棉花MADS框基因GhMADS3的克隆及其组成型表达对烟草花器官决定的影响

MADS框基因在植物花器官发育中发挥着关键性作用。为研究棉花花器官发育的机理,以徐州142花蕾为材料,利用EST数据库资料,通过EST序列整合,克隆出了一个MADS域蛋白的编码区段,GenBank登录号为AY083173。该片段(GhMADS3)包含一个732 bp的开放阅读框,推导的氨基酸序列(244氨基酸)与可可,黄瓜,烟草,矮牵牛,金鱼草等的AG亚家族基因的序列相似性高。进化树重建分析将GhMADS3基因归入MADS框基因AG亚家族C功能分支的euAG分支。RT-PCR分析显示,该基因在雄蕊和心皮中表达,在根、茎、叶等营养器官,萼片,花瓣,花器官变异体chv1(所有花器官均变为苞叶状器官)的花蕾中不表达。将GhMADS3与35S启动子融合构建成嵌合基因转化烟草,转基因烟草植株花朵出现萼片(轮1)向心皮,花瓣(轮2)向雄蕊的转变,花器官表现明显的白化倾向。同时,在轮1观察到丝状结构的出现,该结构在此前类似的研究中尚无报道。这些结果说明,实验中克隆了一个有生物学功能的棉花的AG亚家族MADS框基因,该基因可能在棉花花器官发育中有重要的功能。

Cloning of a MADS Box Gene (GhMADS3) from Cotton and Analysis of Its Homeotic Role in Transgenic Tobacco

A MADS box gene(GhMADS3)was cloned from cotton(Gossypium hirsutum L.)based on EST sequences.The pre- dicted protein sequence of GhMADS3 showed 85%,73%,and 62%identity with Theobroma cacao TcAG,Antirrhinum majus FAR, and Arabidopsis thaliana AG,respectively,and was grouped with AG homologues when the full length sequences excluding N-extensions were compared.GhMADS3 expressed in the wild type cotton flower primarily in stamens and carpels,which was comparable to AG in Arabidopsis.However,it was not expressed in floral buds of a homeotic cotton variant chv1.Ectopic expres- sion of GhMADS3 in tobacco(Nicotiana tabacum L.)resulted in flowers with sepal-to-carpel and petal-to-stamen transformation. The carpelloid first whorl organs,with stigmatic tissue on their upper edges,had a white appearance when compared with the dark green color of the wild type sepals.At times,long filaments were observed at the fusion site of the first carpelloid oranges.The second whorl organs in staminoid were usually smaller than the wild type and the color was changed from pink to white.These results suggest that GhMADS3 has a homeotic role in flower development.