Unisexual flowers provide a useful system for studying plant sex determination. In cucumber (Cucumis sativus L.), three major Mendelian loci control unisexual flower development, Female (F), androecious [a; 1-aminocyclopropane-1-carboxylate {ACC} synthase 11, acs11], and Monoecious (M; ACS2), referred to here as the Female, Androecious, Monoecious (FAM) model, in combination with two genes, gynoecious (g, the WIP family C2H2 zinc finger transcription factor gene WIP1) and the ethylene biosynthetic gene ACC oxidase 2 (ACO2). The F locus, conferring gynoecy and the potential for increasing fruit yield, is defined by a 30.2-kb tandem duplication containing three genes. However, the gene that determines the Female phenotype, and its mechanism, remains unknown. Here, we created a set of mutants and revealed that ACS1G is responsible for gynoecy conferred by the F locus. The duplication resulted in ACS1G acquiring a new promoter and expression pattern; in plants carrying the F locus duplication, ACS1G is expressed early in floral bud development, where it functions with ACO2 to generate an ethylene burst. The resulting ethylene represses WIP1 and activates ACS2 to initiate gynoecy. This early ACS1G expression bypasses the need for ACS11 to produce ethylene, thereby establishing a dominant pathway for female floral development. Based on these findings, we propose a model for how these ethylene biosynthesis genes cooperate to control unisexual flower development in cucumber.
Hydrogen peroxide (H2O2) plays important roles in plant development. Adventitious root (AR), lateral bud (LB) and callus formation are important traits for plants. Here, a gene encoding respiratory burst oxidase homologs B (PdeRBOHB) from poplar line “NL895” (Populus. deltoides × P. euramericana) was predicted to be involved in H2O2 accumulation and its reduced expression (RE) transgenic lines were generated. H2O2 content was decreased, and the development of AR, LB and callus was inhibited, in RE PdeRBOHB lines. A gene encoding PdeWRKY75 was identified as the positive upstream transcription factor (TF) for PdeRBOHB. This regulation was confirmed by dual luciferase reporter assay, GUS transient expression analysis and electrophoretic mobility shift assay (EMSA). In the RE PdeWRKY75 lines, H2O2 content was decreased and the development of AR, LB and callus development was inhibited, while in the over expression (OE) lines, H2O2 content was increased and the development of AR and LB was inhibited, but callus formation was enhanced. Additionally, RE PdeRBOHB inhibited the expression of PdeWRKY75, while exogenous application of H2O2 showed the opposite effect. All of these results suggested that PdeWRKY75 and PdeRBOHB are part of a regulatory module in H2O2 accumulation, which is involved in the regulation of multiple biological processes.
The Chinese tallow tree (Triadica sebifera) can produce oil with high content of unsaturated fatty acids in seeds and shows attractive leaf color in autumn and winter. Here, the 739 Mb chromosome-scale genome sequence of the Chinese tallow tree was assembled and it reveals the Chinese tallow tree is a tetraploid. Numerous genes related to nutrition assimilation, energy utilization, biosynthesis of secondary metabolites and resistance significantly expanded or are specific to the Chinese tallow tree. These genes would enable the Chinese tallow tree to obtain high adaptability. More genes in fatty acids biosynthesis in its genome, especially for unsaturated fatty acids biosynthesis, and higher expression of these genes in seeds would be attributed to its high content of unsaturated fatty acids. Cyanidin 3-O-glucoside was identified as the major component of anthocyanin in red leaves. All structural genes in anthocyanin biosynthesis show significantly higher expression in red leaves than in green leaves. Transcription factors, seven MYB and one bHLH, were predicted to regulate these anthocyanin biosynthesis genes. Collectively, we provided insight into the polyploidization, high adaptability and biosynthesis of the high content of unsaturated fatty acids in seeds and anthocyanin in leaves for the Chinese tallow tree.
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