Minisymposium 23: Protein targeting

Abs # 44002: Developmentally regulated nuclear-envelope association in plants: the Arabidopsis MAF protein family

Presenter:	Patel, Shalaka , patel.492@osu.edu
Authors	Patel, Shalaka  (A)   Rose, Annkatrin  (A)   Meulia, Tea  (B)   Meier, Iris  (A)
Affiliations:	(A): Plant Biotechnology Center and Department of Plant Biology, 244 Rightmire Hall, 1060 Carmack Road, Ohio State University, Columbus, OH 43210 (B): Molecular and Cellular Imaging Center, Ohio State University/OARDC, 1680 Madison Ave. Wooster OH 44691

The nuclear envelope (NE) separates chromatin from the cytoplasm and is involved in organizing nuclear architecture. It also provides an anchoring surface for chromatin and plays a role in the complex dissociation and re-association of the nucleus during open mitosis. While well-researched in vertebrates, the protein composition of the NE in plants is barely understood. MAF1 is a 16 kD, NE-associated protein first identified in tomato. MAF1-like proteins are widely conserved in land plants, but no homologs are found outside the plant kingdom, consistent with a plant-specific role at the NE. Three MAF1-like proteins are encoded in the Arabidopsis genome, AtMAF1, AtMAF2 and AtMLP. AtMAF1-GFP and AtMAF2-GFP, but not AtMLP-GFP fusion proteins are targeted to the NE in transiently transformed Arabidopsis protoplasts. A core domain that is necessary and sufficient for NE targeting was mapped in AtMAF1. A point mutation that changes a conserved tryptophan-proline motif in the conserved core domain of the protein disrupts NE targeting. Transgenic Arabidopsis plants expressing AtMAF1-GFP and AtMAF2-GFP under the control of the 35S promoter show a tissue-specific sub-cellular localization pattern. Both fusion proteins are associated with the NE in undifferentiated root tip cells. In differentiated cells (mature root, leaf epidermal and hypocotyl cells), the fusion proteins are diffusely located in the nucleus and the cytoplasm. In callus induced from differentiated root segments, the fusion proteins are associated with the NE. Cumulative evidence from the above data suggests that AtMAF1 and AtMAF2 are targeted to the NE in a developmentally regulated fashion. Preliminary immunogold labeling data indicate that in callus cells AtMAF1-GFP is associated with the outer NE. RNAi lines with undetectable expression of all three genes at the RNA as well as protein level have shorter primary roots and a reduced number of lateral roots. No change is seen in cell size or number in the root elongation zone. These observations lead to the hypothesis that MAF knockdown affects the rate of cell division in root meristems. Analysis of the mitotic activity of root meristems in the RNAi lines is in progress. Together, these data indicate that AtMAF1 and AtMAF2 are involved in a NE function in undifferentiated plant cells and provide the first example for regulated NE targeting of a plant protein.