Abstract
The morphogenesis of gynoecium is crucial for propagation and productivity of fruit crops. For trioecious papaya (Carica papaya), highly differentiated morphology of gynoecium in flowers of different sex types is controlled by gene networks and influenced by environmental factors, but the regulatory mechanism in gynoecium morphogenesis is unclear. Gynodioecious and dioecious papaya varieties were used for analysis of differentially expressed genes followed by experiments using auxin and an auxin transporter inhibitor. We first compared differential gene expression in functional and rudimentary gynoecium at early stage of their development and detected significant difference in phytohormone modulating and transduction processes, particularly auxin. Enhanced auxin signal transduction in rudimentary gynoecium was observed. To determine the role auxin plays in the papaya gynoecium, auxin transport inhibitor (N-1-Naphthylphthalamic acid, NPA) and synthetic auxin analogs with different concentrations gradient were sprayed to the trunk apex of male and female plants of dioecious papaya. Weakening of auxin transport by 10 mg/L NPA treatment resulted in female fertility restoration in male flowers, while female flowers did not show changes. NPA treatment with higher concentration (30 and 50 mg/L) caused deformed flowers in both male and female plants. We hypothesize that the occurrence of rudimentary gynoecium patterning might associate with auxin homeostasis alteration. Proper auxin concentration and auxin homeostasis might be crucial for functional gynoecium morphogenesis in papaya flowers. These results will lead to further investigation on the auxin homeostasis and gynoecium morphogenesis in papaya.
Highlights
In angiosperms, 89% species are hermaphrodite, 5% are monoecy, and 6% are dioecy[1]
Our aim is to identify the regulatory mechanisms related to gynoecium morphogenesis in papaya through the clues of metabolism changes by differential gene expression analysis
Differential gene expression pattern between functional and rudimentary gynoecium revealed that gynoecium morphologenesis and development are associated with three main biological processes, including (i) response to stimulus which may induce abnormalities, unbalanced phytohormone distribution, ectopic transcription factor modulation, and aberrant cell proliferation growth; (ii) response to growth and development, which may be associated with female gametophyte and fertilization-independent development; and (iii) reponse to phytohormones
Summary
Male flowers arose due to the occurrence of female sterility (gynoecium abortion) and male fertility in hermaphroditic flower ancestors. It was evolutionarily benefited from male–female mating strategies to maintain offspring genetic diversity by promoting pollen dispersal in population, a seemingly futile strategies for agriculture[2]. The environmental changes coupled with phytohormones imbalance would induce floral organ abortion[9]. All of these have attracted biologists to understand the possible inherited and environmental regulatory mechanism of gynoecium morphogenesis in plants
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