Fig. 5.

Effects of dynamic 3D architecture on hormone-related genes, cell proliferation and cell expansion. A, A diagram of hormones closely associated with plant growth. Red and gray arrows represent hormones beneficial and disadvantageous to plant growth, respectively. Hormones: CK, cytokinins; GA gibberellin; BR, brassinosteroids; SA, salicylic acid; ABA, abscisic acid; ETH, ethylene. B, Number of upregulated and downregulated hormone-related genes in F1 hybrids versus the MPV (Student’s t test, P < 0.05) related to auxin, CK, GA and BR. C, Comparison of hybrid gene expression and the MPV. The dotted line indicates a slope of 1, meaning that the MPV is equivalent to F1 gene expression. Red and gray dots indicate the genes that are more highly and more weakly expressed in the F1 hybrids versus the MPV, respectively. D, Examples of the relationship between 3D chromatin structure and plant-hormone-related gene expression. The first track shows the features of the Hi-C chromatin interaction. Strong interactions are shown in red and weak interactions are shown in blue. The second track shows the distribution of compartments: red, A; blue, B. The third track shows RNA-seq read coverage in the chosen region. The fourth track shows the genes in the chosen region. Red denotes hormone-related genes; red arrows represent genes that were more highly expressed in the F1 hybrids versus the MPV; purple arrows represent genes that were expressed at lower levels in the F1 hybrids versus the MPV. E, Depiction of the regulatory network of auxin and auxin-related genes. Heat map of auxin-related gene expression: dark red and dark blue represent high and low gene expression levels, respectively. Orange and blue triangles around auxin represent relatively high hormone levels in superior hybrids and relatively low hormone levels in inferior hybrids, respectively. The bottom arrow indicates the four phases of the cell cycle. F, The second leaf areas of parents and hybrids. G, Paradermal optical sections of the palisade mesophyll (PM) layer showing the larger cells of superior heterosis sets. H and I, Measurements of PM cell size (H) and estimated cell number (I) in the hybrids. (F, H and I) The percentage above the bar is the MPH (mid-parent heterosis) ratio in the corresponding F1 hybrid. Red asterisks indicate significant differences from the MPV, and black asterisks indicate values above the BPV (better parent value). Statistical comparisons among the J-M−X−JM−JX (uppercase blue letters) and F-O-V-FO-FV (uppercase red letters) are shown, and categories with different letters are significantly different from the others (Student’s t test, P < 0.01). All error bars are S.E.M. n = 10–14. J, Relative contributions of the increases in cell size and cell number to the larger leaves of the hybrids. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)