To develop a new system for inducible male sterility without any modification of the floral architecture in tobacco plants, a mutated ethylene receptor gene Cm-ERS1/H70A was fused either to the tobacco Nin88 promoter known to function mainly in the tapetum and microspore or to the CaMV 35S promoter known to be a constitutive promoter. The fusion genes pNin88::Cm-ERS1/H70A and p35S::Cm-ERS1/H70A were introduced in tobacco plants, which generated two independent transformants. Transformants with 35S::Cm-ERS1/H70A produced less normal pollen and had modified floral architecture while those with Nin88::Cm-ERS1/H70A produced less normal pollen without modification of floral architecture. Histological observations of anthers at stage 2 showed that tapetum degeneration in NH70A #8 and H70A #2 transformants occurred later than in wild types, strongly indicating that the expression of the mutated gene was involved in this delay. These results suggest that the tapetum-specific expression of a mutated ethylene receptor gene is a potential strategy for inducing male sterility in transgenic plants.
"At present, ethylene is suggested to be a mediator of PCD in plants (Woltering and others 1999). Introduction of a constitutively active form of the melon ethylene receptor into tobacco under the control of an anther-specific promoter was shown to cause a reduced number of pollen grains and delay in the PCD of tapetal cells (Takada and others 2006). Because ethylene is believed to be a key regulator of PCD (Gunawardena 2008), these observations suggest that ethylene is involved in the PCD of tapetal cells. "
[Show abstract][Hide abstract] ABSTRACT: The time courses of 1-aminocyclopropane-1-carboxylic acid (ACC) content and ethylene production in developing anthers of petunia
fertile and sterile lines and the effects of exogenously applied ethylene and an inhibitor of ethylene action, 2,5-norbornadiene
(NBD), on male gametophyte development and germination were investigated. Fertile male gametophyte development was accompanied
by two peaks of ethylene production by anther tissues. The first peak occurred during microspore development simultaneously
with degeneration of both tapetal tissues and middle layers of the anther wall. The second peak coincided with maturation
and dispersal of pollen grains. The mature pollen is characterized by a high ACC content (up to 300nmol/g). Exogenously applied
ethylene (1–100ppm) induced degradation of gametophytic generation at the meiosis stage. NBD completely inhibited anther
development at the early stages of its development and delayed anther dehiscence. In anther tissues of the petunia sterile
line, tenfold higher ethylene production was observed at the meiosis stage compared to that in fertile male gametophytes and
this correlated with degeneration of both microsporocytes and tapetal tissues. In vitro male gametophyte germination was accompanied
by an increase of ethylene production, whereas NBD completely blocked male gametophyte germination. These results suggest
that ethylene is an important factor in male gametophyte development and germination.
KeywordsEthylene–ACC–Anther–Male gametophyte–Development–Male sterility
[Show abstract][Hide abstract] ABSTRACT: External treatment with ethylene had indicated earlier that this hormone is the main factor controlling sex determination
in Cucurbita pepo. Up to now, however, there was no genetic evidence that supported the relationship between ethylene production, or perception,
and sexual expression in this species. Here we demonstrate that the extreme male phenotype of the Vegetable Spaghetti (Veg) inbred line of C. pepo subspecies pepo is determined by a major gene that confers reduced ethylene sensitivity in plants. The production of female flowers in the
Veg line is very delayed and reduced with respect to the contrasting Bolognese (Bog) line, ranging between 5 and 35% of female flowers per plant. This enhanced maleness trait segregates as a single gene in
the F2 and backcross (BC) generations, and co-segregates with a weak ethylene-insensitive phenotype in the F2 population, suggesting that the gene responsible for the Veg phenotype could be the result of a mutation in a receptor or response gene for ethylene. Although the etiolated seedlings
of the Veg line, and the most androecious plants in the F2 generation, produce more ethylene than those of the contrasting line, they are less sensitive to this hormone, as indicated
by a weaker triple response and a delayed abscission of ethylene-treated male flowers. Given that the sexual phenotype of
F2 plants is correlated with ethylene sensitivity, with the more sensitive plants producing the higher number of female flowers,
our results demonstrate that the ethylene response is directly involved in the control of sex determination in C. pepo. It regulates the induction of female flower production, and therefore the extension of the initial phase of development
in which the plant produces only male flowers, as well as the number of female flowers per plant.
-Sex expression-Ethylene production-Ethylene sensitivity
[Show abstract][Hide abstract] ABSTRACT: Efforts in hybrid breeding have made this technology one of the main factors contributing to the substantial global rise in
agricultural output over the last few decades. For hybrid breeding, an efficient pollination control system is necessary to
avoid the unwanted self-pollination or sib-pollination of the female parental line. This review will provide a historical
overview of pollination control systems and their use in hybrid crop breeding. We outline the prerequisites for commercial
hybrid breeding and summarize the most important non-biological and biological technologies. Our main focus is on hybrid systems
that are based on genetically engineered plants. We describe their suitability for pollination control, propagation of the
male-sterile crossing partner, fertility restoration and mixed planting. Additionally, we report on the latest findings in
the development of inducible sterility systems and various technologies that enable pollination control via metabolic engineering.
We discuss the pros and cons of the different pollination control strategies.
KeywordsHybrid breeding–Pollination control–Male sterility–Transgenic plants–Metabolic engineering
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