Abstract: A MADS-box gene，named CiMADS9，was isolated from the male flowers of Carya illinoinensis using the gene specific primers obtained according to a MADS conserved fragment sequence by the method of RACE technology. The gene was 1 077 bp which has an ORF of 768 bp coding 255 amino acids．Multiple sequence comparison revealed that CiMADS9 was the typical MIKC-type MADS-box genes with the MADS-box domain and K semi-conservative region. Phylogenetic analysis indicated that CiMADS9 belonged to the AGL15 group of MADS-box gene family. qRT-PCR indicated that the expression level of reproductive organs（male flower，female flower，and young fruit）were striking higher than those of vegetative organs（leaf and branch），and the expression level of male flower was the highest among all the organs. The overexpression vector of CiMADS9 was constructed and transferred into Arabidopsis thaliana，and then resistant plants were obtained. RT-PCR analysis showed that CiMADS9were expressed in all these lines. Compared with the wide type，transgenic Arabidopsis thaliana overexpressing CiMADS9 gene delayed flowering time and increased the number of leaf.

Key words: Carya illinoinensis, flower organ development, CiMADS9, gene expression, function analysis