1. CIQUIBIC, Departamento de Quimica Biologica, Facultad de Ciencias Quimicas, Universidad Nacional de Cordoba, Ciudad Universitaria, 5000 Cordoba, Argentina
2. Division of Biochemistry, 105 Life Sciences Center, 1201 E. Rollins Street, Columbia, Missouri 65211, USA
3. Division of Biological Sciences, 2 Tucker Hall, Columbia, Missouri 65211, USA
4. Department of Plant Biology, 4505 Miller Plant Sciences Building, Athens, Georgia 30602, USA
5. Departamento de Biologia, Facultad de Ciencias, Universidad Nacional Autonoma de Mexico, Ave Universidad y Copilco, Mexico D.F. 04510, Mexico
6. Departamento de Bioquimica, Facultad de Quimica, Universidad Nacional Autonoma de Mexico, Ave Universidad y Copilco, Mexico D.F. 04510, Mexico
7. *These authors contributed equally to this work

Correspondence to: Bruce McClure² Correspondence and requests for materials should be addressed to B.M. (Email: mcclureb@missouri.edu).

Abstract

Pollen–pistil interactions are crucial for controlling plant mating. For example, S-RNase-based self-incompatibility prevents inbreeding in diverse angiosperm species. S-RNases are thought to function as specific cytotoxins that inhibit pollen that has an S-haplotype that matches one of those in the pistil. Thus, pollen and pistil factors interact to prevent mating between closely related individuals. Other pistil factors, such as HT-B, 4936-factor and the 120 kDa glycoprotein, are also required for pollen rejection but do not contribute to S-haplotype-specificity per se. Here we show that S-RNase is taken up and sorted to a vacuolar compartment in the pollen tubes. Antibodies to the 120 kDa glycoprotein label the compartment membrane. When the pistil does not express HT-B or 4936-factor, S-RNase remains sequestered, unable to cause rejection. Similarly, in wild-type pistils, compatible pollen tubes degrade HT-B and sequester S-RNase. We suggest that S-RNase trafficking and the stability of HT-B are central to S-specific pollen rejection.

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