Nuclear–Cytoplasmic Coevolution Analysis of RuBisCO in Synthesized Cucumis Allopolyploid

Abstract

Allopolyploids are often faced with the challenge of maintaining well-coordination between nuclear and cytoplasmic genes inherited from different species. The synthetic allotetraploid <i>Cucumis × hytivus</i> 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 <i>C. × hytivus</i> were compared to its parents to explore plastid-nuclear coevolution. The plastome-coded <i>rbcL</i> gene sequence was confirmed to be stable maternal inheritance, and parental copy of nuclear <i>rbcS</i> genes were both preserved in <i>C. × hytivus.</i> Thus, the maternal plastid may interact with the biparentally inherited <i>rbcS</i> alleles. The expression of the <i>rbcS</i> gene of C-homoeologs (paternal) was significantly higher than that of H-homoeologs (maternal) in <i>C. × hytivus</i> (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 <i>C. × hytivus</i>, which might explain the transcriptional bias of the <i>rbcS</i> homoeologs. Moreover, both the activity and content of RuBisCO in <i>C. × hytivus</i> showed mid-parent heterosis. In summary, our results indicate a paternal transcriptional bias of the <i>rbcS</i> genes in <i>C. × hytivus</i>, and we found new nuclear-cytoplasmic combination may be one of the reasons for allopolyploids heterosis.