Department of Biology and Geology, Research Centers CIAIMBITAL and CeiA3, University of Almería, Carretera Sacramento s/n, Almería, 04120, Spain.
Department of Plant Physiology, University of Granada, Avenida de Fuente Nueva s/n, Granada, 18071, Spain.
Plant J. 2020 Aug;103(4):1548-1560. doi: 10.1111/tpj.14846. Epub 2020 Jul 27.
Ethylene is the key regulator of sex determination in monoecious species of the family Cucurbitaceae. This hormone determines which individual floral meristems develop as female or male flowers and the female flowering transition. The sex determination genes discovered so far code for ethylene biosynthesis enzymes, but little is known about the importance of ethylene signaling components. In this paper we characterize two novel ethylene-insensitive mutations (etr1a-1 and etr1b) which block the female flowering transition of Cucurbita pepo; this makes plants produce male flowers indefinitely (androecy). Two missense mutations in the ethylene-binding domain of the ethylene receptors CpETR1A or CpETR1B were identified as the causal mutations of these phenotypes by using whole-genome resequencing. The distinctive phenotypes of single and double mutants for four etr mutations have demonstrated that the final level of ethylene insensitivity depends upon the strength and dosage of mutant alleles for at least three cooperating ETR genes, and that the level of ethylene insensitivity determines the final sex phenotype of the plant. The sex phenotype ranges from monoecy in ethylene-sensitive wild-type plants to androecy in the strongest ethylene-insensitive ones, via andromonoecy in partially ethylene-insensitive plants. The induction of female flowering transition was found to be associated with upregulation of CpACS11, CpACO2 and CpACS27, three ethylene biosynthesis genes required for female flower development. A model is proposed herein, integrating both ethylene biosynthesis and receptor genes into the genetic network which regulates sex determination in C. pepo.
乙烯是葫芦科雌雄同株物种性别决定的关键调节剂。这种激素决定了哪些个体花分生组织发育为雌花或雄花，以及雌性花的转变。迄今为止发现的性别决定基因编码乙烯生物合成酶，但对乙烯信号成分的重要性知之甚少。在本文中，我们描述了两个新的乙烯不敏感突变（etr1a-1 和 etr1b），它们阻止了南瓜的雌性花转变；这使得植物无限期地产生雄花（雌雄同体）。通过全基因组重测序，在乙烯受体 CpETR1A 或 CpETR1B 的乙烯结合域中发现了两个错义突变，这些突变是这些表型的因果突变。四个 etr 突变的单突变体和双突变体的独特表型表明，最终的乙烯不敏感水平取决于至少三个合作的 ETR 基因的突变等位基因的强度和剂量，并且乙烯不敏感水平决定了植物的最终性别表型。性表型范围从对乙烯敏感的野生型植物的雌雄同株到最强的乙烯不敏感植物的雌雄同体，再到部分乙烯不敏感植物的雌雄同株。发现雌性花转变的诱导与乙烯生物合成基因 CpACS11、CpACO2 和 CpACS27 的上调有关，这三个基因是雌性花发育所必需的。本文提出了一个模型，将乙烯生物合成和受体基因整合到调控南瓜性别决定的遗传网络中。
