Abstract
Most germplasms of the biofuel plant Jatropha curcas are monoecious. A gynoecious genotype of J. curcas was found, whose male flowers are aborted at early stage of inflorescence development. To investigate the regulatory mechanism of transition from monoecious to gynoecious plants, a comparative transcriptome analysis between gynoecious and monoecious inflorescences were performed. A total of 3,749 genes differentially expressed in two developmental stages of inflorescences were identified. Among them, 32 genes were involved in floral development, and 70 in phytohormone biosynthesis and signaling pathways. Six genes homologous to KNOTTED1-LIKE HOMEOBOX GENE 6 (KNAT6), MYC2, SHI-RELATED SEQUENCE 5 (SRS5), SHORT VEGETATIVE PHASE (SVP), TERMINAL FLOWER 1 (TFL1), and TASSELSEED2 (TS2), which control floral development, were considered as candidate regulators that may be involved in sex differentiation in J. curcas. Abscisic acid, auxin, gibberellin, and jasmonate biosynthesis were lower, whereas cytokinin biosynthesis was higher in gynoecious than that in monoecious inflorescences. Moreover, the exogenous application of gibberellic acid (GA3) promoted perianth development in male flowers and partly prevented pistil development in female flowers to generate neutral flowers in gynoecious inflorescences. The arrest of stamen primordium at early development stage probably causes the abortion of male flowers to generate gynoecious individuals. These results suggest that some floral development genes and phytohormone signaling pathways orchestrate the process of sex determination in J. curcas. Our study provides a basic framework for the regulation networks of sex determination in J. curcas and will be helpful for elucidating the evolution of the plant reproductive system.
Highlights
Flowering plants show extreme diversity in their reproductive systems
In stage I, spanning 1–7 days from the formation of visible inflorescence buds, both female and male flowers could develop in gynoecious plants that is similar to the monoecious plants (Figure 1)
Transcriptome analysis showed that differentially expressed genes in pairwise stage II vs. I in monoecious inflorescence are far less than ones in gynoecious (Figure 4)
Summary
Flowering plants show extreme diversity in their reproductive systems. The determination of the environmental and genetic factors that control sexual diversification is a central problem in plant evolutionary biology (Barrett, 2002). Plant sex determination that leads to the physical separation of male and female reproductive organs plays a crucial role in the evolutionary process from hermaphroditic to unisexual flowers (Dellaporta and Calderon-Urrea, 1993; Tanurdzic and Banks, 2004). In order to facilitate outcrossing and more efficient allocation of resources to optimization of reproduction (Bawa, 1980; Thomson and Barrett, 1981), approximately 10% of angiosperm species have produced unisexual flower reproductive systems in dioecious and monoecious plant taxa (Yampolsky and Yampolsky, 1922). Hormonal, and environmental cues are involved in the regulation of sex determination in flowering plants (Aryal and Ming, 2014). Sex determination has evolved multiple times independently suggesting that various different genetic mechanisms underlie unisexual flower development (Ainsworth et al, 1998; Chuck, 2010; Diggle et al, 2011)
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