报告题目：Strigolactones: (rhizosphere) signalling molecules with surprising biological activities

报 告 人：Prof. dr. Harro J. Bouwmeester,Wageningen University, the Netherlands

报告时间：2010年9月27日，上午9:00

报告地点： B210报告厅

联 系 人：熊国胜

联系电话：64806008

Abstract

During evolution, plants have adapted an ecological balance with their associates, competitors, predators and pests. Keeping this balance intact is an active process during which the plant needs to respond to many different stimuli in order to survive. For example, plants have developed an array of physiological and biochemical responses to phosphate deprivation. One of these responses is the formation of symbiotic associations of plant roots with arbuscular mycorrhizal (AM) fungi. AM fungi colonize the root cortex to obtain carbon from their host while assisting the plant in phosphate acquisition. Hyphal branching in mycorrhiza, a growth characteristic preceding colonisation of the plant root, is stimulated by compounds called strigolactones which are present in the plant root exudate. Strigolactone production is specifically increased in plants exposed to low phosphate thereby actively inviting mycorrhizal colonization. Unfortunately, strigolactones also stimulate the germination of root parasitic plants, the witchweeds and broomrapes. Only upon perception of the presence of a host through its strigolactone production, seeds of these parasites germinate and attach to the roots of many plant species such as several legumes, maize, tomato, sunflower, hemp and tobacco. In contrast to a mutualistic symbiotic relationship, where both partners benefit from the affiliation through an exchange of resources, the host is heavily exploited by a parasitic plant and suffers strongly from the interaction because it is robbed from its assimilates, water and nutrients. 

In addition to these functions in the rhizosphere, strigolactones or their metabolites were recently shown to be a novel class of plant hormones inhibiting shoot branching/tillering. It has been hypothesized that the inhibitory effect of strigolactones on axillary bud outgrowth is the result of a negative effect on auxin transport capacity. Also here there is a relation with phosphate: phosphate starvation-induced strigolactone production is responsible for the reduction in the number of shoot branches during limiting phosphate conditions. Because auxin and auxin transport play such crucial roles in defining root system architecture we also investigated the contribution of strigolactones to root developmental processes and found that strigolactones affect lateral root development. We hypothesize that endogenous strigolactones are responsible for the rapid development and outgrowth of lateral roots of plants growing under phosphate limiting conditions. Therefore, strigolactones do not only have a direct effect on the rhizosphere as being part of root exudates, but also through their function as plant hormone in root developmental processes inside the plant.

Because of their crucial role in rhizosphere communication and regulation of plant development, the regulation of strigolactone biosynthesis is of great interest. The genes so far identified to be involved in strigolactone biosynthesis and signaling - using highly branched/tillered mutants: Arabidopsis max (more axilary branching), rice dwarf or htd (high tillering dwarf), Petunia dad (decreased apical dominance) and pea rms (ramosus) - will be discussed.