【作者】 赵素珍；

【导师】 种康； 孟征；

【作者基本信息】 中国科学院研究生院（植物研究所） ， 植物学， 2005， 博士

【摘要】 MADS-box基因是一个大的转录因子家族,在花发育过程中起重要作用。根据对双子叶模式植物拟南芥、金鱼草和矮牵牛遗传突变体的研究,提出了花发育的ABCDE模型。该模型认为:A、B、C、D、E代表了5类功能不同的花器官特征基因,单独或联合控制花器官的发育。在这5类基因中,E类基因的功能较为复杂,它不仅是花器官特征基因,而且具有花分生组织决定性(Floral meristem determinency)。在单子叶植物中,E类基因的功能发生了很大的分化。水稻是单子叶植物的模式植物,水稻中至少有5个E类基因,分别是OsMADS1、OsMADS5、OsMADS7、OsMADS8和OsMADS34 ,其中除了对OsMADS1基因有较深入的研究外,对其它几个E类基因的功能了解甚少。我们以OsMADS8基因为切入点,利用组织原位杂交,RNAi技术对水稻中的E类基因进行了深入的研究。结果表明:OsMADS8/7基因早在花序枝梗分生组织原基就有转录,随着小穗的生长发育,逐渐集中在小穗分生组织原基,小花分生组织原基,浆片、雄蕊和心皮中表达; 在胚珠形成时,内外珠被有很强的杂交信号,而且在幼胚和胚乳中也有表达。OsMADS5在幼花时期,四轮花器官均有表达,在小穗发育后期及受精后的表达方式与OsMADS8/7基因相同。OsMADS8基因被抑制后,转基因植株没有任何表型变化,说明很可能有其它E类基因弥补了OsMADS8基因的功能缺失; 当同时抑制其它E类基因的表达时,转基因植株抽穗期明显延长,四轮花器官的发育均受到影响:稃片类似叶片状; 浆片转变为稃片类的结构; 雄蕊没有花粉; 心皮具有了稃片的特点; 没有胚珠结构的形成,同时失去了花分生组织决定性,在心皮的部位产生了新的花器官或花分生组织逆转为花序分生组织。说明水稻四轮花器官及胚珠的正常发育需要E类基因的参与,但其功能与双子叶植物如拟南芥,矮牵牛等直系同源基因相比已经发生变化; 水稻中的E类基因在维持花分生组织特征性方面起重要作用; 另外对抽穗期有影响。研究MADS-box基因的调控序列可以进一步揭示影响基因时空表达的内外因素。ZAG2是玉米MADS-box基因中的D类基因,控制胚珠的发育,在胚珠和心皮的内表面特异表达。我们从玉米基因组分离到了ZAG2基因翻译起始点上游3040bp的序列,并利用5’-RACE方法鉴定出了转录起始点的位置。通过不同更多还原

【Abstract】 MADS-box genes encode a family of transcriptional factors that play a key role in flower development. Studies on several floral homeotic mutants in dicots, mainly in Arabidopsis, Snapdragan and Petunia, established the ABCDE model for the determination of floral organ identities. Class E genes contribute to the development of petals, stamens and carpels, in addition to sepals. It also specifies the floral meristem identity. In grasses, E-function genes underwent a relatively rapid functional diversification. There are at least five class E genes in rice. They are OsMADS1, OsMADS5, OsMADS7 (OsMADS45), OsMADS8 (OsMADS24) and OsMADS34, in which OsMADS1 is currently the best characterized, the others are not documented well. On the basis of the results from dicots, we investigated the E function genes in rice using In Situ Hybridization and RNAi technique. The results showed that OsMADS8/7 transcripts are first detected in branching primordia, then in spikelet meristem primordia. With the development of the flower, OsMADS8 transcripts are localized in the lodicules, developing stamens and pistil. OsMADS8 continues to express in integuments, developing embryo and endersperm. OsMADS5 has similar expression patterns to OsMADS8/7. The difference is that OsMADS5 transcripts present in all floral whorls at early stage of the flower development. Silencing of OsMADS8 by RNAi strategy had no phenotypic alteration when compared to wild-type plants, but if all the E function genes were silenced in the mean time, the floral organs and heading date were seriously affected. The palea and lemma were transformed into leaf-like structures; the lodicules were palea-like and the stamens did not produce pollen. The carpels had characteristics of palea/lemma. Ovule was not formed in the aberrant carpel and floral reversion occurred. It suggested that there is functional redundancy among class E genes in rice, in addition to the diversification; class E genes are required for the development of all four floral organs and ovule; E function genes specify the floral meristem identity and affected the heading date of rice. Studies on the regulatory sequence of MADS-box genes will reveal spatial and temporal control of gene expression. ZAG2 gene belongs to the class D gene of MADS-box genes in maize. It expresses in ovules and carpels. We isolated the sequence of 3040bp upstream of the translational start site of the gene. The transcriptional start site in the sequence was identified by the method of 5’-RACE. Two gene fusions between the ZAG2 genomic region and the GUS reporter gene were assembled and introduced into rice. We analyzed the regulatory sequence according to the primary results.更多还原