SUMO PROTEASE RELATED TO FERTILITY 1 and -2, the SUMO proteases, are required for fertility in Arabidopsis
Linpo Liu^{1, 2, §}, Ying Jiang^{1, 2, §}, Xiaomei Zhang¹, Xu Wang¹, Yuzhen Han², George Coupland³, Yong-Fu Fu^{1, *}

¹MOA Key Lab of Soybean Biology (Beijing), Institute of Crop Sciences, The National Key Facility for Crop Gene Resources and Genetic Improvement, Chinese Academy of Agricultural Sciences, Nandajie 12, Zhongguancun, Haidian District, Beijing 100081, P. R. China
²College of Biological Sciences, State Key Laboratory of Plant Physiology and Biochemistry, China Agricultural University, No. 2 Yuanmingyuan Xilu, Haidian District, Beijing, 100094, P. R. China
³Max Planck Institute for Plant Breeding, Carl-von-Linne Weg 10, D-50829 Cologne, Germany
^§These authors contribute equally.
^* Corresponding author. E-mail fuyf@caas.net.cn; Tel/Fax +86-10-82105864

Abstract
Sumoylation is involved in extensive cellular processes in Eukaryotes. In planta, SUMO is implicated in flowering-time control, responses to biotic and abiotic stress. Here, we report that two proteins, SUMO PROTEASE RELATED TO FERTILITY (SPF) 1 and 2, regulate a number of aspects of reproductive fertility in Arabidopsis thaliana. The single spf1 mutant exhibits some abnormalities in flower structure and embryos, but the pollen and ovules are morphologically normal, while the single spf2 mutant is largely wild type. However, spf2 enhances the phenotype of spf1 mutants so that the spf1 spf2 double mutant exhibits more serious abnormalities in micro- and mega-gametophytes and embryos. The data of both RT-PCR and promoter GUS fusions shows that expression of these two genes is largely confined to reproductive tissues. SPF1 and SPF2 can interact with different SUMO isoforms in yeast. SPF1 protein displays in vitro a SUMO protease activity, and the pattern of SUMO-conjugate accumulation in the inflorescences, but not in seedlings, of the spf1 spf2 mutant differs from that of the wild type. Our results indicate that SPF1 and SPF2 are SUMO proteases active in reproductive tissues of Arabidopsis and contribute to fertility.

Key words: SUMO, fertility, gametophytes, embryogenesis, Arabidopsis, embryogenesis