Nuclear–Cytoplasmic Coevolution Analysis of RuBisCO in Synthesized Cucumis Allopolyploid

Allopolyploids are often faced with the challenge of maintaining well-coordination between nuclear and cytoplasmic genes inherited from different species. The synthetic allotetraploid Cucumis × hytivus is a useful model to explore cytonuclear coevolution. In this study, the sequences and expression of cytonuclear enzyme complex RuBisCO as well as its content and activity in C. × hytivus were compared to its parents to explore plastid–nuclear coevolution. The plastome-coded rbcL gene sequence was confirmed to be stable maternal inheritance, and parental copy of nuclear rbcS genes were both preserved in C. × hytivus. Thus, the maternal plastid may interact with the biparentally inherited rbcS alleles. The expression of the rbcS gene of C-homoeologs (paternal) was significantly higher than that of H-homoeologs (maternal) in C. × hytivus (HHCC). Protein interaction prediction analysis showed that the rbcL protein has stronger binding affinity to the paternal copy of rbcS protein than that of maternal copy in C. × hytivus, which might explain the transcriptional bias of the rbcS homoeologs. Moreover, both the activity and content of RuBisCO in C. × hytivus showed mid-parent heterosis. In summary, our results indicate a paternal transcriptional bias of the rbcS genes in C. × hytivus, and we found new nuclear–cytoplasmic combination may be one of the reasons for allopolyploids heterosis.

Genomic imprinting and cancer: Remembering the parental origin

Genomic imprinting results in only one copy of a diploid pair of alleles being expressed in a parentof-origin-specific manner. The ‘imprint’ encodes a memory of whether a gene came through the maternal or paternal line and contains the information that decides which parental copy will be active or silent. Imprints are established in the developing gametes, passed on to the next generation after fertilization where they are read and maintained in the somatic cells or erased and reset in the germ cells. The components of the ‘memory’ are a combination of epigenetic features such as DNA methylation, post-translational histone modifications and protein/RNA factors that can bind to DNA and label the genes such that a cell's transcription machinery can distinguish between maternal and paternal alleles. Most imprinted genes are associated with sequences that are methylated on only one parental allele, known as differentially methylated regions (DMRs).