Two Likely Auto-Tetraploidization Events Shaped Kiwifruit Genome and Contributed to Establishment of the Actinidiaceae Family

The genome of kiwifruit (Actinidia chinensis) was sequenced previously, the first in the Actinidiaceae family. It was shown to have been affected by polyploidization events, the nature of which has been elusive. Here, we performed a reanalysis of the genome and found clear evidence of 2 tetraploidization events, with one occurring ∼50–57 million years ago (Mya) and the other ∼18–20 Mya. Two subgenomes produced by each event have been under balanced fractionation. Moreover, genes were revealed to express in a balanced way between duplicated copies of chromosomes. Besides, lowered evolutionary rates of kiwifruit genes were observed. These findings could be explained by the likely auto-tetraploidization nature of the polyploidization events. Besides, we found that polyploidy contributed to the expansion of key functional genes, e.g., vitamin C biosynthesis genes. The present work also provided an important comparative genomics resource in the Actinidiaceae and related families.