拟南芥低磷胁迫反应分子机理研究的最新进展

本文综述了拟南芥低磷(Pi)胁迫反应分子机理的最新研究进展,重点介绍了低磷胁迫反应中的SUMOylation途径、转录因子在低磷反应中的功能、Pi平衡调节机制以及磷脂酶在Pi的循环利用过程中的作用,总结了已经鉴定的参与低磷胁迫反应的基因及其可能存在的相互关系。     

磷饥饿对番茄幼苗H+分泌及Pi吸收的影响

磷饥饿条件下番茄幼苗的H⁺分泌速率明显提高。质膜质子泵专一性抑制剂钒酸盐能显著抑制番茄幼苗的H⁺分泌,也能显著抑制其Pi吸收。此结果表明,磷饥饿时番茄幼苗Pi吸收速率的变化与H⁺分泌速率的变化之间可能具有一定的相关性,并进一步暗示质膜H⁺-ATPase可能参与其中。本文结果还表明,Pi/H⁺的准量关系约为1:1。     

植物的磷营养：磷酸盐运转系统及其调节

对近年来植物磷营养中有关Pi运转系统及其调节等方面的研究进展进行简要介绍,并对今后有关的研究趋势作了初步展望。     

磷缓解水鳖镉毒害的生理研究

研究了Cd对水鳖生理生化过程的影响及Pi对Cd胁迫的缓解作用。结果显示,Cd能抑制水鳖的代谢和生长,使叶绿素含量与光合速率下降,呼吸速率与可溶性糖含量增加,POD活性增强;当加入0.6mmol/L Pi后,能相对减轻Cd造成的毒害,表现出Pi对Cd的拮抗和缓解作用。     

低磷胁迫下不同种源马尾松的根构型与磷效率

以浙江淳安、福建武平、广西岑溪和广东信宜4个代表性的马尾松种源为试材,设置异质低磷胁迫、同质低磷胁迫等不同磷素处理,研究马尾松种源感知不同类型低磷胁迫的根构型及磷效率变异规律.结果表明:无论在异质低磷还是同质低磷胁迫下,参试种源马尾松的主要生长性状和磷效率指标均存在极显著的种源间变异.异质低磷胁迫下,广东信宜、福建武平种源马尾松表现出较高的磷效率和干物质积累量,根构型发生适应性变化,富磷表层介质中的根系参数显著高于低磷效率的广西岑溪和浙江淳安种源.这是磷高效种源具有较高的磷素吸收效率和磷效率的重要机制.不同种源的表层富磷介质根系参数与其整株干物质积累量相关系数在0.95以上.同质低磷胁迫下,高磷效率种源马尾松的磷吸收率显著高于低磷效率种源,但表层介质中的根系参数和整株根系参数与整株干物质积累量的相关性较低.不同种源马尾松适应同质低磷胁迫和异质低磷胁迫的生物学机制有所差异,应有针对性地选择不同土壤磷素的森林立地并推广磷营养高效的马尾松种源.     

玉米耐受低磷胁迫的分子机制研究进展

玉米是我国重要的粮食、饲料及生物能源作物,低磷胁迫严重影响其品质和产量。近年来,随着高通量测序技术的成熟及组学的发展,关于玉米耐受低磷胁迫的分子机制研究取得了一定进展。主要从玉米耐受磷胁迫相关基因的发掘、组学在研究玉米耐受低磷胁迫中的应用及QTL定位3个方面对玉米耐受低磷胁迫分子机制的研究进展进行了综述,以期为筛选、培育磷高效玉米种质提供理论参考。     

蔗糖添加对杉木低磷胁迫响应和蔗糖代谢的影响

为了揭示低磷胁迫下蔗糖对杉木低磷胁迫响应和蔗糖代谢的影响,选用两种不同磷效率杉木家系M32和M28进行低磷胁迫下的蔗糖添加试验,分析蔗糖添加对低磷胁迫下杉木形态特征、生理特性和低磷诱导相关基因表达的影响。结果表明：蔗糖添加促进了低磷胁迫下杉木苗高、根长、根表面积、根平均直径、根体积、根叶组织蔗糖含量和根叶组织无机磷含量的增加,但仍明显低于正常供磷处理下添加蔗糖处理的杉木增量。低磷促进杉木叶中花青素的积累,而正常供磷和低磷胁迫下的蔗糖添加处理都显著促进了叶片花青素含量的增加。随着胁迫时间的延长,M28与M32在根、叶组织的蔗糖含量存在显著差异,且M28根叶组织中的蔗糖合成酶活性和蔗糖磷酸合成酶活性都高于M32。蔗糖合成酶ClSuSy在M28和M32根系中受低磷胁迫诱导下调表达,但蔗糖添加处理明显诱导ClSuSy表达量升高,M28在正常供磷并添加蔗糖处理下的ClSuSy表达量显著高于其它处理。蔗糖转运蛋白SUT4、磷转运蛋白ClPht1;4、紫色酸性磷酸酶PAP1和PAP11在M28和M32根系中总体上受低磷胁迫诱导上调表达,且受蔗糖添加处理诱导下调表达。低磷胁迫下,添加或不添加蔗糖处理的M32根系SUT4的表达量均在15d时显著升高,并在45d时回落到正常水平。ClPht1;4和PAP1在低磷胁迫15d的表达量显著高于45d时的表达量,且ClPht1;4在M32根系中的表达量远高于M28。本研究表明,蔗糖对杉木低磷胁迫响应和糖代谢有重要的影响作用,低磷胁迫下添加蔗糖处理能够在一定程度上缓解杉木低磷胁迫响应。     

利用抑制性扣除杂交技术克隆水稻磷饥饿诱导基因

磷素是植物生长所必需的重要元素.在缺磷环境中,植物能够调节自身的形态、生理生化和基因表达水平来适应环境的变化.为研究水稻(Oryza sativa L.)耐低磷胁迫的分子机理,采用抑制性扣除杂交技术(SSH)构建磷饥饿诱导的水稻根系扣除cDNA文库.通过文库筛选和测序获得18个已知基因和47个功能未知基因.这些基因参与了不同的代谢过程,包括磷吸收和转运、信号传导、蛋白质合成和降解、碳水化合物代谢和胁迫反应.Northern杂交结果表明,在磷饥饿胁迫下这些基因呈现不同的表达模式,并且不同代谢过程中的基因对磷饥饿有着不同的反应.     

拟南芥SPL1基因参与调节低磷条件下的根际酸化反应

根际酸化是植物适应低磷胁迫的重要策略, 但植物是如何感知和转导低磷信号, 进而促进根际酸化的分子机制至今还不十分清楚。利用pH指示剂(溴甲酚紫)显色法从拟南芥(Arabidopsis thaliana) T-DNA插入突变体库中分离得到了1株低磷诱导根际酸化缺失突变体spl1。在含溴甲酚紫的低磷培养基上培养8小时, 野生型拟南芥根际培养基的颜色变为黄色, 而突变体spl1根际培养基的颜色没有明显变化, 表明spl1的低磷根际酸化反应能力降低。当低磷胁迫处理延长20天, spl1叶片的花青素积累明显高于野生型。同时也出现, 即使在磷营养正常条件下, spl1突变体也表现出根毛数量与长度增加的特征。进一步的研究表明, 在低磷条件下, spl1突变体根部的磷含量略高于野生型, 与磷转运相关基因的表达量明显高于野生型。分子遗传学分析结果表明, SPL1基因受低磷胁迫诱导, 主要在拟南芥的叶片和花等组织中表达, 其编码的蛋白广泛分布在细胞的各个部位。以上结果表明, SPL1参与介导低磷诱导的拟南芥根际酸化反应, 调节多种低磷胁迫反应及低磷条件下磷饥饿诱导基因的表达。     

植物miRNA在调节低磷胁迫响应中的作用

植物MicroRNA(miRNA)是一类内源性非编码小分子RNA,它们参与调节植物的生长、发育和代谢过程中多种基因的表达。近期的研究发现miRNA参与调节磷的吸收和利用,对植物适应低磷胁迫具有重要作用。本文概述了植物磷吸收和转运的机制,介绍了低磷胁迫下miRNA的表达水平变化,重点对miRNA在植物响应低磷胁迫中的作用,如改变根系结构、提高磷的转运和再利用效率、参与花青素和抗氧化物生物合成等进行了综述,以期为揭示植物低磷胁迫响应分子机制,提高植物对磷的吸收效率提供借鉴。     

The Pht1;9 and Pht1;8 transporters mediate inorganic phosphate acquisition by the Arabidopsis thaliana root during phosphorus starvation

? The activation of high-affinity root transport systems is the best-conserved strategy employed by plants to cope with low inorganic phosphate (Pi) availability, a role traditionally assigned to Pi transporters of the Pht1 family, whose respective contributions to Pi acquisition remain unclear. ? To characterize the Arabidopsis thaliana Pht1;9 transporter, we combined heterologous functional expression in yeast with expression/subcellular localization studies and reverse genetics approaches in planta. Double Pht1;9/Pht1;8 silencing lines were also generated to gain insight into the role of the closest Pht1;9 homolog. ? Pht1;9 encodes a functional plasma membrane-localized transporter that mediates high-affinity Pi/H? symport activity in yeast and is highly induced in Pi-starved Arabidopsis roots. Null pht1;9 alleles exhibit exacerbated responses to prolonged Pi limitation and enhanced tolerance to arsenate exposure, whereas Pht1;9 overexpression induces the opposite phenotypes. Strikingly, Pht1;9/Pht1;8 silencing lines display more pronounced defects than the pht1;9 mutants. ? Pi and arsenic plant content analyses confirmed a role of Pht1;9 in Pi acquisition during Pi starvation and arsenate uptake at the root-soil interface. Although not affecting plant internal Pi repartition, Pht1;9 activity influences the overall Arabidopsis Pi status. Finally, our results indicate that both the Pht1;9 and Pht1;8 transporters function in sustaining plant Pi supply on environmental Pi depletion.     

Phosphate sensing in higher plants

Phosphate (Pi) plays a central role as reactant and effector molecule in plant cell metabolism. However, Pi is the least accessible macronutrient in many ecosystems and its low availability often limits plant growth. Plants have evolved an array of molecular and morphological adaptations to cope with Pi limitation, which include dramatic changes in gene expression and root development to facilitate Pi acquisition and recycling. Although physiological responses to Pi starvation have been increasingly studied and understood, the initial molecular events that monitor and transmit information on external and internal Pi status remain to be elucidated in plants. This review summarizes molecular and developmental Pi starvation responses of higher plants and the evidence for coordinated regulation of gene expression, followed by a discussion of the potential involvement of plant hormones in Pi sensing and of molecular genetic approaches to elucidate plant signalling of low Pi availability. Complementary genetic strategies in Arabidopsis thaliana have been developed that are expected to identify components of plant signal transduction pathways involved in Pi sensing. Innovative screening methods utilize reporter gene constructs, conditional growth on organophosphates and the inhibitory properties of the Pi analogue phosphite, which hold the promise for significant advances in our understanding of the complex mechanisms by which plants regulate Pi-starvation responses.     

LEAF TIP NECROSIS1 plays a pivotal role in the regulation of multiple phosphate starvation responses in rice

Although phosphate (Pi) starvation signaling is well studied in Arabidopsis (Arabidopsis thaliana), it is still largely unknown in rice (Oryza sativa). In this work, a rice leaf tip necrosis1 (ltn1) mutant was identified and characterized. Map-based cloning identified LTN1 as LOC_Os05g48390, the putative ortholog of Arabidopsis PHO2, which plays important roles in Pi starvation signaling. Analysis of transgenic plants harboring a LTN1 promoter::β-glucuronidase construct revealed that LTN1 was preferentially expressed in vascular tissues. The ltn1 mutant exhibited increased Pi uptake and translocation, which led to Pi overaccumulation in shoots. In association with enhanced Pi uptake and transport, some Pi transporters were up-regulated in the ltn1 mutant in the presence of sufficient Pi. Furthermore, the elongation of primary and adventitious roots was enhanced in the ltn1 mutant under Pi starvation, suggesting that LTN1 is involved in Pi-dependent root architecture alteration. Under Pi-sufficient conditions, typical Pi starvation responses such as stimulation of phosphatase and RNase activities, lipid composition alteration, nitrogen assimilation repression, and increased metal uptake were also activated in ltn1. Moreover, analysis of OsmiR399-overexpressing plants showed that LTN1 was down-regulated by OsmiR399. Our results strongly indicate that LTN1 is a crucial Pi starvation signaling component downstream of miR399 involved in the regulation of multiple Pi starvation responses in rice.     

A miRNA involved in phosphate-starvation response in Arabidopsis

Although microRNAs (miRNAs) have been documented to regulate development in plants and animals , the function of miRNAs in physiology is unclear. miR399 has multiple target sites in the 5' untranslated region (UTR) of a gene encoding a putative ubiquitin-conjugating enzyme (UBC) in Arabidopsis thaliana. We report here that miR399 was highly induced, whereas the target UBC mRNA was reduced by low-phosphate (Pi) stress. In transgenic plants with constitutive expression of miR399, UBC mRNA accumulation was suppressed even under high Pi. The expression of transgene UBC mRNA with 5' UTR miR399 target sites, but not the one without 5' UTR, was reduced under low-Pi condition. Furthermore, transgenic Arabidopsis plants with constitutive expression of miR399 accumulated more Pi than the wild-type, and transgenic plants expressing the UBC mRNA without 5' UTR (miRNA-deregulated) showed less inhibition of primary root growth and less induction of a Pi transporter gene by low-Pi stress than those of wild-type plants. We conclude that miR399 downregulates UBC mRNA accumulation by targeting the 5' UTR, and this regulation is important for plant responses to Pi starvation. The results suggest that miRNAs have functional roles for plants to cope with fluctuations in mineral-nutrient availability in the soil.     

HPS4/SABRE regulates plant responses to phosphate starvation through antagonistic interaction with ethylene signalling

The phytohormone ethylene plays important roles in regulating plant responses to phosphate (Pi) starvation. To date, however, no molecular components have been identified that interact with ethylene signalling in regulating such responses. In this work, an Arabidopsis mutant, hps4, was characterized that exhibits enhanced responses to Pi starvation, including increased inhibition of primary root growth, enhanced expression of Pi starvation-induced genes, and overproduction of root-associated acid phosphatases. Molecular cloning indicated that hps4 is a new allele of SABRE, which was previously identified as an important regulator of cell expansion in Arabidopsis. HPS4/SABRE antagonistically interacts with ethylene signalling to regulate plant responses to Pi starvation. Furthermore, it is shown that Pi-starved hps4 mutants accumulate more auxin in their root tips than the wild type, which may explain the increased inhibition of their primary root growth when grown under Pi deficiency.