Characterization and functional analysis of MADS-box genes in the vegetative and reproductive development of Populus tremuloides

The MADS-box proteins in plants are the 'molecular directors' of plant development. They have a conserved DNA-binding domain called MADS domain. The regions outside the MADS domain, i.e., the K and I regions, mediate the functional specificity by interacting with other protein molecules and participating in gene regulation as protein complexes. Interaction of MADS-box proteins with members of their own class or other cellular proteins at the molecular level may explain the differentiation of meristem to vascular and floral tissues in aspen. Populus tremuloides with a long juvenile period is a tree species that is both ecologically and economically very important. Poplar species including P. tremuloides have a two whorl floral structure unlike the typical four-whorl structure seen in Arabidopsis. Studying floral specific genes like PTM1/2/3/4/6/7 and 8 will lead to a better understanding of what makes poplar flowers form a two-whorl flower. Yeast two-hybrid screening showed that PTM5, a vegetative tissue specific MADS-box protein interacts with actin depolymerizing factor (ADF) and leucine rich repeat (LRR) proteins. PTM5 and ADF show similar gene expression patterns and their expressions in the root lead to the hypothesis that their manipulation may result in increased root biomass. The modulation of the expression of MADS-box genes like PTM5, isolated from aspen trees and their interacting partners, like ADF and LRR will be a useful tool to manipulate vegetative tissue development in trees. Floral genes show differential expression in the two floral whorls of aspen. PTM1 and 2 are expressed in the outer perianth cup where the expression of other floral genes like PTM3/4 and 6, which are expressed in the inner reproductive whorl are absent. The modulation of floral identity genes can be used to manipulate flower development and produce sterile transgenic lines that will prevent the contamination of the natural plant community with transgenic genes.