Inheritance of hetero-diploid pollen S-haplotype in self-compatible tetraploid Chinese cherry (Prunus pseudocerasus Lindl)

Abstract

The breakdown of self-incompatibility, which could result from the accumulation of non-functional S-haplotypes or competitive interaction between two different functional S-haplotypes, has been studied extensively at the molecular level in tetraploid Rosaceae species. In this study, two tetraploid Chinese cherry (Prunus pseudocerasus) cultivars and one diploid sweet cherry (Prunus avium) cultivar were used to investigate the ploidy of pollen grains and inheritance of pollen-S alleles. Genetic analysis of the S-genotypes of two intercross-pollinated progenies showed that the pollen grains derived from Chinese cherry cultivars were hetero-diploid, and that the two S-haplotypes were made up of every combination of two of the four possible S-haplotypes. Moreover, the distributions of single S-haplotypes expressed in self- and intercross-pollinated progenies were in disequilibrium. The number of individuals of the two different S-haplotypes was unequal in two self-pollinated and two intercross-pollinated progenies. Notably, the number of individuals containing two different S-haplotypes (S1- and S5-, S5- and S8-, S1- and S4-haplotype) was larger than that of other individuals in the two self-pollinated progenies, indicating that some of these hetero-diploid pollen grains may have the capability to inactivate stylar S-RNase inside the pollen tube and grow better into the ovaries.

Figure 1. Alignment of the deduced amino acid sequences of S-RNases from Chinese cherry and other Prunus species.

Asterisks, dot, and dashes indicate conserved amino acid sites, conservative substitutions, and gaps, respectively. The five conserved (C1, C2, C3, RC4 and C5) and hypervariable (RHV) regions are underlined.

Figure 2. Alignment of the deduced amino acid sequences of SFBs from Chinese cherry and other Prunus species.

Asterisks, dot, and dashes indicate conserved amino acid sites, conservative substitutions, and gaps, respectively. F-box motif, variable (V1 and V2) and hypervariable (HVa and HVb) regions are underlined.

Figure 3. Expression patterns of SFBs in two cultivars of Chinese cherry.

RT-PCR was performed using total RNA with primers to detect transcripts of SFB and Actin genes. S, P and L stand for style, pollen and leaf RNA with reverse transcriptase, respectively; G is genomic DNA and M is ladder marker. a. PCR amplification with primers ActF and ActR; b. PCR amplification with primers PsSFB-F1 and PsSFB-R1.

Figure 4. Schematic representation of the S locus of four S-haplotypes.

Black and white boxes represent exons and intergenic region, respectively. Double slashes show the regions which have not been determined in this study. The positions of the primers (Table S2 in File S1) used in the present study are indicated by arrows.