Control of seed size and yield by vernalisation

英国冬季油菜(WOSR)种植的一个主要问题是农场产量的年际波动很大，从每公顷3.0吨到3.9吨不等。天气和气候被认为是导致产量不稳定的关键因素，而气候变化可能是目前英国农业产量平台期的一个因素。因此，培育和选择适应不断变化的环境的新品种被广泛认为是英国农业的关键长期目标。针对这一努力，需要了解天气变化影响农场产量的精确生物学机制。在英国和北欧，所谓的“冬季”高产作物与春季作物的不同之处在于，它们需要在开花前经历一段长时间的冬季寒冷，这一过程被称为春化。虽然春化对开花的影响已经知道很多年了，但在这里我们第一次展示了春化在控制种子大小方面有更重要的作用。我们表明，来自春化程度较强的植物的种子比春化程度较弱的植物的种子大30%左右，而且这种大小的增加在果实或种子数量上没有任何损失。这些影响很大，足以解释英国农场观察到的30%的产量年际变化的很大一部分。此外，我们提供了新的证据表明，在非常精确的23天期间的冬季寒冷与英国油菜籽产量高度相关，这表明在景观尺度上春化可能对WOSR作物的产量表现很重要。一个关键的转录因子基因，开花基因C(FLC)，在冬季之前高度表达，在寒冷的天气中由于抑制染色质标记的积累而逐渐沉默。FLC在叶片和茎顶端分生组织中的表达控制着开花，但FLC也在种子中强烈表达，以前认为它与种子活力有关。另一方面，种子的大小主要由受精后种皮的膨胀控制，为胚胎和胚乳的生长创造了空间。我们的初步研究表明，在油菜中，FLC和第二个基因生长素反应因子2(ARF2)都可以在遗传上与春化控制种子大小有关。此外，在线基因组规模的数据集表明，ARF2很可能是Flc的直接靶标。在本提案中，我们将阐明春化控制种子大小的机制，并研究这一过程在WOSR田间产量变化中的重要性。我们的初步分析揭示了这一机制的一个非常强有力的候选者，我们的实验计划旨在详细研究这一点。利用JIC实验农场，我们将测试冬季寒冷是否通过影响种子大小来影响WOSR产量，以及春化和种子发育的关键分子事件如何在真实的田间场景中展开。通过在FLC和ARF2基因座携带遗传变异的品系一直到成熟期，我们将直接测试12月上旬的温度是否通过涉及这两个基因的机制影响油菜产量参数。一个目标是确定FLC和ARF2的新组合，这些组合在春化较弱的情况下仍保持较大的种子大小。然后，育种者可以使用这些等位基因的标记来选择产量表现更强劲的新品种，从而改善温暖的冬季对英国农业表现的一个重要负面影响。

A major problem with UK winter oilseed rape (WOSR) cultivation is the large inter-annual fluctuation in on-farm yields, varying from around 3.0 to 3.9 tonnes per hectare. Weather and climate are known to be critical factors in this yield instability, and climate change may be a factor in the current 'yield plateau' in UK agriculture. For this reason breeding and selection of new varieties suited to changing environments is widely appreciated to be a key long-term goal for UK agriculture. Targeting this effort requires an understanding of the precise biological mechanisms through which weather variation influences yield on farms. It is here that this proposal breaks new ground.In the UK and Northern Europe high yielding so-called 'winter' crops are distinguished from spring crops by their requirement for a period of prolonged winter cold before flowering, a process known as vernalisation. While the effect of vernalisation on flowering has been known for many years, here we show for the first time that vernalisation has a further major role in the control of seed size. We show that seeds from more strongly vernalised plants are around 30% larger than seeds from more weakly vernalised plants, and this size increase comes without any penalty in fruit or seed number. These effects are large enough to account for a substantial fraction of the 30% inter-annual variation in yield observed on farms in the UK. In addition, we provide new evidence that winter cold during a very precise 23-day period is highly correlated to UK rapeseed yields, suggesting that on a landscape scale vernalisation may be important for WOSR crop yield performance.The molecular mechanism underlying the vernalisation process is understood in detail. A key transcription factor gene, FLOWERING LOCUS C (FLC), is highly expressed before winter and is gradually silenced during the experience of cold weather by the accumulation of repressive chromatin marks. FLC expression in leaves and the shoot apical meristem controls flowering, but FLC is also strongly expressed in seeds where it has previously been implicated in seed vigour. Seed size on the other hand is controlled primarily by the expansion of the seed coat that occurs after fertilisation, creating the space into which the embryo and endosperm grow. Our preliminary study shows that in rapeseed both FLC and a second gene AUXIN RESPONSE FACTOR 2 (ARF2), a known seed size regulator in Arabidopsis, can both be genetically linked to the control of seed size by vernalisation. Furthermore, online genomic scale datasets show that ARF2 is likely a direct target of FLC.In this proposal we will elucidate the mechanism by which vernalisation controls seed size and examine the importance of this process in on-farm yield variation in WOSR. Our preliminary analysis has revealed a very strong candidate for this mechanism and our experimental programme is designed to investigate this in detail. Using the JIC experimental farm we will test whether winter cold affects WOSR yield by affecting seed size, and how the key molecular events of vernalisation and seed development unfold in a real field scenario. By taking lines carrying genetic variation at FLC and ARF2 loci through to maturity we will directly test whether temperature in early December affects rapeseed yield parameters through a mechanism involving these two genes. One goal is to identify new combinations of of FLC and ARF2 that maintain large seed size despite only weak vernalisation. Markers for these alleles can then be used by breeders to select new varieties with a more robust yield performance, ameliorating an important negative effect of warmer winters on UK agricultural performance.