Expression,Imprinting, and Evolution of Rice Homologs of the Polycomb Group Genes

Polycomb group proteins （PcG） play important roles in epigenetic regulation of gene expression. Some core PeG proteins, such as Enhancer of Zeste （E（z））, Suppressor of Zeste （12） （Su（z）12）, and Extra Sex Combs （ESC）, are conserved in plants. The rice genome contains two E（z）-Iike genes, OsiEZ1 and OsCLF, two homologs of Su（z）12, OsEMF2a and OsEMF2b, and two ESC-like genes, OsFIE1 and OsFIE2. OsFIE1 is expressed only in endosperm; the maternal copy is expressed while the paternal copy is not active. Other rice PcG genes are expressed in a wide range of tissues and are not imprinted in the endosperm. The two E（z）-Iike genes appear to have duplicated before the separation of the dicots and monocots; the two homologs of Su（z）12 possibly duplicated during the evolution of the Gramineae and the two ESC- like genes are likely to have duplicated in the ancestor of the grasses. No homologs of the Arabidopsis seed-expressed PcG genes MEA and FIS2 were identified in the rice genome. We have isolated T-DNA insertion lines in the rice homologs of three PcG genes. There is no autonomous endosperm development in these T-DNA insertion lines. One line with a T-DNA insertion in OsEMF2b displays pleiotropic phenotypes including altered flowering time and abnormal flower organs, suggesting important roles in rice development for this gene.     

Protein-Repairing Methionine Sulfoxide Reductases in Photosynthetic Organisms： Gene Organization,Reduction Mechanisms,and Physiological Roles

Methionine oxidation to methionine sulfoxide （MetSO） is reversed by two types of methionine sulfoxide reducrases （MSRs）, A and B, specific to the S- and R-diastereomers of MetSO, respectively. MSR genes are found in most organisms from bacteria to human. In the current review, we first compare the organization of the MSR gene families in photosynthetic organisms from cyanobacteria to higher plants. The analysis reveals that MSRs constitute complex families in higher plants, bryophytes, and algae compared to cyanobacteria and all non-photosynthetic organisms. We also perform a classification, based on gene number and structure, position of redox-active cysteines and predicted sub-cellular localization. The various catalytic mechanisms and potential physiological electron donors involved in the regeneration of MSR activity are then de- scribed. Data available from higher plants reveal that MSRs fulfill an essential physiological function during environmental constraints through a role in protein repair and in protection against oxidative damage. Taking into consideration the ex- pression patterns of MSR genes in plants and the known roles of these genes in non-photosynthetic cells, other functions of MSRs are discussed during specific developmental stages and ageing in photosynthetic organisms.     

拟南芥灰霉病抗性相关转录因子

病原菌的侵染激发植物大量防御响应基因的表达, 其中转录因子在协调庞大的抗病防御网络中发挥重要作用。灰葡萄孢菌(Botrytis cinerea)是最具破坏力的死体营养型病原真菌之一, 在农业生产上造成严重的经济损失。文章综述了ERF(Ethylene response factors)、WRKY、MYB等家族中参与灰霉病防御反应的转录因子的功能研究进展。转录因子通过复杂的mRNA或蛋白水平的互作方式构成了精细的调控网络, 以激活下游防卫基因的表达, 从而诱导抗病反应。一部分转录因子是协调不同激素信号通路交叉响应的重要节点和调节器, 将植物抵御不同类型病原菌的分子机制联系起来。对这类转录因子的研究将为研究植物其他病原菌防御机制提供线索, 另外深入理解抗病机制将有助于研究者在作物改良和保护中更高效地利用抗病基因。