Abstract
BackgroundPear fruit exhibit a single sigmoid pattern during development, while peach and strawberry fruits exhibit a double sigmoid pattern. However, little is known about the differences between these two patterns.ResultsIn this study, fruit weights were measured and paraffin sections were made from fruitlet to maturated pear, peach, and strawberry samples. Results revealed that both single and double sigmoid patterns resulted from cell expansion, but not cell division. Comparative transcriptome analyses were conducted among pear, peach, and strawberry fruits at five fruit enlargement stages. Comparing the genes involved in these intervals among peaches and strawberries, 836 genes were found to be associated with all three fruit enlargement stages in pears (Model I). Of these genes, 25 were located within the quantitative trait locus (QTL) regions related to fruit weight and 90 were involved in cell development. Moreover, 649 genes were associated with the middle enlargement stage, but not early or late enlargement in pears (Model II). Additionally, 22 genes were located within the QTL regions related to fruit weight and 63 were involved in cell development. Lastly, dual-luciferase assays revealed that the screened bHLH transcription factors induced the expression of cell expansion-related genes, suggesting that the two models explain the single sigmoid pattern.ConclusionsSingle sigmoid patterns are coordinately mediated by Models I and II, thus, a potential gene regulation network for the single sigmoid pattern was proposed. These results enhance our understanding of the molecular regulation of fruit size in Rosaceae.
Highlights
Pear fruit exhibit a single sigmoid pattern during development, while peach and strawberry fruits exhibit a double sigmoid pattern
Cyclin, RNA polymerase II transcription, and mitogen-activated protein kinase kinase kinase are involved in the cell cycle [19,20,21], xyloglucan galactosyltransferase, glycosyltransferase, cellulose synthase, β-galactosidase, and microtubule-associated proteins are associated with cell wall metabolism [22,23,24,25], and transcription factors, including basic region/leucine zipper motif [26], NAM/ATAF1/2/CUC2 (NAC) [27], v-myb avian myeloblastosis viral oncogene homolog (MYB) [28], basic/helix-loop-helix [29], and WRKY [30], are components of the fruit size regulation network
The cell size changed little before 42, 21, and 19 days after full blooming (DAFB), respectively, and the cell expansion was happened (Fig. 2). These results revealed that pear, peach, and strawberry fruits underwent extensive cell division before 42, 21, and 19 DAFB, respectively, underwent cell enlargement
Summary
Pear fruit exhibit a single sigmoid pattern during development, while peach and strawberry fruits exhibit a double sigmoid pattern. Within the Rosaceae, different fleshy fruit types showed two different fruit growth patterns. Pome fruits such as apple and pear exhibit a single sigmoid pattern in which fruits undergo extensive cell division during the first few weeks immediately following fertilization, after which almost all growth is due to cell enlargement [1,2,3,4]. The distinction between single and double sigmoid patterns is whether a slow-growth period occurs during fruit enlargement. Little is known about the genes that control fruit size, with the exception of genes involved in the cell cycle, cell wall metabolism, cytochrome, and ubiquitin [13, 17, 18]. Cyclin, RNA polymerase II transcription, and mitogen-activated protein kinase kinase kinase are involved in the cell cycle [19,20,21], xyloglucan galactosyltransferase, glycosyltransferase, cellulose synthase, β-galactosidase, and microtubule-associated proteins are associated with cell wall metabolism [22,23,24,25], and transcription factors, including basic region/leucine zipper motif (bZIP) [26], NAM/ATAF1/2/CUC2 (NAC) [27], v-myb avian myeloblastosis viral oncogene homolog (MYB) [28], basic/helix-loop-helix (bHLH) [29], and WRKY [30], are components of the fruit size regulation network
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