Abstract: Based on EST sequence data analysis，PMADS20（GU129907）was cloned from Petunia
hybrid by PCR using inflorence cDNA as template. Phylogenetic analysis shows that PMADS20 belongs to
SVP clade of StMADS11 subfamily and is most closely related to tomato and pepper JOINTLESS.
qRT-PCR analysis indicated that PMADS20 mRNA accumulated high level in vegetative organs，and low
level in flowers. Vectors of over-expressing PMADS20 and PMADS20-SRDX were constructed. When they
were introduced into petunia using Agrobacterium-mediated transformation method，both 35S︰PMADS20
and 35S︰PMADS20-SRDX transgenic floral organs exhibited leaf-like characteristics. However，the
alterations of 35S︰PMADS20-SRDX flowers were more severe than that of the 35S︰PMADS20 flowers. The 35S︰PMADS20-SRDX petals and pistils showed the unshaven floral phenotype which
characterized by ectopic trichome and stoma formation on adaxial side of petals and the surface of ovaries
and styles. The results suggest that PMADS20 functions in flower development by transcriptional
suppression. Constitutive expression of PMADS20 did not lead to obvious changes in plant stature，while
the internodes of 35S︰PMADS20-SRDX transgenic inflorences were shorter than that of the wild type.
These results suggest that PMADS20 may function differently between in petunia inflorence internode and
flower development.

Key words: petunia, StMADS11 subfamily, PMADS20, floral organ development