小麦春化发育的分子调控机理研究进展

春化发育特性是小麦品种的重要性状,直接影响着小麦品种的种植范围和利用效率.本文就小麦春化相关基因的发现,以及对春化相关基因VRN1、VRN2和VRN3的克隆、表达特性以及春化发育分子调控机理方面的研究进展进行了综述.     

九个春化作用特性不同的小麦品种中VRN1基因的组成和特性分析

采用序列特异性PCR扩增技术,分析9个春化特性不同品种小麦春化基因VRN1在A、B和D基因组中等位基因的显隐性组成特性的结果表明:小麦品种'辽春15'中春化基因VRN1的A、B和D等位基因均为显性;小麦品种'新春2号'只在A基因组中为显性;小麦品种'豫麦18'的D基因组中为显性;'郑麦9023'和'新冬18'两个品种的B基因组中为显性;'周麦18'、'豫麦49-198'、'京841'和'肥麦'4个品种的A、B和D等位基因均为隐性.     

高羊茅春化基因FeVRN2的克隆及其在非生物胁迫下的表达

VRN2基因是受春化作用负调控的开花抑制子。为揭示非生物胁迫下高羊茅(Festuca elata)春化基因VRN2的分子调控机制,本研究以高羊茅为实验材料,采用c DNA末端快速扩增技术,克隆得到VRN2基因全长c DNA序列,命名为Fe VRN2。Fe VRN2基因c DNA全长为1 219 bp,具有一个完整的长度为657 bp的开放阅读框,编码蛋白质产物长度为218个氨基酸,并包含一个CCT保守结构域。同源性分析表明Fe VRN2与禾本科植物圆锥小麦(Triticum turgidum)、节节麦(Aegilops tauschii)、山羊草(Aegilops speltoides)、二穗短柄草(Brachypodium distachyon)、大麦(Hordeum vulgare subsp.vulgare)的亲缘关系非常近。荧光定量PCR结果显示:Fe VRN2基因在高羊茅叶片中的表达受高温、干旱与高盐胁迫特异诱导,说明该基因参与了高羊茅对高温、干旱与高盐胁迫的适应性调控。     

植物非编码RNA调控春化作用的表观遗传

在自然界中许多高等植物需要通过冬季的低温阶段实现从营养生长到生殖生长的时期转化,这一生物学过程称作春化作用。小麦(Triticum aestivum L.)和油菜(Brassica napus L.)等作物以种子为产品器官,生产上往往通过茬口安排和栽培措施使植株尽早通过春化作用,以促进花芽形成和花器官发育,而大白菜(B rapa ssp.pekinenesis)和甘蓝(B.oleracea)等作物以叶球等营养器官作为产品器官,生产上则设法避免低温引起的春化作用,以保证产品器官的充分生长。FLOWERING LOCUS C(FLC)作为一种重要的开花抑制蛋白负调控春化作用,参与植株从营养生长向生殖生长的转化过程。文章综述了春化中FLC表达受抑制主要通过低温诱导表达FLC基因区域的非编码RNA以及VRN1、VRN2、VIN3等蛋白参与介导组蛋白甲基化,从而在表观遗传上控制春化作用的进程和产品器官的正常发育。     

黄淮南片冬麦区主导品种春化基因及冬春性分析

以1950～2007年黄淮南片冬麦区的127个主导小麦品种为材料,利用第5同源群的春化基因分子标记对其进行了春化基因检测,并分析了小麦品种的春化基因与其冬春性的对应关系及黄淮南片冬麦区8次品种更换中春化基因与品种冬春性的演变规律.结果表明,参试品种中没有品种携带显性Vrn-A1基因,7个品种含有Vrn-B1基因(5.5%),2个品种含有Vrn-B1+Vrn-D1基因(1.6%),56个品种含有Vrn-D1基因(44.1%).春化基因类型与品种冬春特性基本相符,春化基因控制着小麦品种的冬春特性.主导品种含春化显性基因频率的变化趋势与冬春性变化规律存在较大差异,与传统方法相比,仅用春化基因来确定品种冬春性存在一定的不完善之处.采用春化基因分子标记与传统的冬春性鉴定方法相结合来认识品种冬春性、预测品种的抗寒性对黄淮南片冬麦区的小麦品种利用更具有指导意义.     

费尔干猪毛菜病程相关蛋白基因SfPR-1的表达规律和植物表达载体构建

采用RT-PCR技术探究盐生植物费尔干猪毛菜病程相关蛋白基因SfPR-1(GenBank登录号:JQ670917)在不同发育时期、组织部位、植物激素、非生物胁迫及生物胁迫处理下的表达规律,以揭示该基因在费尔干猪毛菜生长发育和逆境胁迫下的作用。结果表明,不同组织(根、茎、叶)中,SfPR-1在根中表达量最高,预示该基因可能在根防御中发挥主要作用;SfPR-1在不同发育阶段(种子、种子萌发20 d幼苗、种子萌发30 d幼苗、种子萌发40 d幼苗)的表达特性显示,种子萌发30 d幼苗时,其表达差异最显著,表明其可能在植株后期生长发育中具有重要作用;SfPR-1对不同植物激素(水杨酸SA、茉莉酸JA、脱落酸ABA、乙烯合成前体ACC)均产生了响应,表明该基因在几条主要的抗病防御通路中均发挥作用。非生物胁迫(H2O2、盐、旱、冷)都能够诱导SfPR-1基因的表达,其中对盐响应程度最高。以植源性意大利青霉(Penicillium italicum)进行生物胁迫时,SfPR-1表达呈持续上升趋势。以上结果表明费尔干猪毛菜病程相关蛋白基因SfPR-1是生物与非生物逆境胁迫下均响应的基因,推测其在植物抵御逆境胁迫中发挥重要作用。     

盐胁迫对互花米草种子萌发及胚生长的影响

以1/2Hoagland溶液为基础培养液,研究了1×104-6×104mg/L NaCl对互花米草(Spartina alterniflora)种子萌发的影响.结果表明,互花米草种子在萌发阶段胚芽鞘和胚轴生长先于胚根和胚芽;当盐浓度不超过3×104mg/L时,互花米草种子的萌发率未受到影响,种子萌发及胚生长的适宜盐浓度为1 x104mg/L,盐浓度对胚的不同部位生长的抑制程度不同,随着盐浓度的升高,胚根、胚芽的长度旱明显下降趋势,但盐浓度对胚轴、胚芽鞘生长的抑制作用较小,有利于已萌发的互花米草幼苗快速出土,迅速适应多变的潮间带环境.     

干旱胁迫对小麦幼苗根系生长和叶片光合作用的影响

采用水培试验方法,以2个耐旱性不同的小麦品种(敏感型望水白和耐旱型洛旱7号)为材料,研究了干旱胁迫对小麦幼苗根系形态、生理特性以及叶片光合作用的影响,以期揭示小麦幼苗对干旱胁迫的适应机制.结果表明： 干旱胁迫下,2个小麦品种幼苗的根系活力显著增大,而根数和根系表面积受到抑制;干旱胁迫降低了望水白的叶片相对含水量,提高了束缚水/自由水,而对洛旱7号无显著影响;干旱胁迫降低了2个小麦品种叶片的叶绿素含量、净光合速率、蒸腾速率、气孔导度和胞间CO2浓度,但随胁迫时间的延长,洛旱7号的叶绿素含量和净光合速率与对照差异不显著;干旱胁迫降低了2个小麦品种幼苗的单株叶面积,以及望水白的根系、地上部和植株生物量,而对洛旱7号无显著影响.水分胁迫下,耐旱型品种可以通过提高根系活力、保持较高的根系生长量来补偿根系吸收面积的下降,保持较高的根系吸水能力,进而维持较高的光合面积和光合速率,缓解干旱对生长的抑制.     

干旱胁迫对小麦幼苗根系生长和叶片光合作用的影响

采用水培试验方法,以2个耐旱性不同的小麦品种(敏感型望水白和耐旱型洛旱7号)为材料,研究了干旱胁迫对小麦幼苗根系形态、生理特性以及叶片光合作用的影响,以期揭示小麦幼苗对干旱胁迫的适应机制.结果表明： 干旱胁迫下,2个小麦品种幼苗的根系活力显著增大,而根数和根系表面积受到抑制;干旱胁迫降低了望水白的叶片相对含水量,提高了束缚水/自由水,而对洛旱7号无显著影响;干旱胁迫降低了2个小麦品种叶片的叶绿素含量、净光合速率、蒸腾速率、气孔导度和胞间CO2浓度,但随胁迫时间的延长,洛旱7号的叶绿素含量和净光合速率与对照差异不显著;干旱胁迫降低了2个小麦品种幼苗的单株叶面积,以及望水白的根系、地上部和植株生物量,而对洛旱7号无显著影响.水分胁迫下,耐旱型品种可以通过提高根系活力、保持较高的根系生长量来补偿根系吸收面积的下降,保持较高的根系吸水能力,进而维持较高的光合面积和光合速率,缓解干旱对生长的抑制.     

玉米AGO基因的克隆与表达分析

以玉米自交系‘昌7-2’三叶期前后2个时间点(种子萌发后5d和8d)幼苗不同组织部位的总RNA为研究对象,采用实时荧光定量PCR技术,对玉米中6个Argonaute(AGO)蛋白家族基因(AGO1、AGO2、AGO4、AGO5、AGO7和AGO10)在幼苗不同发育时期及不同组织部位的表达谱进行了研究。结果表明:(1)AGO1、AGO2、AGO4和AGO7在种子萌发后5d和8d幼苗不同组织中均有表达,种子萌发后5d幼苗中的平均表达量均高于萌发8d的幼苗,且在地上部分新生组织或细胞分裂比较旺盛的组织中表达较多,表明AGO1、AGO2、AGO4和AGO7可能在玉米幼苗发育早期的分生组织分裂生长中发挥调控作用。(2)AGO5和AGO10只在叶片和茎尖中表达,其他组织中不表达;其中AGO5主要集中在新生叶和种子萌发后8d的茎尖中,AGO10在玉米叶发育过程中可能存在着迁移的现象。     

Discrete developmental roles for temperate cereal grass VERNALIZATION1/FRUITFULL-like genes in flowering competency and the transition to flowering

Members of the grass subfamily Pooideae are characterized by their adaptation to cool temperate climates. Vernalization is the process whereby flowering is accelerated in response to a prolonged period of cold. Winter cereals are tolerant of low temperatures and flower earlier with vernalization, whereas spring cultivars are intolerant of low temperatures and flower later with vernalization. In the pooid grasses wheat (Triticum monococcum, Triticum aestivum) and barley (Hordeum vulgare), vernalization responsiveness is determined by allelic variation at the VERNALIZATION1 (VRN1) and/or VRN2 loci. To determine whether VRN1, and its paralog FRUITFULL2 (FUL2), are involved in vernalization requirement across Pooideae, we determined expression profiles for multiple cultivars of oat (Avena sativa) and wheat with and without cold treatment. Our results demonstrate significant up-regulation of VRN1 expression in leaves of winter oat and wheat in response to vernalization; no treatment effect was found for spring or facultative growth habit oat and wheat. Similar cold-dependent patterns of leaf expression were found for FUL2 in winter oat, but not winter wheat, suggesting a redundant qualitative role for these genes in the quantitative induction of flowering competency of oat. These and other data support the hypothesis that VRN1 is a common regulator of vernalization responsiveness within the crown pooids. Finally, we found that up-regulation of VRN1 in vegetative meristems of oat was significantly later than in leaves. This suggests distinct and conserved roles for temperate cereal grass VRN1/FUL-like genes, first, in systemic signaling to induce flowering competency, and second, in meristems to activate genes involved in the floral transition.     

Wheat SOC1 functions independently of WAP1/VRN1, an integrator of vernalization and photoperiod flowering promotion pathways

Heading time in bread wheat ( Triticum aestivum L.) is determined by three characters – vernalization requirement, photoperiodic sensitivity and narrow-sense earliness (earliness per se) – which are involved in the phase transition from vegetative to reproductive growth. The wheat APETALA1 ( AP1 )-like MADS-box gene, wheat AP1 ( WAP1 , identical with VRN1 ), has been identified as an integrator of vernalization and photoperiod flowering promotion pathways. A MADS-box gene, SUPPRESSOR OF OVEREXPRESSION OF CO 1 ( SOC1 ) is an integrator of flowering pathways in Arabidopsis . In this study, we isolated a wheat ortholog of SOC1 , wheat SOC1 ( WSOC1 ), and investigated its relationship to WAP1 in the flowering pathway. WSOC1 is expressed in young spikes but preferentially expressed in leaves. Expression starts before the phase transition and is maintained during the reproductive growth phase. Overexpression of WSOC1 in transgenic Arabidopsis plants caused early flowering under short-day conditions, suggesting that WSOC1 functions as a flowering activator in Arabidopsis . WSOC1 expression is affected neither by vernalization nor photoperiod, whereas it is induced by gibberellin at the seedling stage. Furthermore, WSOC1 is expressed in transgenic wheat plants in which WAP1 expression is cosuppressed. These findings indicate that WSOC1 acts in a pathway different from the WAP1 -related vernalization and photoperiod pathways.     

The molecular basis of vernalization-induced flowering in cereals

Genetic analyses have identified three genes that control the vernalization requirement in wheat and barley; VRN1, VRN2 and FT (VRN3). These genes have now been isolated and shown to regulate not only the vernalization response but also the promotion of flowering by long days. VRN1 is induced by vernalization and accelerates the transition to reproductive development at the shoot apex. FT is induced by long days and further accelerates reproductive apex development. VRN2, a floral repressor, integrates vernalization and day-length responses by repressing FT until plants are vernalized. A comparison of flowering time pathways in cereals and Arabidopsis shows that the vernalization response is controlled by different MADS box genes, but integration of vernalization and long-day responses occurs through similar mechanisms.     

The quantitative response of wheat vernalization to environmental variables indicates that vernalization is not a response to cold temperature

The initiation of flowering is a crucial trait that allows temperate plants to flower in the favourable conditions of spring. The timing of flowering initiation is governed by two main mechanisms: vernalization that defines a plant's requirement for a prolonged exposure to cold temperatures; and photoperiod sensitivity defining the need for long days to initiate floral transition. Genetic variability in both vernalization and photoperiod sensitivity largely explains the adaptability of cultivated crop plants such as bread wheat (Triticum aestivum L.) to a wide range of climatic conditions. The major genes controlling wheat vernalization (VRN1, VRN2, and VRN3) and photoperiod sensitivity (PPD1) have been identified, and knowledge of their interactions at the molecular level is growing. However, the quantitative effects of temperature and photoperiod on these genes remain poorly understood. Here it is shown that the distinction between the temperature effects on organ appearance rate and on vernalization sensu stricto is crucial for understanding the quantitative effects of the environmental signal on wheat flowering. By submitting near isogenic lines of wheat differing in their allelic composition at the VRN1 locus to various temperature and photoperiod treatments, it is shown that, at the whole-plant level, the vernalization process has a positive response to temperature with complex interactions with photoperiod. In addition, the phenotypic variation associated with the presence of different spring homoeoalleles of VRN1 is not induced by a residual vernalization requirement. The results demonstrate that a precise definition of vernalization is necessary to understand and model temperature and photoperiod effects on wheat flowering. It is suggested that this definition should be used as the basis for gene expression studies and assessment of functioning of the wheat flowering gene network, including an explicit account of the quantitative effect of environmental variables.     

Effect of Ppd-1 on the expression of flowering-time genes in vegetative and reproductive growth stages of wheat

The photoperiod sensitivity gene Ppd-1 influences the timing of flowering in temperate cereals such as wheat and barley. The effect of Ppd-1 on the expression of flowering-time genes was assessed by examining the expression levels of the vernalization genes VRN1 and VRN3/WFT and of two CONSTANS-like genes, WCO1 and TaHd1, during vegetative and reproductive growth stages. Two near-isogenic lines (NILs) were used: the first carried a photoperiod-insensitive allele of Ppd-1 (Ppd-1a-NIL), the other, a photoperiod-sensitive allele (Ppd-1b-NIL). We found that the expression pattern of VRN1 was similar in Ppd-1a-NIL and Ppd-1b-NIL plants, suggesting that VRN1 is not regulated by Ppd-1. Under long day conditions, VRN3/WFT showed similar expression patterns in Ppd-1a-NIL and Ppd-1b-NIL plants. However, expression differed greatly under short day conditions: VRN3/WFT expression was detected in Ppd-1a-NIL plants at the 5-leaf stage when they transited from vegetative to reproductive growth; very low expression was present in Ppd-1b-NIL throughout all growth stages. Thus, the Ppd-1b allele acts to down-regulate VRN3/WFT under short day conditions. WCO1 showed high levels of expression at the vegetative stage, which decreased during the phase transition and reproductive growth stages in both Ppd-1a-NIL and Ppd-1b-NIL plants under short day conditions. By contrast to WCO1, TaHd1 was up-regulated during the reproductive stage. The level of TaHd1 expression was much higher in Ppd-1a-NIL than the Ppd-1b-NIL plants, suggesting that the Ppd-1b allele down-regulates TaHd1 under short day conditions. The present study indicates that down-regulation of VRN3/WFT together with TaHd1 is the cause of late flowering in the Ppd-1b-NIL plants under short day conditions.     

Cloning and characterization of SOC1 homologs in barley (Hordeum vulgare) and their expression during seed development and in response to vernalization

A number of genes are involved in the vernalization pathway, such as VRN1, VRN2 and VRN3/FT1, whose function has been studied in barley and wheat. However, the function of the flowering and vernalization integrator SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) has not been well studied in Triticeae, and particularly in barley. Herein, we cloned and characterized two barley SOC1-like homologs, HvSOC1-like1 and HvSOC1-like2. Primary sequence analysis of the predicted HvSOC1-like1 and HvSOC1-like2 proteins showed that they are members of the type II MADS-box protein family. Phylogenetic analysis placed the predicted proteins with other SOC1 and SOC1-like proteins from different species neighboring those from other cereal plant species. Primary and secondary structures of the predicted proteins are conserved to each other and more distant to the recently identified barley ODDSOC1 proteins. Genomic organization of HvSOC1-like1 is very similar to the Arabidopsis and Brachypodium SOC1 genes and localized in highly syntenic chromosomal regions. Regulatory cis-acting elements detected in the HvSOC1-like1 promoter include the CArG-box, implicated in the regulation of SOC1 expression in Arabidopsis. Both HvSOC1-like1 and HvSOCI-like2 are expressed in vegetative and reproductive tissues and at different stages of seed development. Both are upregulated in a particular seed developmental stage suggesting their possible implication in seed development. Furthermore, HvSOC1-like1 was induced in two winter barley cultivars after vernalization treatment pointing to its probable involvement in the vernalization process. The study of the SOC1 genes reported here opens the way for a better understanding of both the vernalization process and seed development and germination in this important cereal crop.