A possible role of prolyl oligopeptidase during Linum usitatissimum (flax) seed development

Involvement of prolyl oligopeptidases (POPs) in the control of several mammalian peptide hormone signalling pathways has been studied extensively in recent years. POPs are ubiquitous enzymes, but little attention has been paid to understanding their function in plants. Using a cDNA-AFLP approach, two flax (Linum usitatissimum) POP ESTs were identified as being specifically expressed in the early stages of flax seed development. This specific expression was confirmed using real time RT-PCR and in situ hybridisation approaches. Seed expression of Arabidopsis POP genes was measured and showed no specificity. Comparison between results obtained with flax and Arabidopsis is discussed in order to address a hypothetic function for POPs during seed formation. These results provide the first insights into POP gene expression and hypothetical function in plants.     

Duplication and functional diversification of HAP3 genes leading to the origin of the seed-developmental regulatory gene, LEAFY COTYLEDON1 (LEC1), in nonseed plant genomes

The HAP3 gene encodes a subunit of the CCAAT-box-binding factor (CBF), a highly conserved trimeric activator that recognizes and binds the ubiquitous CCAAT promoter element with high affinity. Two types of HAP3 gene have been identified in plant genomes. The LEAFY COTYLEDON1 (LEC1)-type HAP3 genes encode a functionally specialized subunit of CBF, which is expressed specifically in developing seeds. In contrast, most non-LEC1-type HAP3 genes are expressed in various tissues. It has been proposed that the LEC1-type HAP3 genes originated from the duplication and functional divergence of non-LEC1-type HAP3 genes. However, it is not yet known when this duplication event took place or whether the LEC1-type HAP3 genes appeared at the same time as the origin of seed plants. Here we describe a comprehensive comparison of the duplication patterns of HAP3 genes in different plant genomes. We recognize a major expansion of the HAP3 gene family accompanying the origin and early diversification of land plants and postulate that retrotransposition and other mechanisms of gene duplication have been involved in the expansion of the plant HAP3 gene family. We provide evidence that the LEC1-type HAP3 genes originated in nonseed vascular plant genomes and demonstrate that they are inductively expressed under drought stress in nonseed plants. These genes, however, were recruited to a novel regulatory network in the early stages of seed plant evolution and steadily expressed during seed development and maturation.     

水稻MYB cDNA的克隆和表达分析

根据植物MYB类转录因子DNA结合功能域的保守区设计一对简并引物 ,以水稻根、小苗和未成熟种子中的RNA为材料 ,用RT PCR方法扩增出约 180bp的片段。序列分析表明 ,它们与MYB基因的保守区有很好的同源性。以未成熟种子中获得的这一 180bp片段作探针 ,从水稻未成熟种子cDNA文库中分离到 5个新的MYB基因家族成员 ,它们是OsMYB12、13、14、15和5 1。在酵母系统中证实OsMYB13、OsMYB15和Os MYB5 1蛋白具有转录激活功能。Northern印迹分析表明 ,OsMYB5 1主要在未成熟种子中表达 ,在根和小苗中表达水平较低。RT PCR分析表明 ,OsMYB15在根、茎、小穗、叶片和种子中有低水平的表达     

Genome-wide analysis of genomic imprinting in the endosperm and allelic variation in flax

Genomic imprinting is an epigenetic phenomenon that causes biased expression of maternally and paternally inherited alleles. In flowering plants, genomic imprinting predominantly occurs in the triploid endosperm and plays a vital role in seed development. In this study, we identified 248 candidate imprinted genes including 114 maternally expressed imprinted genes (MEGs) and 134 paternally expressed imprinted genes (PEGs) in flax (Linum usitatissimum L.) endosperm using deep RNA sequencing. These imprinted genes were neither clustered in specific chromosomal regions nor well conserved among flax and other plant species. MEGs tended to be expressed specifically in the endosperm, whereas the expression of PEGs was not tissue-specific. Imprinted single nucleotide polymorphisms differentiated 200 flax cultivars into the oil flax, oil-fiber dual purpose flax and fiber flax subgroups, suggesting that genomic imprinting contributed to intraspecific variation in flax. The nucleotide diversity of imprinted genes in the oil flax subgroup was significantly higher than that in the fiber flax subgroup, indicating that some imprinted genes underwent positive selection during flax domestication from oil flax to fiber flax. Moreover, imprinted genes that underwent positive selection were related to flax functions. Thirteen imprinted genes related to flax seed size and weight were identified using a candidate gene-based association study. Therefore, our study provides information for further exploration of the function and genomic variation of imprinted genes in the flax population.     

种子特异性启动子研究进展

植物的种子,尤其是油料和谷类作物的种子与人类的生产生活关系非常密切,因此,也成为植物基因工程中进行改良的重要目标材料。转化的外源基因在植物受体组织中能否正确、高效并按照人们的意愿特异地表达是人们非常关注的问题。启动子驱使外源基因在受体植株中启动转录是外源基因能够表达的必要条件。目前人们所广泛研究的种子特异性启动子基本上属于II类启动子,它可以驱使外源基因在植物的种子中特异表达,按照人们的意愿改进植物代谢途径,提高种子中营养物质含量等。种子特异性启动子的结构符合II类启动子的特点,具有基本启动子、起始子和上游元件。它区别于其它类型启动子的一个 显著特点是上游存在一些特异的调控元件与调控种子特异性基因的特异表达有关。本文综述了高等植物种子特异性启动子的结构及其在植物基因工程中的最新研究进展。对这类启动子的结构和功能元件的了解,有助于人们更加深入地理解高等植物基因表达调控机制,提高人们对植物种子发育过程及有机物在种子中积累机制的认识,而且可以为植物基因工程中生物反应器的研究提供有应用价值的启动子元件。