Alvarez-Buylla Elena R, García-Ponce Berenice, Garay-Arroyo Adriana
Laboratorio de Genética Molecular, Desarrollo y Evolución de Plantas, Departamento de Ecología Funcional, Instituto de Ecología, UNAM, Ap. Postal 70-275, México DF 04510, México.
J Exp Bot. 2006;57(12):3099-107. doi: 10.1093/jxb/erl081. Epub 2006 Aug 7.
APETALA1 (AP1) and CAULIFLOWER (CAL) are closely related MADS box genes that are partially redundant during Arabidopsis thaliana floral meristem determination. AP1 is able to fully substitute for CAL functions, but not vice versa, and AP1 has unique sepal and petal identity specification functions. In this study, the unique and redundant functions of these two genes has been mapped to the four protein domains that characterize type-II MADS-domain proteins by expressing all 15 chimeric combinations of AP1 and CAL cDNA regions under control of the AP1 promoter in ap1-1 loss-of-function plants. The "in vivo" function of these chimeric genes was analysed in Arabidopsis plants by expressing the chimeras. Rescue of flower meristem and sepal/petal identities was scored in single and multiple insert homozygous transgenic lines. Using these chimeric lines, it was found that distinct residues of the AP1 K domain not shared by the same CAL domain are necessary and sufficient for complete recovery of floral meristem identity, in the context of the CAL protein sequence, while both AP1 COOH and K domains are indispensable for complete rescue of sepal identity. By contrast, either one of these two AP1 domains is necessary and sufficient for complete petal identity recovery. It was also found that there were positive and negative synergies among protein domains and their combinations, and that multiple-insert lines showed relatively better rescue than equivalent single-insert lines. Finally, several lines had flowers with extra sepals and petals suggesting that chimeric proteins yield abnormal transcriptional complexes that may alter the expression or regulation of genes that control floral organ number under normal conditions.
APETALA1（AP1）和CAULIFLOWER（CAL）是密切相关的MADS盒基因，在拟南芥花分生组织决定过程中存在部分冗余。AP1能够完全替代CAL的功能，但反之则不然，并且AP1具有独特的萼片和花瓣身份指定功能。在本研究中，通过在ap1 - 1功能缺失植物中，在AP1启动子的控制下表达AP1和CAL cDNA区域的所有15种嵌合组合，将这两个基因的独特和冗余功能定位到了表征II型MADS结构域蛋白的四个蛋白质结构域上。通过表达这些嵌合体，在拟南芥植物中分析了这些嵌合基因的“体内”功能。在单插入和多插入纯合转基因系中对花分生组织和萼片/花瓣身份的恢复情况进行了评分。利用这些嵌合系发现，在CAL蛋白序列的背景下，AP1 K结构域中与CAL结构域不共有的不同残基对于完全恢复花分生组织身份是必要且充分的，而AP1的COOH和K结构域对于完全恢复萼片身份都是不可或缺的。相比之下，这两个AP1结构域中的任何一个对于完全恢复花瓣身份都是必要且充分的。还发现蛋白质结构域及其组合之间存在正负协同作用，并且多插入系比等效的单插入系表现出相对更好的恢复效果。最后，几个株系的花有额外的萼片和花瓣，这表明嵌合蛋白产生了异常的转录复合物，可能会改变正常条件下控制花器官数量的基因的表达或调控。
