Establishing a chromosome map for Spirodela polyrhiza, chromosome homeology and karyotype evolution within the aquatic, largely asexual Lemnoideae, a basic monocot group of potential economic importance

扁桃亚科是扁桃目单子叶植物的一个单系亚科，是一种体积小，表型简单的自由漂浮水生生物，具有非常快的营养繁殖。因此，一些物种被认为是有效的生物质生产，以产生生物燃料，喂养牲畜和（同时）清洁废水。柠檬亚科包括5属37种。对多根螺旋体的基因组进行了测序，作为柠檬总科基因组的参考。我们已经证实该物种的基因组大小较小（158 Mbp/1C），有2n=40条染色体。本研究的目的是建立多根葡萄的遗传组成、多样性和进化的核型，以及所有五个属的代表物种，显示不同的基因组大小和染色体互补。由于其有性繁殖的罕见性和遗传图谱的缺乏，需要通过原位杂交的方法将已确认并部分校正的多根藤基因组序列排列为20个连锁群。然后，基于染色体特异性多根草BAC池的比较染色体绘制，将揭示多根草和其他Lemnoideae物种自然克隆之间的染色体同源性、核型多样性和进化（染色体间和染色体内重排、倍体突变），这些物种显示出不同的基因组大小和/或染色体数目，以及不同的体型和新化程度。如果采用其他技术，这种比较会复杂得多。该方法将进一步阐明浮萍无性系间的遗传多样性，为浮萍无性系的应用研究提供可靠依据。

Lemnoideae, a monophyletic subfamily within the monocot order Alismatales, are small and phenotypically simple free-floating aquatic organisms with very fast vegetative propagation. Therefore, some species are considered for efficient biomass production to generate biofuel, to feed livestock and (simultaneously) to clean waste water. The Lemnoideae comprise 5 genera of together 37 species. The genome of Spirodela polyrhiza has been sequenced as a reference for Lemnoideae genomes. We have confirmed the small genome size (158 Mbp/1C), and 2n=40 chromosomes for this species. The aim of the proposal is to establish the genetic composition, diversity and evolution of karyotypes for S. polyrhiza, and for representative species of all five genera, displaying variable genome sizes and chromosome complements. Because of rare sexual propagation and lacking genetic maps, the genomic contigs (which we confirmed and partially corrected) of S. polyrhiza need to be arranged into 20 linkage groups by means of in situ hybridisation. Then, comparative chromosome painting, based on chromosome-specific S. polyrhiza BAC pools, will reveal chromosome homeology and karyotype diversity and evolution (inter- and intrachromosomal rearrangements, ploidy mutations) between natural clones of S. polyrhiza and other Lemnoideae species that display different genome sizes and/or chromosome numbers as well as different body size and degree of neotenisation. Such comparison would be much more intricate by other techniques. Our approach will elucidate the genetic diversity between vegetative clones of duckweeds and provide a reliable basis for application-oriented research on this under-investigated potential crops.