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。迫切需要碳中性的可再生能源(即不以二氧化碳的形式净排放碳)。1999年，可再生能源占英国总发电量的约3%。政府已经制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都需要大幅提高，包括风能、太阳能和水力发电，以及来自种植“生物质作物”的能源。生物质作物是多年生、快速生长的物种，能够迅速积累可燃物质(如茎和木材)。生物质被收获并燃烧以取暖或发电。由于燃烧时释放的二氧化碳在接下来的几年增长中被重新吸收，它们是碳中性的，也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。它们是在短轮换丛林(SRC)周期中生长的，在这种周期中，种植的插穗在生长的第一年后被砍掉，切割的树桩(凳子)被允许重新萌发，以提供多个枝条。3年后收获这些丛林嫩枝，以提供第一批生物量收获，SRC循环将继续20年。高产对于SRC柳树来说是经济的关键，尽管有高产品种可用，但为了生产英国目标所需的生物量，已经提出了产量翻一番的建议。因此，提高生物量产量是当前英国柳树育种的主要目标。柳树的采伐能力是生物质生产的关键。柳树物种的复制能力不同，但这些差异的基因控制尚不清楚。此外，茎多(细)的柳树和粗(细)茎少的柳树都能高产。这使得育种者很难选择高产的生物量类型，也很难预测不同柳树之间杂交的结果。一些发育研究试图了解这些差异的本质，并提出它们与通过顶端优势保持休眠的预先存在的芽的数量、位置和生长有关。对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，有大量关于芽形成和芽活动的调控知识。也有明确的证据表明，这些调控机制在高等植物中是保守的，包括树木。在这个合作项目中，我们将利用拟南芥的先进知识，研究柳树含铜量的遗传调控。在前期工作中，我们已经证明了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有共同的联系。我们现在将测试这些假设，即它们参与决定柳树的花蕾行为，从而复制潜力。我们将首先关注控制拟南芥分枝的基因，例如更腋下分枝(Max)家族，但我们也将研究在作物玉米中决定分枝的关键基因--teosinte分支(TCP家族)，该基因在拟南芥中也已被研究过。我们将利用我们在拟南芥中的知识来测试假说，即柳树的花蕾数量和花蕾行为可能受到不同的基因控制，并帮助识别其他可以影响含铜量的基因。我们的总体目标将是建立一个关于丛枝柳枝条数量和枝条生长的遗传调控模型，并为相关基因提供标记，从而为育种中选择改良的生物质柳树提供便利。

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 are able rapidly to 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.