MawuAGL6_1与MawuAGL6_2基因参与调控红花玉兰花被发育的分子机制

Magnolia wufengensis, only found in southwestern Hubei Province, China, belonging to the family Magnoliaceae, an early-diverging clade from ancestral angiosperms. The flowers of M. wufengensis have multiple morphologically identical petaloid tepals instead of distinct sepals and petals, which exhibits a considerable difference from Arabidopsis and other core eudicots. The extreme variation of flower morphologies and the wealth of floral mutants available, has made it an excellent model for discovering the floral development and evolution. Our study revealed that MawuAGL6_1 and MawuAGL6_2 worked together to specifying tepals identity in M. wufengensis. Both genes are AGL6 homologs and encode MADS-box transcription factors. Moreover, Functional analyses displayed that obviously functional divergence within MawuAGL6_1 and MawuAGL6_2. During flower development, MawuAGL6_1 is involved only in the development of petaloid tepals in M. wufengensis. However, ectopic expression of MawuAGL6_2 rescued sepal development in an Arabidopsis ap1 mutant, and produced 1 to 2 extra flowers instead of petals. In combination of various methods and techniques, the proposal aims to document how the MawuAGL6_1 and MawuAGL6_2 gene work together to specify tepal differentiation in M. wufengensis, and uncover the difference of upstream genes regulating the transcription of the both genes. The molecular mechanisms involving in tepal development of these genes working together with other floral organ identity genes are also discussed. These results should provide valuable information to understand the flower evolution in the family Magnoliaceae. Moreover, it should also provide candidate genes for genetic improvement in ornamental tree.

红花玉兰（Magnolia wufengensis ）是木兰科（Magnoliaceae）木兰属（Magnolia）少数具多瓣性状的原始种，仅湖北五峰有野生分布。项目组研究红花玉兰花型调控发现：MawuAGL6_1和MawuAGL6_2是红花玉兰AGL6同源基因，功能分析表明，MawuAGL6_1仅参与调控红花玉兰花被发育；而异位表达的MawuAGL6_2 使拟南芥ap1突变体花萼恢复的同时，还参与花器官数量调控。本项目拟从分析二者转录调控差异入手，系统研究MawuAGL6_1与MawuAGL6_2基因在红花玉兰花被发育调控中的功能，及其协同其他花器官特征决定基因调控不同瓣数红花玉兰花被发育的分子网络。解析MawuAGL6_1和MawuAGL6_2基因参与调控红化玉兰花被发育的分子机制。为探索木兰属植物的起源与花型演化积累资料，并对木兰科观赏花木的花型改良与种质创新提供新的基因资源。

MADS-box基因家族在开花植物的生长和发育调控中起着关键作用。AGL6-like基因具有高度多变的表达模式和多样性的功能，因此该家族一直被认为是MADS-box家族中最神秘的亚族之一，同时其表达模式和功能的多样性长期困扰着研究人员。尽管大量的AGL6同源基因已经从裸子植物和被子植物中分离出来，但其中只有很少部分基因被解析，尤其是对于基部被子植物类群。红花玉兰属于基部被子植物木兰科的一种典型代表，在被子植物的系统衍化历程中占据着极为重要的地位。本项目对红花玉兰AGL6同源基因MawuAGL6-1和MawuAGL6-2在系统发育、表达模式、功能作用以及蛋白-蛋白互作的模式等方面进行了系统研究。系统发育分析结果表明这两个AGL6基因副本可能源于木兰科和樟科分离之前的基因复制事件，并伴随着它们的表达和蛋白-蛋白互作模式的分化差异。功能分析结果表明这两个基因除了具有促进开花的共同功能之外，MawuAGL6-1基因可能单独对花原基决定具有重要作用，而MawuAGL6-2基因可能更倾向于调控花被片的形态建成。本研究解析了红花玉兰MawuAGL6-1和MawuAGL6-2基因的系统进化、组织表达模式和发育调控表达模式、蛋白互作模式和功能，以及对多瓣红花玉兰形成的调控模式。另外，本研究进一步加深了我们对基部被子植物乃至整个AGL6家族基因的系统发育、表达、蛋白间相互作用、功能和AGL6家系基因在进化和生物多样性的重要意义的了解。