Originally published as Genetics Published Articles Ahead of Print on August 24, 2008.

Genetics, Vol. 180, 229-236, September 2008, Copyright © 2008
doi:10.1534/genetics.108.091736

UBIQUITIN-SPECIFIC PROTEASE 26 Is Required for Seed Development and the Repression of PHERES1 in Arabidopsis

Ming Luo*,1,2, Ming-Zhu Luo{dagger},1, Diana Buzas*, Jean Finnegan*, Chris Helliwell*, Elizabeth S. Dennis*, W. J. Peacock* and Abed Chaudhury*,3

* CSIRO Plant Industry, Canberra, ACT 2601, Australia and {dagger} College of Agronomy, South China Agricultural University, Guangzhou 510624, China

2 Corresponding author: CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2601, Australia.
E-mail: ming.luo{at}csiro.au

The Arabidopsis mutant Atubp26 initiates autonomous endosperm at a frequency of ~1% in the absence of fertilization and develops arrested seeds at a frequency of ~65% when self-pollinated. These phenotypes are similar to those of the FERTILIZATION INDEPENDENT SEED (FIS) class mutants, mea, fis2, fie, and Atmsi1, which also show development of the central cell into endosperm in the absence of fertilization and arrest of the embryo following fertilization. Atubp26 results from a T-DNA insertion in the UBIQUITIN-SPECIFIC PROTEASE gene AtUBP26, which catalyzes deubiquitination of histone H2B and is required for heterochromatin silencing. The paternal copy of AtUBP26 is able to complement the loss of function of the maternal copy in postfertilization seed development. This contrasts to the fis class mutants where the paternal FIS copy does not rescue aborted seeds. As in the fis class mutants, the Polycomb group (PcG) complex target gene PHERES1 (PHE1) is expressed at higher levels in Atubp26 ovules than in wild type; there is a lower level of H3K27me3 at the PHE1 locus. The phenotypes suggest that AtUBP26 is required for normal seed development and the repression of PHE1.