矮化香蕉及其野生型GA3ox基因的结构特点和表达分析

香蕉的矮化突变是香蕉无性繁殖后代最常见的表型变异之一,但其变异的分子调控机理目前尚未研究清楚; 而内源赤霉素是影响植物株高的重要激素之一,GA3-氧化酶是赤霉素生物合成后期的关键酶。为探究GA3-氧化酶编码基因对香蕉矮化的分子调控机理,该研究以威廉斯B6矮化突变体及其野生型亲本为材料,通过RT-PCR技术克隆得到矮化香蕉及其野生型亲本GA3ox基因的全长cDNA序列,并对其推测的氨基酸序列进行比对分析,同时利用qRT-PCR技术对GA3ox基因在不同组织中的表达水平差异进行分析。结果表明:(1)矮化香蕉GA3ox-A和野生型香蕉GA3ox-G的ORF长度均为864 bp,均编码287个氨基酸,经序列比对分析发现两条氨基酸序列之间存在5个位点的差异,从而产生具有不同性质的蛋白质。(2)氨基酸序列同源性分析表明,矮化香蕉GA3ox的氨基酸序列与油棕、海枣、椰子的同源性最高。(3)qRT-PCR显示,GA3ox基因在矮化香蕉叶片和茎秆中的表达水平整体上低于野生型,其中GA3ox在野生型茎秆中的表达水平是矮化植株的2.2～32倍。综上推测,GA3ox基因可能对香蕉茎杆的矮化变异具有重要的调控作用。该研究结果为揭示香蕉矮化突变的分子机制与筛选优良矮化香蕉株系奠定了基础。

Structural characteristics and expression analysis of GA3ox gene in dwarf and wild type bananas

Dwarf mutation is one of the most common phenotypic variations in bananas reproduce asexually, but its variation regulation mechanism has not been studied clearly. Endogenous gibberellin is one of the important hormones affecting plant height, and GA3-oxidase is the key enzyme in the late biosynthesis of gibberellin. In order to investigate the molecular regulation mechanism of GA3-oxidase encoding gene on banana dwarfing, the full-length cDNA sequences of GA3ox gene from Williams B6 dwarfing mutant and its wild type parent were cloned by RT-PCR, and their presumed amino acid sequence were compared and analyzed. Meanwhile, the expression level of the GA3ox gene in different tissues of dwarf banana and its wild type were analyzed by qRT-PCR. The results were as follows:(1)The ORF lengths of the dwarf banana GA3ox-A and the wild type GA3ox-G were both 864 bp, and are all encoded with 287 amino acids. The comparison of the two amino acid sequences showed that there were five differences, which resulted in proteins with different properties.(2)Amino acid sequence homology analysis showed that the amino acid sequences of dwarf banana GA3ox had the highest homology with oil palm, date palm and coconut.(3)The qRT-PCR showed that the expression levels of GA3ox in dwarf banana leaves and stems were lower than those of wild type. The expression level of GA3ox in wild type stems was 2.2 to 32 times as high as that in dwarf plants. Therefore, these results illustrate that GA3ox gene may play an important role in regulating the dwarfing variation of banana stem.