The New Zealand Institute for Plant & Food Research, Private Bag 4604, Christchurch, New Zealand.
Ann Bot. 2013 Dec;112(9):1683-703. doi: 10.1093/aob/mct224. Epub 2013 Nov 11.
A model to predict anthesis time of a wheat plant from environmental and genetic information requires integration of current concepts in physiological and molecular biology. This paper describes the structure of an integrated model and quantifies its response mechanisms.
Literature was reviewed to formulate the components of the model. Detailed re-analysis of physiological observations are utilized from a previous publication by the second two authors. In this approach measurements of leaf number and leaf and primordia appearance of near isogenic lines of spring and winter wheat grown for different durations in different temperature and photoperiod conditions are used to quantify mechanisms and parameters to predict time of anthesis.
The model predicts the time of anthesis from the length of sequential phases: 1, embryo development; 2, dormant; 3, imbibed/emerging; 4, vegetative; 5, early reproductive; 6, pseudo-stem extension; and 7, ear development. Phase 4 ends with vernalization saturation (VS), Phase 5 with terminal spikelet (TS) and Phase 6 with flag leaf ligule appearance (FL). The durations of Phases 4 and 5 are linked to the expression of Vrn genes and are calculated in relation to change in Haun stage (HS) to account for the effects of temperature per se. Vrn1 must be expressed to sufficient levels for VS to occur. Vrn1 expression occurs at a base rate of 0·08/HS in winter 'Batten' and 0·17/HS in spring 'Batten' during Phases 1, 3 and 4. Low temperatures promote expression of Vrn1 and accelerate progress toward VS. Our hypothesis is that a repressor, Vrn4, must first be downregulated for this to occur. Rates of Vrn4 downregulation and Vrn1 upregulation have the same exponential response to temperature, but Vrn4 is quickly upregulated again at high temperatures, meaning short exposure to low temperature has no impact on the time of VS. VS occurs when Vrn1 reaches a relative expression of 0·76 and Vrn3 expression begins. However, Vrn2 represses Vrn3 expression so Vrn1 must be further upregulated to repress Vrn2 and enable Vrn3 expression. As a result, the target for Vrn1 to trigger VS was 0·76 in 8-h photoperiods (Pp) and increased at 0·026/HS under 16-h Pp as levels of Vrn2 increased. This provides a mechanism to model short-day vernalization. Vrn3 is expressed in Phase 5 (following VS), and apparent rates of Vrn3 expression increased from 0·15/HS at 8-h Pp to 0·33/HS at 16-h Pp. The final number of leaves is calculated as a function of the HS at which TS occurred (TS(HS)): 2·86 + 1·1 × TS(HS). The duration of Phase 6 is then dependent on the number of leaves left to emerge and how quickly they emerge.
The analysis integrates molecular biology and crop physiology concepts into a model framework that links different developmental genes to quantitative predictions of wheat anthesis time in different field situations.
需要整合生理和分子生物学的现有概念，才能从环境和遗传信息中预测小麦植物的开花时间。本文描述了一个综合模型的结构，并量化了其响应机制。
通过回顾文献来构建模型的组成部分。第二个和第三个作者之前的一篇出版物中详细重新分析了生理观察结果。在这种方法中，使用了不同春小麦和冬小麦近等基因系在不同温度和光周期条件下生长不同时间的叶片数和叶片及原基出现的测量值，以量化预测开花时间的机制和参数。
该模型根据以下顺序阶段的长度预测开花时间：1，胚胎发育；2，休眠；3，吸水/萌发；4，营养生长；5，早期生殖；6，假茎延伸；7，穗部发育。第 4 阶段以春化饱和（VS）结束，第 5 阶段以终穗（TS）结束，第 6 阶段以旗叶叶舌出现（FL）结束。第 4 阶段和第 5 阶段的持续时间与 Vrn 基因的表达有关，并与 Haun 阶段（HS）的变化相关联，以解释温度本身的影响。必须表达 Vrn1 才能达到 VS。在第 1、3 和 4 阶段，冬小麦“Batten”中的 Vrn1 以 0·08/HS 的基础速率表达，而春小麦“Batten”中的 Vrn1 以 0·17/HS 的基础速率表达。低温促进 Vrn1 的表达并加速向 VS 推进。我们的假设是，首先必须下调 Vrn4 抑制剂。Vrn4 下调和 Vrn1 上调的速率对温度具有相同的指数响应，但 Vrn4 在高温下很快再次上调，这意味着低温暴露时间对 VS 时间没有影响。当 Vrn1 达到相对表达水平 0·76 并开始表达 Vrn3 时，VS 发生。然而，Vrn2 抑制 Vrn3 的表达，因此 Vrn1 必须进一步上调以抑制 Vrn2 并使 Vrn3 表达。因此，Vrn1 触发 VS 的目标是在 8-h 光周期（Pp）下为 0·76，并随着 Vrn2 水平的增加，在 16-h Pp 下增加到 0·026/HS。这为模型化短日春化提供了一种机制。Vrn3 在第 5 阶段（VS 之后）表达，Vrn3 表达的表观速率从 8-h Pp 下的 0·15/HS 增加到 16-h Pp 下的 0·33/HS。最后叶片数的计算是作为 TS 发生时的 HS（TS(HS)）的函数：2·86 + 1·1 × TS(HS)。然后，第 6 阶段的持续时间取决于出现的叶片数量以及它们出现的速度。
该分析将分子生物学和作物生理学概念整合到一个模型框架中，该框架将不同的发育基因与不同田间条件下小麦开花时间的定量预测联系起来。
