Phosphatidylserine synthase 1 is required for inflorescence meristem and organ development in Arabidopsis

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.