In this study, seven ZmARF genes, including ZmARF1, 10, 13, 14, 18, 22 and 25, appeared to be constitutively expressed in developing embryos, whereas the transcripts of other ZmARF genes exhibited dynamic expression patterns, suggesting the partitioning of functions between these genes in embryo development.
The fact that duplicate genes for TPS exist implies a partitioning of function between the two paralogues [ 49], indeed as will be seen below, there is differential expression of the two genes in M. arctica under dehyrating conditions.
This evolution can be interpreted according to the sub-neofunctionalization model of gene evolution [ 2- 5], which proposes that the partitioning of function between the duplicated genes alters the selective environment at each locus, resulting in structural fine-tuning or adaptation of the encoded proteins by positive selection.
Further, we show that the evolutionary history of the Perissodini is characterized by an accentuation of craniofacial laterality such that certain taxa show elaborate sided differences in craniofacial shape consistent with the sub-partitioning of function between sides of the head during attacks.
The evolution of new functions or the partitioning of existing functions between gene copies are potential outcomes for any duplicate gene pair and may lead to the selection-driven preservation of both copies (Lynch and Force 2000).
Therefore, if these sequences really represent divergent paralogs, it is not clear, whether they underwent non-functionalization (silencing by degenerative mutations), neofunctionalization (non-synonymous substitutions providing a beneficial function) or subfunctionalization (partitioning of ancestral functions between duplicates) [ 70].
In cases of selection three major outcomes have been described: evolution of a new beneficial function in one duplicate (neofunctionalization), partitioning of ancestral functions between the duplicates (subfunctionalization), or conservation of ancestral function(s) in both duplicates (gene conservation) [ 2, 5– 7].
This scenario is consistent with previously observed asymmetric rate of evolution between duplicate genes (Kim and Yi 2006), which is usually explained by differences in expression levels and relaxed purifying selection due to the partitioning of ancestral functions between duplicates.
Genes that are differentially expressed during these time course experiments have expression patterns consistent with a very low rate of subfunctionalization (partition of ancestral functions between duplicated genes) in particular since the most recent polyploidization event.
Subfunctionalization can take the form of partitioning protein function between duplicates or, perhaps more commonly, partitioning of gene expression, so that duplicates have complementary expression patterns (Prince and Pickett 2002).
Subfunctionalization, the partitioning of ancestral functions, is the loss of different ancestral functions in different descendants.
