过表达水稻OsPIN2通过减弱地上部重力反应增大分蘖角度

地上部向重力性与分蘖角度形成紧密相关,解析其调控机制有助于合理设计分蘖角度,从而促进作物株型改良。在水稻生长素输出载体基因OsPIN2过表达株系中鉴定到2个分蘖角度显著增大的株系OE-OsPIN2-1/2。扫描电镜观察显示OE-OsPIN2-1/2分蘖基部的近地端与远地端近乎对称生长。向重力性检测发现OE-OsPIN2-1/2幼苗地上部重力反应降低,且重力刺激后生长素标志基因OsIAA20和WUSCHEL相关同源盒基因WOX6/11不对称表达减弱,表明过表达OsPIN2减弱重力作用下的生长素不对称分布。此外,OE-OsPIN2-1/2分蘖基部参与重力反应的正调控基因下调表达而负调控基因上调表达,进一步表明过表达OsPIN2能够减弱地上部重力反应。本研究结果揭示了OsPIN2通过调控地上部向重力性从而控制水稻分蘖角度的机制,为深入研究植物地上部重力反应提供理论依据。

植物向重力反应中PIN-FORMED介导的生长素极性运输调控

植物的向性,即植物对光或重力等环境刺激信号产生的定向生长反应。在向重力性反应中,植物器官将重力感知为定向环境信号,来控制其器官的生长方向以促进生存。植物激素生长素及其极性运输在植物向重力反应中起着决定性的调控作用。质膜定位的生长素输出蛋白PIN-FORMED(PIN)通过动态的亚细胞极性定位,改变生长素运输的方向以响应环境刺激,由此植物器官间建立的生长素浓度梯度是细胞差异化伸长和器官弯曲的基础,来调控植物的形态建成和生长发育过程。本文主要讨论发生在植物重力感受细胞内早期重力感知和信号转导机制的最新研究进展、PIN介导的生长素极性运输、PIN的极性定位以及质膜蛋白丰度的调控机制等。

Transcriptional regulation of MdPIN7 by MdARF19 during gravityinduced formation of adventitious root GSA in self-rooted apple stock

Self-rooted apple stock is widely used for apple production.However,the shallowness of the adventitious roots in self-rooted apple stock leads to poor performance in the barren orchards of China.This is because of the considerable difference in the development of a gravitropic set-point angle(GSA)between self-rooted apple stock and seedling rootstock.Therefore,it is crucial to study the molecular mechanism of adventitious root GSA in self-rooted apple stock for breeding self-rooted and deep-rooted apple rootstock cultivars.An apple auxin response factor MdARF19 functioned to establish the adventitious root GSA of self-rooted apple stock in response to gravity and auxin signals.MdARF19 bound directly to the MdPIN7 promoter,activating its transcriptional expression and thus regulating the formation of the adventitious root GSA in 12-2 self-rooted apple stock.However,MdARF19 influenced the expression of auxin efflux carriers(MdPIN3 and MdPIN10)and the establishment of adventitious root GSA of self-rooted apple stock in response to gravity signals by direct activation of MdFLP.Our findings provide new information on the transcriptional regulation of MdPIN7 by auxin response factor MdARF19 in the regulation of the adventitious root GSA of self-rooted apple stock in response to gravity and auxin signals.

The IDD Transcription Factors:Their Functions in Plant Development and Environmental Response

INDETERMINATE-DOMAIN proteins(IDDs)are a plant-specific transcription factor family characterized by a conserved ID domain with four zinc finger motifs.Previous studies have demonstrated that IDDs coordinate a diversity of physiological processes and functions in plant growth and development,including floral transition,plant architecture,seed and root development,and hormone signaling.In this review,we especially summarized the latest knowledge on the functions and working models of IDD members in Arabidopsis,rice,and maize,particularly focusing on their role in the regulatory network of biotic and abiotic environmental responses,such as gravity,temperature,water,and pathogens.Understanding these mechanisms underlying the function of IDD proteins in these processes is important for improving crop yields by manipulating their activity.Overall,the review offers valuable insights into the functions and mechanisms of IDD proteins in plants,providing a foundation for further research and potential applications in agriculture.

LAZY1 controls rice shoot gravitropism through regulating polar auxin transport

Tiller angle of rice （Oryza sativa L.） is an important agronomic trait that contributes to grain production, and has long attracted attentions of breeders for achieving ideal plant architecture to improve grain yield. Although enormous efforts have been made over the past decades to study mutants with extremely spreading or compact tillers, the molecular mechanism underlying the control of tiller angle of cereal crops remains unknown. Here we report the cloning of the LAZY1 （LA1） gene that regulates shoot gravitropism by which the rice tiller angle is controlled. We show that LA1, a novel grass-specific gene, is temporally and spatially expressed, and plays a negative role in polar auxin transport （PAT）. Loss-of-function of LA1 enhances PAT greatly and thus alters the endogenous IAA distribution in shoots, leading to the reduced gravitropism, and therefore the tiller-spreading phenotype of rice plants.

The role of Arabidopsis 5PTase13 in root gravitropism through modulation of vesicle trafficking

Inositol polyphosphate 5-phosphatases （5PTases） are enzymes of phosphatidylinositol metabolism that affect various aspects of plant growth and development. Arabidopsis 5PTasel3 regulates auxin homeostasis and hormonerelated cotyledon vein development, and here we demonstrate that its knockout mutant 5pt13 has elevated sensitivity to gravistimulation in root gravitropic responses. The altered responses of 5pt13 mutants to 1-N-naphthylphthalamic acid （an auxin transport inhibitor） indicate that 5PTase13 might be involved in the regulation of auxin transport. Indeed, the auxin efflux carrier PIN2 is expressed more broadly under 5PTasel3 deficiency, and observations of the internalization of the membrane-selective dye FM4-64 reveal altered vesicle trafficking in 5pt13 mutants. Compared with wild-type, 5pt13 mutant seedlings are less sensitive to the inhibition by brefeldin A of vesicle cycling, seedling growth, and the intracellular cycling of the PIN1 and PIN2 proteins. Further, auxin redistribution upon gravitropic stimulation is stimulated under 5PTasel3 deficiency. These results suggest that 5PTasel3 may modulate auxin transport by regulating vesicle trafficking and thereby play a role in root gravitropism.

Identification of a Gravitropism-Deficient Mutant in Rice

A gravitropism-deficient mutant M96 was isolated from a mutant bank, generated by ethyl methane sulfonate(EMS) mutagenesis of indica rice accession ZJ100. The mutant was characterized as prostrate growth at the beginning of germination, and the prostrate growth phenotype ran through the whole life duration. Tiller angle and tiller number of M96 increased significantly in comparison with the wild type. Tissue section observation analysis indicated that asymmetric stem growth around the second node occurred in M96. Genetic analysis and gene mapping showed that M96 was controlled by a single recessive nuclear gene, tentatively termed as gravitropism-deficient M96(gd M96), which was mapped to a region of 506 kb flanked by markers RM5960 and In Del8 on the long arm of chromosome 11. Sequencing analysis of the open reading frames in this region revealed a nucleotide substitution from G to T in the third exon of LOC_Os11g29840. Additionally, real-time fluorescence quantitative PCR analysis showed that the expression level of LOC_Os11g29840 in the stems was much higher than in the roots and leaves in M96. Furthermore, the expression level was more than four times in M96 stem than in the wild type stem. Our results suggested that the mutant gene was likely a new allele to the reported gene LAZY1. Isolation of this new allele would facilitate the further characterization of LAZY1.

Characterization of wavy root 1,an agravitropism allele,reveals the functions of OsPIN2 in fine regulation of auxin transport and distribution and in ABA biosynthesis and response in rice(Oryza sativa L.)

Root system architecture is influenced by gravity.How the root senses gravity and directs its orientation,so-called gravitropism,is not only a fundamental question in plant biology but also theoretically important for genetic improvement of crop root architecture.However,the mechanism has not been elucidated in most crops.We characterized a rice agravitropism allele,wavy root 1(war1),a loss-of-function allele in OsPIN2,which encodes an auxin efflux transporter.With loss of OsPIN2 function,war1 leads to altered root system architecture including wavy root,larger root distribution angle,and shallower root system due to the loss of gravitropic perception in root tips.In the war1 mutant,polar auxin transport was disrupted in the root tip,leading to abnormal auxin levels and disturbed auxin transport and distribution in columella cells.Amyloplast sedimentation,an important process in gravitropic sensing,was also decreased in root tip columella cells.The results indicated that OsPIN2 controls gravitropism by finely regulating auxin transport,distribution and levels,and amyloplast sedimentation in root tips.We identified a novel role of OsPIN2 in regulating ABA biosynthesis and response pathways.Loss of OsPIN2 function in the war1 resulted in increased sensitivity to ABA in seed germination,increased ABA level,changes in ABA-associated genes in roots,and decreased drought tolerance in the seedlings.These results suggest that the auxin transporter OsPIN2 not only modulates auxin transport to control root gravitropism,but also functions in ABA signaling to affect seed germination and root development,probably by mediating crosstalk between auxin and ABA pathways.

Arabidopsis Phytochrome D Is Involved in Red Light-Induced Negative Gravitropism of Hypocotyles

The phytochrome gene family, which is in Arabidopsis thaliana, consists of phytochromes A-E（phyA to phyE）, regulates plant responses to ambient light environments. PhyA and phyB have been characterized in detail, but studies on phyC to phyE have reported discrepant functions. In this study, we show that phyD regulates the Arabidopsis gravitropic response by inhibiting negative gravitropism of hypocotyls under red light condition. PhyD had only a limited effect on the gravitropic response of roots in red light condition. PhyD also enhanced phyB-regulated gravitropic responses in hypocotyls. Moreover, the regulation of hypocotyl gravitropic responses by phyD was dependent upon the red light fluence rate.

PROG1 acts upstream of LAZY1 to regulate rice tiller angle as a repressor

Rice tiller angle,as a component of plant architecture,affects rice grain yield via plant density.However,the molecular mechanism underlying rice tiller angle remains elusive.We report that the key domestication gene PROSTRATE GROWTH 1(PROG1)controls rice tiller angle by regulating shoot gravitropism and LAZY1(LA1)-mediated asymmetric distribution of auxin.Acting as a transcriptional repressor,PROG1 negatively regulates the expression of LA1 in light-grown rice seedlings.Overexpression of LA1 partially rescued the larger tiller angle of the PROG1 complementation transgenic plant(prog1-D).Double-mutant analysis showed that PROG1 acts upstream of LA1 to regulate shoot gravitropism and tiller angle.Mutation of Suppressors of lazy1(SOL1),encoding DWARF3(D3)acting in the strigolactone signal pathway,suppressed the large tiller angle of prog1-D by rescuing the transcription of LA1.The discovery of a light-sensitive PROG1-LA1 transcription regulatory module controlling rice shoot gravitropism and tiller angle sheds light on the genetic control of rice tiller angle.

Light-stabilized GIL1 suppresses PIN3 activity to inhibit hypocotyl gravitropism

Light and gravity coordinately regulate the directional growth of plants.Arabidopsis Gravitropic in the Light 1(GIL1)inhibits the negative gravitropism of hypocotyls in red and far-red light,but the underlying molecular mechanisms remain elusive.Our study found that GIL1 is a plasma membrane-localized protein.In endodermal cells of the upper part of hypocotyls,GIL1 controls the negative gravitropism of hypocotyls.GIL1 directly interacts with PIN3 and inhibits the auxin transport activity of PIN3.Mutation of PIN3 suppresses the abnormal gravitropic response of gil1 mutant.The GIL1 protein is unstable in darkness but it is stabilized by red and far-red light.Together,our data suggest that light-stabilized GIL1 inhibits the negative gravitropism of hypocotyls by suppressing the activity of the auxin transporter PIN3,thereby enhancing the emergence of young seedlings from the soil.

LAZY4 acts additively with the starch-statolithdependent gravity-sensing pathway to regulate shoot gravitropism and tiller angle in rice

Rice tiller angle is a key agronomic trait that has significant effects on the establishment of a high-yield rice population.However,the molecular mechanism underlying the control of rice tiller angle remains to be clarified.Here,we characterized the novel tiller-angle gene LAZY4(LA4)in rice through map-based cloning.LA4 encodes a C3H2C3-type RING zinc-finger E3 ligase localized in the nucleus,and an in vitro ubiquitination assay revealed that the conserved RING finger domain is essential for its E3 ligase activity.We found that expression of LA4 can be induced by gravistimulation and that loss of LA4 function leads to defective shoot gravitropism caused by impaired asymmetric auxin redistribution upon gravistimulation.Genetic analysis demonstrated that LA4 acts in a distinct pathway from the starch biosynthesis regulators LA2 and LA3,which function in the starch-statolith-dependent pathway.Further genetic analysis showed that LA4 regulates shoot gravitropism and tiller angle by acting upstream of LA1 to mediate lateral auxin transport upon gravistimulation.Our studies reveal that LA4 regulates shoot gravitropism and tiller angle upstream of LA1 through a novel pathway independent of the LA2-LA3-mediated gravity-sensing mechanism,providing new insights into the rice tiller-angle regulatory network.

菜豆根构型对低磷胁迫的适应性变化及基因型差异

利用特殊设计的营养袋纸培和分层式磷控释砂培等根系生长系统结合计算机图像分析技术 ,以基根根长在生长介质各层的相对分布和基根平均生长角度为指标 ,定量测定菜豆 (PhaseolusvulgarisL .)根构型在低磷胁迫下的适应性变化及其与磷效率的关系。结果表明 ,菜豆根构型对低磷胁迫具有适应性反应 ,在缺磷条件下基根向地性减弱 ,基根在生长介质表层相对分布增多、基根平均生长角度 (与水平线夹角 )变小 ,从而导致整个根系较浅。供试菜豆根构型对低磷胁迫的适应性反应具有显著基因型差异 ,缺磷时G19833等基因型向地性明显减弱 ,基根向高磷剖面趋向生长的能力较强 ,因而具有较高的磷吸收效率。研究结果表明根构型变化是菜豆适应低磷胁迫的可能机理之一 ,为通过改变植物根构型来提高磷吸收效率提供了依据。

植物根系向地性感应的分子机理与养分吸收

植物根系向地性是决定根系空间生长趋势的主要因素之一,对于养分吸收具有重要影响。认识根系向地性感应和根系生长变化的分子机理及其与养分吸收的关系,可为遗传改良根系性状、提高植物养分吸收效率提供理论依据。本文从重力感应、信号转导和生长素非对称分布等方面总结了植物根系向地性感应的分子机理,探讨了根系在养分胁迫下(特别是磷胁迫下)向地性变化的生理基础及其与养分吸收(特别是磷吸收)的关系,最后对根系向地性研究的若干问题进行了展望。

外源Ca^(2+)及其相关物质对抛秧稻立苗的影响

本研究用不同浓度的外源Ｃａ２＋及其相关物质处理水稻秧苗，然后将秧苗水平放置，观察它们 对立苗的影响。结果表明：外源Ｃａ２＋处理促进了立苗速度和立苗幅度的提高，而不利于Ｃａ２＋浓度增加 的因素，如 Ｃａ２＋螫合剂 ＥＤＴＡ、 Ｃａ２＋通道抑制剂 ＴＦＰ处理，都抑制了水平放置苗的立苗。这从实践上 证明了Ｃａ２＋在调节植物正、负向重性反应中具有重要的作用。

拟南芥PIN2介导的生长素极性运输调控植物根向地性

主要观察了拟南芥生长素输出载体PIN2及其介导的极性运输、生长素诱导合成对根尖生长素不对称分布和根向地性反应的影响.结果表明:拟南芥PIN2基因突变、诱导内源生长素IAA及用抑制剂NPA或TIBA抑制生长素极性运输都严重影响了根尖生长素不对称分布的形成,最终抑制植物根向地性反应,暗示PIN2介导的生长素极性运输和生长素不对称分布在根向地性反应中起着关键性调控作用.从这些研究结果可进一步理解生长素调控植物根向地性的分子机理.

高铵胁迫对拟南芥根系向重性的影响及机制初探

向重性是决定植物根系构型的主要因素之一，对根系锚定及水分养分吸收具有重要影响。铵显著影响拟南芥根构型，尽管高铵抑制主根伸长和侧根数，然而铵对主根生长方向的研究却少有报道。本文以拟南芥为材料，利用室内培养基模拟试验，研究了高铵胁迫对根系向重性生长的影响，发现高铵胁迫不仅抑制植物生长，还影响主根的生长方向。0-30h动态观测结果表明：10mmol／L（NH4）2S04对根系的向重性反应仅表现为延缓效应，而30mmol／L（NH4）2SO4则显著减弱主根的向重性弯曲。降低基本培养基养分浓度后，铵对主根向重性反应的抑制效应可发生在较低的NH4＋浓度。外源添加Ca^2＋可部分恢复铵对主根伸长的抑制效应，却不能缓解铵对主根向重性反应的影响。不同部位分开供铵，结果显示铵对拟南芥主根向重性的影响主要是根部铵效应。上述结果表明，铵对主根向重性的影响机制部分独立于其对主根伸长的影响，也不是由于Ca^2＋缺乏引起的，而有可能与根部高铵诱导的根尖其他生理活动过程改变有关。

钙离子在向光性和向重性反应信号转导中的作用

Ca2+作为细胞内、外信号的重要的第二信使,在向性运动的信号转导中起了重要的调节作用,着重综述了Ca2+在向光性和向重性运动的信号转导中的作用。通过综述可以推测,Ca2+刺激诱导细胞质Ca2+浓度变化,可能是协调植物对环境反应的通用机制。

超量表达细胞D型周期蛋白CYCD3;1影响拟南芥根的发育

用雌激素诱导表达的启动子(XVE启动子)超量表达CYCD3;1的结果表明CYCD3;1的超量表达不仅抑制拟南芥初生根的伸长,而且还抑制初生根对重力刺激的反应能力。

水稻向地性突变体的鉴定与遗传和定位分析

从水稻籼稻品种E优428的诱变M1代群体中获得向地性突变体la(t),该突变体在苗期倒伏生长,成熟期呈匍匐型生长,其它性状未发现异常。初步的生理研究表明该突变体不受外源激素(2,4-D,赤酶素)和光照的影响,并失去了感受重力的能力。遗传分析表明,该突变属单基因隐性突变,将该基因暂定名为la(t)。利用该突变体与籼稻品种D62B杂交,构建了F2代分离群体,用微卫星标记分析,将该基因定位于水稻第11染色体上的微卫星标记Lu2和Lu18之间,与目的基因分别相距1.0和1.7cM。通过电子杂交的方法将该基因所在区域的遗传图谱整合到国际水稻基因组计划的水稻第11染色体物理图谱中,其la(t)基因两端毗连的Lu2和Lu18SSR标记之间的物理距离约为140～200kb。为用图位克隆法分离此目的基因和研究水稻向地性生长的分子机理奠定基础。