Auxin as a key regulator of pod shatter in Arabidopsis and Brassica

All flowering plants produce fruit. Whereas we often think of fruit as tasty and nutritious food, the plants use them to protect and nurse the seed that will give rise to the next generation. Fruit occur in extremely diverse shapes and sizes among flowering plants. They range from the size of a grain of table salt to the giant pumpkins that can weigh more than 1000 pounds. Many of the underlying mechanisms, which control fruit development, are mediated by developmental regulators called hormones. These mechanisms are shared among different plant species, and it therefore makes sense to study them in a plant species, which has obvious advantages as a research tool - a so-called model plant. A model plant should grow from a single seed to produce fruit in a short period of time (within a month) and be relatively easy to grow. The small Arabidopsis plant has these advantages and we already know some of the key genetic components that control Arabidopsis fruit development. One of the most important crop species in the UK is oilseed rape that colours the landscape in bright yellow patches during spring and early summer. Oilseed rape produces seed with a high content of nutritious oil that we use mainly in cooking and frying. In recent years seed oils have also become increasingly popular as biofuels for cars, buses, and trucks and may some day substitute diesel and gasoline. Oilseed rape fruit dry out at maturity and open to allow their seed to be dispersed in a process called pod shatter. Unfortunately, all the fruit in the field do not dry out at the same time making it difficult for oilseed rape farmers to time their harvest and obtain all the seed. In fact, an average of 15-20% of the harvest is lost every year. This loss can reach 50% in years with particularly windy conditions or when wet weather delays harvest. Despite a remarkable size difference, fruit from Arabidopsis and oilseed rape are very similar and we know from work in Arabidopsis that the plant hormone auxin can inhibit the pod shattering process. In the proposed research project, we will both expand our knowledge of this mechanism in the model plant, Arabidopsis, and develop technology to reduce pod shatter in oilseed rape based on that knowledge. In conclusion, we believe that our work in will provide substantial benefits for both farmers and consumers, as well as for the environment.

Arabidopsis fruit are typical of fruit from the >3000 species of the Brassicaceae family and develop from the female reproductive tissue, the gynoecium. After fertilisation, patterning genes divide the developing fruit into three main parts: The valves, the replum, and the valve margins that form at the valve/replum border. At the valve margin a narrow file of dehiscence zone cells differentiates along the entire length of the fruit late in development, allowing the valves to detach from the replum and seed dispersal to occur by a mechanism called pod shatter. Recent results from my group have shown that the plant hormone, auxin, is a major player in regulating tissue formation in Arabidopsis fruit. These results indicate that local tissue-specific changes in auxin concentration controls pod shatter. Here we will investigate the role of auxin in fruit development further by driving the expression of auxin-modifying genes in various tissues of the fruit and by revealing how the flow of auxin is regulated during Arabidopsis fruit development. Brassica species are closely related to Arabidopsis and represent ideal candidates for model-to-crop approaches as they include important crop plants such as oilseed rape. Brassica plants also disperse their seed by pod shatter. Although this mechanism is an advantage in nature, unsynchronised pod shatter constitutes one of the biggest problems for oilseed rape farmers. Despite a remarkable size difference, the overall shape of Arabidopsis and Brassica fruit are highly similar suggesting that strategies to modify pod shatter in Arabidopsis may be readily transferable into various Brassicas. Here we will use knowledge from Arabidopsis on the role of auxin in fruit patterning to regulate specification of Brassica fruit tissues. This approach should allow us to develop distinct strategies for controlling pod shatter in Brassica with benefits for the UK economic competitiveness, farmers, the public and the environment.