Department of Genetics and Plant Production, Aula Dei Experimental Station, EEAD-CSIC, Avda. Montañana 1005, Zaragoza, Spain.
BMC Plant Biol. 2011 Nov 18;11:164. doi: 10.1186/1471-2229-11-164.
Understanding the adaptation of cereals to environmental conditions is one of the key areas in which plant science can contribute to tackling challenges presented by climate change. Temperature and day length are the main environmental regulators of flowering and drivers of adaptation in temperate cereals. The major genes that control flowering time in barley in response to environmental cues are VRNH1, VRNH2, VRNH3, PPDH1, and PPDH2 (candidate gene HvFT3). These genes from the vernalization and photoperiod pathways show complex interactions to promote flowering that are still not understood fully. In particular, PPDH2 function is assumed to be limited to the ability of a short photoperiod to promote flowering. Evidence from the fields of biodiversity, ecogeography, agronomy, and molecular genetics was combined to obtain a more complete overview of the potential role of PPDH2 in environmental adaptation in barley.
The dominant PPDH2 allele is represented widely in spring barley cultivars but is found only occasionally in modern winter cultivars that have strong vernalization requirements. However, old landraces from the Iberian Peninsula, which also have a vernalization requirement, possess this allele at a much higher frequency than modern winter barley cultivars. Under field conditions in which the vernalization requirement of winter cultivars is not satisfied, the dominant PPDH2 allele promotes flowering, even under increasing photoperiods above 12 h. This hypothesis was supported by expression analysis of vernalization-responsive genotypes. When the dominant allele of PPDH2 was expressed, this was associated with enhanced levels of VRNH1 and VRNH3 expression. Expression of these two genes is needed for the induction of flowering. Therefore, both in the field and under controlled conditions, PPDH2 has an effect of promotion of flowering.
The dominant, ancestral, allele of PPDH2 is prevalent in southern European barley germplasm. The presence of the dominant allele is associated with early expression of VRNH1 and early flowering. We propose that PPDH2 promotes flowering of winter cultivars under all non-inductive conditions, i.e. under short days or long days in plants that have not satisfied their vernalization requirement. This mechanism is indicated to be a component of an adaptation syndrome of barley to Mediterranean conditions.
了解谷类作物对环境条件的适应是植物科学能够应对气候变化所带来的挑战的关键领域之一。温度和日照长度是控制温带谷类作物开花和适应的主要环境调节剂。控制大麦对环境信号响应开花时间的主要基因有 VRNH1、VRNH2、VRNH3、PPDH1 和 PPDH2（候选基因 HvFT3）。这些来自春化和光周期途径的基因表现出复杂的相互作用，以促进开花，但仍未被完全理解。特别是，PPDH2 的功能被认为仅限于短日照促进开花的能力。从生物多样性、生态地理学、农学和分子遗传学等领域收集的证据，综合起来可以更全面地了解 PPDH2 在大麦环境适应中的潜在作用。
主导的 PPDH2 等位基因在春大麦品种中广泛存在，但在现代冬季品种中很少发现，现代冬季品种对春化有很强的要求。然而，来自伊比利亚半岛的古老地方品种也有春化要求，其等位基因的频率比现代冬季大麦品种高得多。在冬季品种的春化要求得不到满足的田间条件下，主导的 PPDH2 等位基因促进开花，即使在 12 小时以上的日照长度增加的情况下也是如此。这一假设得到了春化反应基因型表达分析的支持。当 PPDH2 的主导等位基因表达时，与 VRNH1 和 VRNH3 表达水平的增强相关。这两个基因的表达是诱导开花所必需的。因此，无论是在田间还是在受控条件下，PPDH2 都具有促进开花的作用。
PPDH2 的主导、祖先等位基因在南欧大麦种质资源中普遍存在。主导等位基因的存在与 VRNH1 和早期开花的早期表达相关。我们提出，PPDH2 促进所有非诱导条件下的冬季品种开花，即在未满足春化要求的短日或长日条件下的植物中。这一机制是大麦适应地中海条件的适应综合征的一个组成部分。
