Objective  To provide data in molecular-level for revealing the regulatory role of MlCYP734A6 in the growth and development of Musella lasiocarpa.

Method  The 3′ and 5′ RACE technology was used to clone the full length cDNA of MlCYP734A6 gene. The software of bioinformatics was used to analyze the nucleotides and protein sequence. Real-time PCR method was used to analyze the gene expression level in different types and tissues of Musella lasiocarpa. HPLC-MS/MS was used to detect the brassinolide content in different tissues.

Result  The full length cDNA of MlCYP734A6 is 1 584 bp, encoding 527 amino acids. The relative molecular mass of coding protein is 60 038.84 Da and the isoelectric point is 6.61. Sequence comparison and phylogenetic tree analysis showed that the amino acid sequence of MlCYP734A6 had the closest evolutionary relationship with the CYP734A6 protein of Musa acuminata subsp. malaccensis. Real-time PCR analysis showed that MlCYP734A6 could be detected in all tissues. The two tissues with the highest expression level were rachis and root tip, and the lowest expression level was in leaf. No significant correlation was found between the brassinolide content and the expression pattern of MlCYP734A6, and excessive brassinosteroids in RD05 was a possible cause of dwarfed phenotype.

Conclusion  The study indicated that MlCYP734A6 may participate in the metabolism of brassinosteroids, and balance the bioactive brassinosteroids content in Musella lasiocarpa. These results provide further theoretical support for the role of CYP734As in plant growth and development in the future.