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.
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