Homeotic sexual translocations and the origin of maize (Zea mays, Poaceae):: A new look at an old problem
Homeotic sexual translocations and the origin of maize (Zea mays, Poaceae):: A new look at an old problem
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DOI：
10.1007/bf02866598
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发表时间：
2000-01-01
期刊：
影响因子：
2.6
通讯作者：
Iltis, HH
中科院分区：
文献类型：
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作者：
Iltis, HH
在玉米争议的起源，即正统类蜀黍假说（OTH；Beadle 1939，1972；Iltis 1971）中，五个关键突变将类蜀黍（野生玉米）每列有单排谷粒的 2 列（二列）穗改变为每列有双列谷粒的 4 到多列（多列）玉米穗。但是类蜀黍穗位于玉米穗 I 度分支轴的侧面，就像它们的雄性同源物一样，类蜀黍 I 度分支穗穗刺，末端，这是一个长期未被识别的谜，因此被忽略。在现已废弃的灾难性性嬗变理论（CSTT；Iltis 1983b，1987）中，类蜀黍的 I 度分支雄穗（雄性）（小穗软穗，成对，即每列双行，如玉米穗），当通过分支凝结而受到雌性激素控制时，就会女性化为玉米原穗。但是侧耳应该保持类蜀黍类（2级，每级有单排谷物），但实际上是双排的。结合OTH和CSTT，新的性易位理论（STLT）基于：首先是类蜀黍耳簇的分支模式（Camara-H.＆Gambino 1990），依次成熟，对称分支，典型的Andropogonoid系统，称为rhipidia （唱。rhipidium），每个较高级（较年轻）的穗起源于其较低级、较早成熟的前身的侧枝；其次，在 3 或 4 个关键突变上（壳杯减少、颖片软化、雌性小穗加倍），这些突变通过向外突出谷物，使它们易于接近，从而吸引了人类的驯化。在每个耳簇内，将选择最早成熟的、因此营养垄断且最大的耳朵，所有年轻的耳朵已经受到营养抑制，受到抑制。随着数量更少、更大的耳朵进化出来，分支节间凝结将雄性雄缨移动到雌性荷尔蒙区域，同源异型转换将雌性形态转移到末端雄性位置：首先用耳朵（雌性）取代每个 II 度分支雄缨，最终取代 I 度分支缨（雄性）。有了这个，现在雌性结构在顶端占主导地位，因此最需要营养的末端位置逐渐抑制其下方I度分支上的所有附属穗，多穗突变（取决于营养超载）最终被允许表达，并且多行玉米穗（最初具有返祖雄性轨道）进化。受人类选择的青睐，逐步同源异型性转变导致顶端优势的增加解释了考古学和形态学的现实，但需要与发育遗传学的最新结果相协调。目前的证据表明，大蜀黍最初是因为其绿色的耳朵和含糖的髓而被狩猎采集者作为远离其故乡的小“花园”种群的偶尔雨季食物，而不是因为其富含谷物的坚硬果皮，它们很容易被大量收集，但作为食物却毫无用处，迄今为止，考古记录中尚不清楚。一种罕见的释放谷物的类蜀黍突变体（可能仅在一种“创始”植物中表达，即一种长形植物“夏娃”），它暴露了包裹的谷物以便于收获，很快就被认为是有用的，被收集和种植（或自行种植）。因此，玉米开始了独特的园艺驯化之路，这是温带旧大陆大规模选择的农业谷物无法比拟的。
In the Origin of Maize Controversy, the Orthodox Teosinte Hypothesis (OTH; Beadle 1939, 1972; Iltis 1971), five key mutations change 2-ranked (distichous) ears of teosinte (wild Zea) with a single row of grains per rank to 4- to many-ranked (polystichous) maize ears with a double row of grains per rank. BUT teosinte ears are lateral to the I degrees branch axes maize ears, like their male homologues, the teosinte I degrees branch tassel spikes, terminal, an enigma long unrecognized, hence ignored. In the Catastrophic Sexual Transmutation Theory (CSTT; Iltis 1983b, 1987), now abandoned, the I degrees branch tassel (male) of teosinte (spikelets soft-glumed, paired, i.e., double-rowed per rank, as in maize ears), when brought under female hormonal control by branch condensation becomes feminized into a maize proto-ear. BUT lateral ears should then have remained teosintoid (2-ranked, each rank with a single row of grains), yet are in fact double-rowedCombining OTH and CSTT, the new Sexual Translocation Theory (STLT) is based on: first the branching pattern of teosinte ear clusters (Camara-H. & Gambino 1990), sequentially maturing, sympodially branching, typically Andropogonoid systems, called rhipidia (sing. rhipidium), where each higher order (younger) ear originates as a lateral branch of its lower order, earlier maturing predecessor; and second, on 3 or 4 key mutations [cupule reduction, softening of glumes, doubling of female spikelets], which, by projecting outward the grains invited human domestication by making them accessible. Within each ear cluster the earliest maturing, hence nutrient-monopolizing and largest ear would be selected, all younger ears, already nutrient-inhibited, suppressed. As fewer, larger ears evolved, and branch internode condensation moved male tassels into female hormonal zones, homeotic conversions translocated female morphology to terminal male positions: first replacing each of the II degrees branch tassels, and ultimately the I degrees branch tassel (male), with an ear (female). With this, now female structure in the apically dominant, hence most nutrient-demanding terminal position gradually suppressing all subsidiary ears on the I degrees branch beneath it, mutations for polystichy (contingent on nutrient overload) were finally allowed to become expressed, and the multi-rowed maize ear (at first with an atavistic male rail) evolved. Favored by human selection, these increases in apical dominance by stepwise homeotic sexual conversions explain both archeological and morphological realities, but need to be harmonized with recent results of developmental genetics.Current evidence suggests that teosinte was first tended for its green ears and sugary pith by hunter-gatherers as an occasional rainy-season food in small "garden" populations away from its homeland and not for its abundant grain-containing, hard fruitcases, which easily mass-collected but useless as food, are as yet unknown from the archeological record. A rare grain-liberating teosinte mutation (probably expressed in only one "founder" plant, a mazoid "Eve"), which exposed the encased grain for easy harvest, was soon recognized as useful, collected and planted (or self-planted). Thus maize was started an its way to a unique horticultural domestication that is not comparable to that of the temperate Old World mass-selected agricultural grains.