Cloning and characterization of 5 MADS-box cDNAs isolated from citrus fruit tissue

We isolated and characterized 5 MADS-box cDNA clones of CitMADS1, CitMADS3, CitMADS5, CitMADS6 and CitMADS8 from fruit tissues of Satsuma mandarin (Citrus unshiu Marc.). Sequence analysis revealed that they have high sequence identities with known MADS-box genes and that their predicted proteins possess the general structural features of the M domain and the K domain. In a phylogenetic tree with 24 known Arabidopsis MADS-box genes, 5 Citrus MADS-box genes were classified into 4 clades of the MADS-box gene with independent gene functions. Their broad expression profiles in the Citrus life cycle suggested that they play roles in flower and fruit development. Most of them, except CitMADS1 and CitMADS3, are expressed in seedlings before the phase transition from vegetative to reproductive growth. CitMADS1 and CitMADS3 are not expressed in vegetative organs and could serve as a molecular marker for reproductive development.