Abstract
Most varieties of persimmon (Diospyros kaki Thunb.) are gynoecious, while just a few are either monoecious, androgynomonoecious, or androecious. Persimmon flowers initially contain the original androecium and gynoecium followed by arrest of either pistil or stamen primordia before maturity. Abortion of inappropriate primordium in persimmon may be related to programmed cell death (PCD). To test this hypothesis, hematoxylin and eosin (H&E) staining, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay, cyt-c immunohistochemistry (IHC) assay, transmission electron microscopy (TEM) observation, and real-time quantitative polymerase chain reaction (RT-qPCR) were used to clarify the occurrence and molecular regulatory mechanism of PCD in male and female floral buds during the 14 days prior to the second crucial morphological stage when inappropriate sexual primordia were arrested to form unisexual flowers. Accordingly, dead cells in inappropriate sex organs were largely accumulated during the microsporocyte and macrosporocyte period of male and female floral buds, respectively. This may explain the abortion of inappropriate sex organs, leading to unisexual flowers. PCD is necessary for normal growth and development in persimmons, as dead cells could also be observed in the normal flower organs. High levels of a gene homologous to AMC9 may have accelerated the arrest of the pistil primordium during differentiation, leading to male unisexual flowers, and high levels of genes homologous to MeGI, BAG5, AifA, and HSP70 in female floral buds were positively correlated with the arrest of stamen primordium. Future studies may try to transform unisexual flowers into hermaphroditic flowers by the regulation of PCD artificially, which will be helpful to the controlled pollination experiments.
Highlights
Persimmon (Diospyros kaki Thunb.) is one of the most important temperate fruit species in China and has been widely cultivated for more than 2000 years [1]
Numerous microsporocytes with rich cytoplasm developed from the anther sporogonium, but the carpel primordium presented conspicuous changes closely related to programmed cell death (PCD) (Figure 3d,e; samples collected on April 14, 2017)
Surprisingly large areas of dead cells in the pistil primordium of the male flowers and the stamen primordium of the female flowers synchronously reached a peak at the microsporocyte and macrosporocyte period respectively, which may explain the abortion of inappropriate sex organs, leading to unisexual flowers
Summary
Persimmon (Diospyros kaki Thunb.) is one of the most important temperate fruit species in China and has been widely cultivated for more than 2000 years [1]. Agronomy 2020, 10, 234 improved cultivars and the limited popularity of the fruits among consumers due to their astringency; the large number of persimmon trees growing in China is an under-utilized resource [2]. The rare androecious type is occasionally found in wild persimmon (D. kaki) populations [3,4]. The lack of male flowers strongly restricts controlled pollination of persimmon, which can be used to potentially produce new cultivars with better economic traits. Research on sex differentiation of persimmon (D. kaki) to help control the sex type of flowers artificially has generated interest from the basic science community and economic stakeholders
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