1. School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK

Correspondence to: Vernonica E. Franklin-Tong¹ Email: v.e.franklin-tong@bham.ac.uk

Abstract

Sexual reproduction in many angiosperm plants involves self-incompatibility (SI), which is one of the most important mechanisms to prevent inbreeding. SI is genetically controlled by the S-locus, and involves highly specific interactions during pollination between pollen and the pistil on which it lands. This results in the rejection of incompatible ('self') pollen, whereas compatible ('non-self') pollen is allowed to fertilize the plant¹. In Papaver rhoeas, S-proteins encoded by the stigma component of the S-locus interact with incompatible pollen, triggering a Ca²⁺-dependent signalling network^{2, 3, 4, 5, 6, 7}, resulting in the inhibition of pollen-tube growth. Programmed cell death (PCD) is a mechanism used by many organisms to destroy unwanted cells in a precisely regulated manner^{8, 9, 10}. Here we show that PCD is triggered by SI in an S-specific manner in incompatible pollen. This provides a demonstration of a SI system using PCD, revealing a novel mechanism to prevent self-fertilization. Furthermore, our data reveal that the response is biphasic; rapid inhibition of pollen-tube growth is followed by PCD, which is involved in a later 'decision-making' phase, making inhibition irreversible.

1. School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK

Correspondence to: Vernonica E. Franklin-Tong¹ Email: v.e.franklin-tong@bham.ac.uk

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