Identification of the Pollen Self-incompatibility Determinant in Papaver rhoeas.

Wheeler, Mike, de Graaf, B., Hadjiosif, N., Perry, R., Poulter, N., Osman, K., Vatovec, S., Harper, A., Franklin, C. and Franklin-Tong, V. (2009) Identification of the Pollen Self-incompatibility Determinant in Papaver rhoeas. Nature, 459. pp. 992-995. ISSN Print: 0028-0836 Online: 1476-4687

Abstract

Higher plants produce seed through pollination, using specific interactions between pollen and pistil. Self-incompatibility is an important mechanism used in many species to prevent inbreeding; it is controlled by a multi-allelic S locus1,2. ‘Self’ (incompatible) pollen is discriminated from ‘non-self’ (compatible) pollen by
interaction of pollen and pistil S locus components, and is subsequentlyinhibited. In Papaver rhoeas, the pistil S locus product is a small protein that interacts with incompatible pollen, triggering a Ca21-dependent signalling network, resulting in pollen inhibition and programmed cell death3–7. Here we have cloned three alleles of a highly polymorphic pollen-expressed gene, PrpS (Papaver rhoeas
pollen S), from Papaver and provide evidence that this encodes the pollen S locus determinant. PrpS is a single-copy gene linked to the pistil S gene (currently called S, but referred to hereafter as PrsS for Papaver rhoeas stigma S determinant). Sequence analysis indicates
that PrsS and PrpS are equally ancient and probably co-evolved. PrpS encodes a novel 20-kDa protein. Consistent with predictions that it is a transmembrane protein, PrpS is associated with the plasma membrane. We show that a predicted extracellular loop segment of PrpS interacts with PrsS and, using PrpS antisense oligonucleotides, we demonstrate that PrpS is involved in S-specific inhibition of incompatible pollen. Identification of PrpS represents a major advance in our understanding of the Papaver self-incompatibility system. As a novel cell–cell recognition determinant it contributes to the available information concerning the origins and evolution of cell–cell recognition systems involved in discrimination between self and non-self, which also include histocompatibility systems in primitive chordates
and vertebrates.

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