Antisense suppression of thioredoxin h mRNA in Brassica napus cv. Westar pistils causes a low level constitutive pollen rejection response Yosr Z. Haffani 1,3 , Thierry Gaude 2 , J. Mark Cock 2,4 and Daphne R. Goring 1, * 1 Department of Botany, University of Toronto, Toronto, Ontario, Canada M5S 3B2; 2 Reproduction et De´veloppement des Plantes, UMR 5667 CNRS-INRA-ENSL-Universite´ de Lyon, IFR 128 BioSciences Lyon- Gerland, E ´ cole Normale Supe´rieure de Lyon, 46 alle´e d’Italie, 69364 Lyon Cedex 07, France; 3 Current address: Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto Ontario, Canada M5G 1X5; 4 Current address: Unite ´ Mixte de Recherche 7139, CNRS-Goemar-Universite ´ Paris 6, Station Biologique, Place Georges Teissier, BP 74, 29682 Roscoff Cedex, France (*author for correspondence; e-mail goring@botany.utoronto.ca) Received 26 May 2004; accepted in revised form 5 July 2004 Key words: pollen–pistil interactions, receptor kinase, self-incompatibility, thioredoxin Abstract In Brassica, the thioredoxin h proteins, THL1 and THL2, were previously found to be potential inhibitors of the S receptor kinase (SRK) in the Brassica self-incompatibilty response. To investigate the biological roles of THL1 and THL2 in pollen–pistil interactions, the stigma-specific SLR1 promoter was used to drive antisense THL1/2 expression in Brassica napus cv. Westar. This cultivar is normally compatible, but antisense suppression of THL1/2 led to a low level constitutive rejection of all Brassica napus pollen tested. Fluorescence microscopy revealed that the pollen rejection was a typical Brassica self-incompatibility rejection response with reduced pollen adhesion, germination and pollen tube growth. In addition, Westar was found to express the SLG 15 and SRK 15 proteins which may be the target of regulation by THL1 and THL2. Thus, these results indicate that the THL1 and THL2 are required for full pollen acceptance in B. napus cv. Westar. Abbreviations: ARC1, arm repeat containing-1; KAPP, kinase associated protein phosphatase; MLPK, M locus protein kinase; SCR, S locus cysteine-rich protein; SLG, S locus glycoprotein; SLR, S locus related; SP11, S locus protein 11; SRK, S receptor kinase; THL, thioredoxin-like Introduction In Brassica, the initial stages of pollination involve cell–cell interactions between pollen and stigmatic papillae at the surface of the pistil which can then lead to the acceptance or rejection of the pollen. Typically, when a compatible pollen grain lands on the stigmatic surface, the surrounding pollen coat flows to the area of contact between the pollen grain and the stigmatic papilla to facilitate pollen adhesion, hydration, and germination. The outer surface of the pollen plays a critical role in this initial adhesion event as well as the subsequent expansion of the stigmatic papilla cell wall in the contact region (reviewed in Dickinson, 1995; Wheeler et al., 2001). On the stigmatic side, the S locus-related (SLR)-1 protein has also been found to be required for pollen adhesion (Luu et al., 1999). Following adhesion and germination, the emerging pollen tube penetrates the expanded cell Plant Molecular Biology 55: 619–630, 2004. Ó 2004 Kluwer Academic Publishers. Printed in the Netherlands. 619