Poster: Integrated Plant Biology

Abs # 87: Essential roles for PPR proteins in plant embryogenesis revealed by Arabidopsis emb-PPR knock-out mutants

Presenter:	Vernon, Daniel M
Authors	Vernon, Daniel M (A)   Cushing, Daniel A (A)   Houghland, John E. (A)   Gestaut, Daniel R (A)
Affiliations:	(A): Whitman College

Pentatricopeptide Repeat (PPR) proteins are present in diverse eukaryotes. Some are known to function in organelle RNA processing and translational regulation. The PPR superfamily has undergone explosive evolution in plants and is one of the largest plant protein families: more than 200 PPR genes have been identified in the Arabidopsis genome. Previously, we reported that the Arabidopsis embryo-defective175 locus encodes a PPR protein- the first to be implicated in plant development. Here we describe additional embryo-defective PPR mutants. We searched publicly available emb mutant collections for T-DNA-tagged PPR genes, and identified 7 additional loci with prospective roles in development. All of the mutant alleles contained inserts within coding regions, 5' UTRs, or proximal promoter regions. We investigated the structures of these genes using available EST & cDNA sequences. Interestingly, 3 of the 8 EMB-PPR genes are unusually close to adjacent genes and had been incorrectly annotated with those genes as chimeric transcription units. RT-PCR indicated that the EMB-PPRs are all transcribed in leaves, roots, flowers, and developing seeds. As a group they encode diverse proteins containing from 9 to 24 PPR motifs. All are predicted to localize to chloroplasts or mitochondria. Nomarski DIC microscopy of mutant embryos revealed diverse defects, ranging from consistent arrest at the globular stage in some lines to variable arrest and defects in late-stage embryo morphology, such as enlarged shoot meristems and stunted cotyledons, in others. These emb-PPR mutants provide evidence that multiple members of this large protein family have diverse & essential roles in early plant development. Supported by the Murdock Charitable Trust