Journal of Integrative Plant Biology 2013, 55 (8): 682–695 Research Article PHOSPHATIDYLSERINE SYNTHASE1 is Required for Inflorescence Meristem and Organ Development in Arabidopsis F Chengwu Liu 1 , Hengfu Yin 1 , Peng Gao 1 , Xiaohe Hu 2 , Jun Yang 1 , Zhongchi Liu 3 , Xiangdong Fu 4 and Da Luo 1,2 * 1 National Key Laboratory of Plant Molecular Genetics, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, the Chinese Academy of Sciences, Shanghai 200032, China 2 State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou 510275, China 3 Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742, USA 4 State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, the Chinese Academy of Sciences, Beijing 100101, China ∗ Corresponding author Fax : +86 20 3994 3513; E-mail: dluo@sibs.ac.cn F Articles can be viewed online without a subscription. Available online on 11 March 2013 at www.jipb.net and www.wileyonlinelibrary.com/journal/jipb doi: 10.1111/jipb.12045 Abstract Phosphatidylserine (PS), a quantitatively minor membrane phospholipid, is involved in many biological processes besides its role in membrane structure. One PS synthesis gene, PHOSPHATIDYLSERINE SYNTHASE1 (PSS1), has been discovered to be required for microspore development in Arabidopsis thaliana L. but how PSS1 affects postembryonic development is still largely unknown. Here, we show that PSS1 is also required for inflorescence meristem and organ development in Arabidopsis. Disruption of PSS1 causes severe dwarfism, smaller lateral organs and reduced size of inflorescence meristem. Morphological and molecular studies suggest that both cell division and cell elongation are affected in the pss1-1 mutant. RNA in situ hybridization and promoter GUS analysis show that expression of both WUSCHEL (WUS) and CLAVATA3 (CLV3) depend on PSS1. Moreover, the defect in meristem maintenance is recovered and the expression of WUS and CLV3 are restored in the pss1-1 clv1-1 double mutant. Both SHOOTSTEMLESS (STM) and BREVIPEDICELLUS (BP) are upregulated, and auxin distribution is disrupted in rosette leaves of pss1-1. However, expression of BP, which is also a regulator of internode development, is lost in the pss1-1 inflorescence stem. Our data suggest that PSS1 plays essential roles in inflorescence meristem maintenance through the WUS-CLV pathway, and in leaf and internode development by differentially regulating the class I KNOX genes. Keywords: Arabidopsis; CLV3; KNOX; WUS; meristem. Liu C, Yin H, Gao P, Hu X, Yang J, Liu Z, Fu X, Luo D (2012) PHOSPHATIDYLSERINE SYNTHASE1 is required for inflorescence meristem and organ development in Arabidopsis. J. Integr. Plant Biol. 55(8), 682–695. Introduction Plants produce aerial organs continuously from stem cells in the shoot apical meristem (SAM) throughout their lives. In Ara- bidopsis, stem cell activity is regulated by the WUS-CLV nega- tive feedback loop in which WUS induces CLV3 expression in stem cells and the CLV complex restricts WUS expression in the organization center (OC) (Brand et al. 2000; Schoof et al. 2000). Thes components in this signaling pathway include stem cell identity gene WUS (Laux et al. 1996; Mayer et al. 1998), a ligand protein encoded gene CLV3 (Fletcher et al. 1999; Kondo et al. 2006; Ohyama et al. 2009), and three major receptor systems, CLV1 (Clark et al. 1997), CLAVATA2 (CLV2) – CORYNE (CRN) (M¨ uller et al. 2008; Bleckmann et al. 2010; C  2013 Institute of Botany, Chinese Academy of Sciences