Accelerating breeding for biomass yield in short rotation coppice willow by exploiting knowledge of shoot development in Arabidopsis

在英国，超过四分之三的能源来自燃烧化石燃料。然而，这种做法有两个问题。首先，二氧化碳和其他温室气体的相关排放正在导致全球变暖，其次，英国的化石燃料供应正在枯竭。目前迫切需要碳中性（即不以二氧化碳形式净释放碳）的可再生能源。1999年，可再生能源占英国总发电量的约3%。政府已经设定了具有挑战性的目标，到2050年将这一比例提高到60%，并认识到所有可再生能源的贡献将需要大幅提高，包括风能、太阳能、水力发电和种植“生物质作物”的能源。生物质作物是多年生、快速生长的物种，它们能够迅速积累可燃物质（如茎和木材）。生物质的收获和燃烧产生热量或电力。由于燃烧释放的二氧化碳在随后几年的生长过程中被重新吸收，它们是碳中性的，并且需要很少的化学投入。柳树是温带地区最先进的生物质作物之一。它们以短轮制（SRC）循环方式生长，在种植的插枝在生长的第一年后被剪掉，而被剪掉的树桩（茎）被允许重新发芽以提供多枝。这些小灌木林的枝条在3年后收获，以提供第一次生物量收获，SRC循环将继续进行20年。高产对SRC柳树的经济效益至关重要，尽管有高产品种，但为了生产英国目标所需的生物量，建议将产量提高一倍。因此，提高生物量产量是当前英国柳树育种的主要目标。柳树的适应能力是生物量生产的关键。不同种类的柳树具有不同的适应能力，但这些差异的遗传控制尚不清楚。而且，茎多（细）的柳和茎粗少的柳产量都很高。这使得育种者难以选择高产生物量类型或预测不同柳树之间杂交的结果。一些发育研究试图理解这些差异的本质，并提出它们与顶端优势保持休眠状态的预先存在的芽的数量、位置和生长有关。对于柳树中这些过程的遗传控制知之甚少，但在模式植物拟南芥中，关于芽形成和芽活性的调控有大量的知识。也有明确的证据表明，这些调节机制在包括树木在内的高等植物中是保守的。在这个合作项目中，我们将利用拟南芥的先进知识，研究柳树剪枝的遗传调控。在前期工作中，我们已经证明影响拟南芥分枝的基因存在于柳树中，并且这些基因在遗传上与生物量产量共同相关。我们现在将测试的假设，他们参与决定芽行为，从而在柳树的coping潜力。我们将首先关注控制拟南芥分支的基因，例如腋窝分支（MAX）家族，但我们也将研究teosintebranched （TCP家族），这是作物植物玉米中决定分支的关键基因，也在拟南芥中进行了研究。我们将利用我们在拟南芥方面的知识来检验柳树中芽数和芽行为可能受到不同遗传控制的假设，并帮助确定其他可能影响扦插的基因。我们的总体目标是建立一个连片柳树枝数和枝长遗传调控的模型，并为相关基因提供标记，从而为生物量改良柳树的育种选择提供依据。

Over three-quarters of our energy in the UK is derived from burning fossil fuels. However, there are two problems with this practice. Firstly, the associated emission of carbon dioxide and other greenhouse gases is causing global warming and, secondly, UK fossil fuel supplies are being depleted. Renewable sources of energy which are carbon-neutral, (i.e. no net release of carbon as carbon dioxide) are urgently needed. In 1999, renewable energy represented ~3% of total electricity generated in the UK. The government has set challenging targets for this to rise to 60% by 2050 and it recognised that the contributions from all renewable energy sources will need to be significantly boosted, including wind, solar and hydro-power and energy from growing 'biomass crops'. Biomass crops are perennial, fast growing species that they are able to rapidly accumulate combustible material (e.g. stems and wood). The biomass is harvested and burnt for heat or electricity. Since the carbon dioxide released on combustion is re-incorporated during the following years' growth, they are carbon-neutral and also require few chemical inputs. Willows are among the most advanced biomass crops in temperate regions. They are grown in short-rotation coppice (SRC) cycles, in which planted cuttings are cut back after the first year of growth and the cut stumps (stools) are allowed to re-sprout to provide multiple shoots. These coppice shoots are harvested 3 years later to provide the first biomass harvest and the SRC cycle is continued for a further 20 years. High yields are crucial for SRC willow to be economical and although high yielding varieties are available, a doubling of yield has been proposed in order to produce the biomass required for UK targets. Improving biomass yield is thus a major goal of current UK willow breeding. The coppicing ability of willow is key to biomass production. Willow species differ in their coppicing ability but the genetic control of these differences is not yet known. Moreover, willows with more (thin) stems and willows with few thick stems can both produce high yield. This makes it difficult for breeders to select for high yielding biomass types or predict the outcome of crosses between different willows. Some developmental studies have attempted to understand the nature of these differences and have suggested that they relate to the number, position and outgrowth of pre-existing buds kept dormant by apical dominance. Little is known about the genetic control of these processes in willows, but in the model plant Arabidopsis there is a substantial body of knowledge on the regulation of bud formation and bud activity. There is also clear evidence that these regulatory mechanisms are conserved across higher plants, including trees. In this collaborative project we will take advantage of the advanced knowledge in Arabidopsis, to investigate the genetic regulation of coppicing in willow. In preliminary work we have shown that genes affecting branching in Arabidopsis are present in willow and that these genes co-associate in inheritance with biomass yield. We will now test the hypotheses that they are involved in determining bud behaviour and thus coppicing potential in willow. We will start by focussing on genes controlling branching in Arabidopsis, e.g. the more axillary branching (MAX) family but we will also investigate teosinte-branched (TCP family) a key gene determining branching in the crop plant maize, which has also been investigated in Arabidopsis. We will use our knowledge in Arabidopsis to test the hypotheses that bud number and bud behaviour may be under different genetic control in willow and to help identify other genes that can affect coppicing. Our overall goal will be to build up a model of the genetic regulation of shoot number and shoot outgrowth in coppiced willows and to provide markers for the genes involved, and thus facilitate the selection of improved biomass willows in breeding.