Allelic diversity of S-RNase alleles in diploid potato species.

Daniel K Dzidzienyo,Timothy P Robbins,Glenn J Bryan,Gail Wilde

doi:10.1007/s00122-016-2754-7

Abstract

Key messageThe S-ribonuclease sequences of 16 S-alleles derived from diploid types of Solanum are presented. A phylogenetic analysis and partial phenotypic analysis support the conclusion that these are functional S-alleles.S-Ribonucleases (S-RNases) control the pistil specificity of the self-incompatibility (SI) response in the genus Solanum and several other members of the Solanaceae. The nucleotide sequences of S-RNases corresponding to a large number of S-alleles or S-haplotypes have been characterised. However, surprisingly, few S-RNase sequences are available for potato species. The identification of new S-alleles in diploid potato species is desirable as these stocks are important sources of traits such as biotic and abiotic resistance. S-RNase sequences are reported here from three distinct diploid types of potato: cultivated Solanum tuberosum Group Phureja, S. tuberosum Group Stenotomum, and the wild species Solanum okadae. Partial S-RNase sequences were obtained from pistil RNA by RT-PCR or 3′RACE (Rapid Amplification of cDNA Ends) using a degenerate primer. Full-length sequences were obtained for two alleles by 5′RACE. Database searches with these sequences identified 16 S-RNases in total, all of which are novel. The sequence analysis revealed all the expected features of functional S-RNases. Phylogenetic analysis with selected published S-RNase and S-like-RNase sequences from the Solanaceae revealed extensive trans-generic evolution of the S-RNases and a clear distinction from S-like-RNases. Pollination tests were used to confirm the self-incompatibility status and cross-compatibility relationships of the S. okadae accessions. All the S. okadae accessions were found to be self-incompatible as expected with crosses amongst them exhibiting both cross-compatibility and semi-compatibility consistent with the S-genotypes determined from the S-RNase sequence data. The progeny analysis of four semi-compatible crosses examined by allele-specific PCR provided further confirmation that these are functional S-RNases.Electronic supplementary materialThe online version of this article (doi:10.1007/s00122-016-2754-7) contains supplementary material, which is available to authorized users.

Highlights

The majority of flowering plants are hermaphrodite, and their reproductive organs are located in close proximity, a feature which might have imposed self-pollination and, subsequently, self-fertilisation on angiosperms
A compatible or semi-compatible reaction will occur when at least one of the haplotypes expressed in the pollen and pistils do not match
If the two parents differ by just one haplotype, a semi-compatible reaction will occur, and all the pollen tubes carrying the shared haplotype will be arrested, whilst those carrying the unique haplotype will be accepted

Summary

Introduction

The majority of flowering plants are hermaphrodite, and their reproductive organs are located in close proximity, a feature which might have imposed self-pollination and, subsequently, self-fertilisation on angiosperms. The extensive study of GSI at the molecular level has revealed that it operates by two different mechanisms to achieve self-pollen recognition and rejection. One of these is the stylar ribonuclease (S-RNase) mechanism which has been initially identified and characterised in members of the Solanaceae, and later in the Rosaceae, Plantaginaceae and most recently in the Rubiaceae (Kao and McCubbin 1996; Nowak et al 2011; Asquini et al 2011). The pistil specificity of plant families exhibiting the S-RNase-based GSI system is controlled by polymorphic glycoproteins which are ribonucleases (S-RNases) and that have confirmed ribonuclease activity (Bredemeijer and Blass 1981; Anderson et al 1986; McClure et al 1989). Transgenic experiments in both petunia and tobacco have established that the S-RNase is the sole determinant of pistil specificity (Lee et al 1994; Murfett et al 1994)

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Conclusion