experiments show that cells on the outer surface of the main shoot are essentially reprogrammed to become so-called ‘branch initials’, which will then develop into new branches. Next, Coudert, Palubicki et al. made a computational model that was able to simulate the pattern of shoot branching in the moss. Further experiments supported the predictions made by the model. Coudert, Palubicki et al. found that, as in flowering plants, auxin from the tip of the main shoot suppresses branching in the moss, and cytokinin promotes branching. The experiments also showed that strigolactone inhibits shoot branching, but its role is restricted to the base of the shoots. The model predicts that, unlike in flowering plants, auxin must flow in both directions in moss shoots to produce the observed patterns of shoot branching. Also, the experiments suggest that the PIN proteins and another group of proteins that control the movement of auxin do not regulate shoot branching in moss. Instead, it appears that auxin may move through microscopic channels that link one moss cell to the next. Coudert, Palubicki et al.'s findings suggest that both flowering plants and mosses have evolved to use the same three hormones to control shoot branching, but that these hormones interact in different ways. One key next step will be to find out how auxin is transported during shoot branching in moss by manipulating the opening of the channels between the cells. A further challenge will be to find out the precise details of how the hormones control the activity of the branch initial cells. DOI: http://dx.doi.org/10.7554/eLife.06808.002