Molecular and cellular characteristics of hybrid vigour in a commercial hybrid of Chinese cabbage

Abstract

BackgroundHeterosis or hybrid vigour is a phenomenon in which hybrid progeny exhibit superior performance compared to their parental inbred lines. Most commercial Chinese cabbage cultivars are F1 hybrids and their level of hybrid vigour is of critical importance and is a key selection criterion in the breeding system.ResultsWe have characterized the heterotic phenotype of one F1 hybrid cultivar of Chinese cabbage and its parental lines from early- to late-developmental stages of the plants. Hybrid cotyledons are larger than those of the parents at 4 days after sowing and biomass in the hybrid, determined by the fresh weight of leaves, is greater than that of the larger parent line by approximately 20 % at 14 days after sowing. The final yield of the hybrid harvested at 63 days after sowing is 25 % greater than the yield of the better parent. The larger leaves of the hybrid are a consequence of increased cell size and number of the photosynthetic palisade mesophyll cells and other leaf cells. The accumulation of plant hormones in the F1 was within the range of the parental levels at both 2 and 10 days after sowing. Two days after sowing, the expression levels of chloroplast-targeted genes in the cotyledon cells were upregulated in the F1 hybrid relative to their mid parent values. Shutdown of chlorophyll biosynthesis in the cotyledon by norflurazon prevented the increased leaf area in the F1 hybrid.ConclusionsIn the cotyledons of F1 hybrids, chloroplast-targeted genes were upregulated at 2 days after sowing. The increased activity levels of this group of genes suggested that their differential transcription levels could be important for establishing early heterosis but the increased transcription levels were transient. Inhibition of the photosynthetic process in the cotyledon reduced heterosis in later seedling stages. These observations suggest early developmental events in the germinating seedling of the hybrid may be important for later developmental vigour and yield advantage.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0734-3) contains supplementary material, which is available to authorized users.

Genome-wide analysis of heterosis-related genes in non-heading Chinese cabbage

“…These results indicated that the early stage of growth may determine the heterosis phenotypes in F 1 cultivar Shulu. The highest difference between two parents also expected that the genetic difference on the gene expression regulation will be different from those obtained from heading-type Chinese cabbage, in which they have used similar parents (Saeki et al 2016). Expression pattern analysis revealed that non-additive expression was prominent compared with additive expression in non-heading type (Table 1), different from the previous results for heading type Chinese cabbage (B. rapa ssp.…”

“…Expression pattern analysis revealed that non-additive expression was prominent compared with additive expression in non-heading type (Table 1), different from the previous results for heading type Chinese cabbage (B. rapa ssp. pekinensis) (Saeki et al 2016). Saeki et al (20106) reported that most genes show an additive expression pattern, and any expression level differences between parental lines were maintained in F 1 hybrids.…”

“…Gene interactions, such as dominance, overdominance, pseudooverdominance, and epistasis, have therefore been suggested to explain heterosis phenotypes (Lippman and Zamir 2007;Charlesworth et al 2009). Recent molecular analyses of transcriptomes, proteomes, and metabolomes with two parents and hybrids have led to the appreciation of new aspects on the establishment of hybrid vigor, such as epigenetic effects (Groszmann et al 2011 and2013;Baranwal et al 2012;Schnable and Springer 2013;Li et al 2016;Saeki et al 2016)]. …”

Chlorophyll fluorescence imaging reveals genetic variation and loci for a photosynthetic trait in diploid potato

“…Little is known about the implications of photosynthetic traits on hybrid vigor. An increase in photosynthetic cell size and number, as well as the rate of photosynthesis per unit leaf area, has been suggested to contribute to hybrid vigor (Monma and Tsunoda , Wang et al ); changes in transcription patterns were shown to affect photosynthetic genes, especially in early developmental stages (Fujimoto et al , Saeki et al ). Two of three hybrid plants used in this study (Hybrids 1 and 2) had a significantly higher Φ PSII than their female parents; this points to a heterosis effect on photosynthesis in potato.…”

In Arabidopsis hybrids and Hybrid Mimics, up‐regulation of cell wall biogenesis is associated with the increased plant size

“…The gain in the hybrid plants compared with the performance of parents is referred to as hybrid vigor or heterosis. In Arabidopsis (Fujimoto, Taylor, Shirasawa, Peacock, & Dennis, 2012;Groszmann et al, 2014), maize (Birchler, Auger, & Riddle, 2003;Li, Yang, et al, 2017), and Chinese cabbage (Saeki et al, 2016), hybrid plants have an architecture with larger leaves and the plants are taller compared with the parents. The increased leaf size is due to increased number and size of leaf cells (Fujimoto et al, 2012;Groszmann et al, 2014).…”