Leukamenin E调节拟南芥幼苗根部生长素极性运输及根系生长发育

本文采用14种拟南芥转基因报告株系,研究了对映-贝壳杉烷二萜(leukamenin E)调节拟南芥根部生长素极性运输转运蛋白表达并影响根生长发育的机制。结果表明:leukamenin E浓度在20～40μmol·L~(-1)范围显著抑制拟南芥幼苗主根的生长,较低浓度leukamenin E(10μmol·L~(-1))促进侧根提前发生并增加侧根数量; 10～30μmol·L-1的leukamenin E在处理拟南芥幼苗48 h后可显著提高其根尖部生长素水平;进一步检测根部生长素极性运输转运蛋白表达,发现该浓度条件下leukamenin E促进PIN1在转录水平表达并增加其蛋白丰度,但在转录水平抑制PIN2表达并减少其蛋白丰度;同时,显著减少PIN3、PIN7和PIN4蛋白在小柱和静止中心及其周围细胞的丰度以及AUX1的定位丰度; Leukamenin E对PIN1丰度的上调以及对PIN2、PIN3、PIN4、PIN7和AUX1定位丰度的减少可导致生长素在根尖顶部的积累以及根部生长素浓度梯度的改变,引起根生长的抑制及侧根的提前发生。     

Rabdosinate调节生长素极性运输蛋白PIN1、PIN3和PIN4抑制拟南芥幼苗根生长

利用3种拟南芥生长素极性运输外运载体突变体及4种转基因株系研究了二萜rabdosinate抑制拟南芥幼苗主根及侧根生长的作用机制。结果显示,60~80 μmol·L^-1的rabdosinate显著抑制野生型拟南芥幼苗主根生长及侧根形成,而对突变体pin1、pin2和pin3主根未显示明显的抑制效应,对侧根的抑制减弱;发现rabdosinate （60~80 μmol·L^-1）引起生长素报告株系根尖DR5活性升高,并增加融合蛋白PIN1-GFP丰度以及减少PIN3-GFP和PIN4-GFP的丰度。推断rabdosinate可通过增加PIN1丰度促进了根部生长素向顶运输,而减少PIN3丰度降低根尖部生长素的横向转运,引起了生长素在根尖部的累积及生长素浓度梯度的改变,进而抑制幼苗主根生长及侧根发育。     

头孢霉素对拟南芥主根生长发育的影响

以拟南芥野生型和相关转基因株系为材料,设置0、50、100、200和400μg/mL头孢霉素处理,考察头孢霉素对主根伸长生长、根尖分生组织活性、生长素分布运输以及干细胞活性的影响,探究头孢霉素对拟南芥主根生长发育的毒性作用机制。结果显示:(1)头孢霉素能以浓度依赖的方式抑制拟南芥主根的生长,并抑制分生组织长度和CYCB1;1基因的表达,说明它能抑制根尖分生组织活性。(2)头孢霉素能降低根尖生长素报告基因DR5∷GUS、DR5∷GFP和生长素极性运输蛋白PIN1、PIN2、PIN3、PIN7和AUX1的表达,说明它能抑制根尖生长素的分布和极性运输。(3)头孢霉素能下调根尖静止中心标记系WOX5∷GFP、QC25和QC46的表达,以及SHR和SCR蛋白的表达,说明它能抑制根尖干细胞活性。研究表明,头孢霉素能通过抑制根尖分生组织活性、生长素的分布和极性运输以及干细胞活性,从而调节拟南芥主根的生长发育。     

铝胁迫对拟南芥根尖AtPIN2蛋白表达活性的影响

铝胁迫能影响根尖生长素的运输,这与生长素运输载体密切相关,PIN2作为根尖生长素的运输蛋白,其独特的组织定位可能诱导PIN2蛋白参与了铝调节生长素的运输过程。该研究以拟南芥PIN2缺失突变体(pin2)、PIN2□∷□GFP融合体及其野生型(WT)为材料,应用激光扫描共聚焦显微技术,研究铝处理对拟南芥根尖生长素运输蛋白PIN2的表达活性、蛋白在组织及亚细胞水平分布及其对铝内置化作用的影响。结果表明:短期铝处理或低铝浓度能明显增加拟南芥根尖细胞PIN2蛋白表达活性,而长期铝处理或高铝浓度抑制其表达活性;以100μmol·L-1Al Cl3处理4 h的蛋白表达活性最高。蛋白印迹反应发现,铝处理促进PIN2蛋白在细胞膜上累积,减少胞内囊泡中PIN2蛋白的含量;囊泡运输抑制剂(BFA)能抑制铝诱导PIN2蛋白的分配。铝胁迫增加拟南芥根尖细胞H2O2累积,pin2的H2O2累积量大于WT,而相对根长小于WT。Morin染色结果显示,pin2的铝内置化显著小于WT。上述研究表明,PIN2蛋白在100μmol·L-1Al Cl3处理条件下活性最高,细胞膜累积程度加强,铝内置化能力增强,从而调节根系的生长发育。该研究结果进一步为铝抑制生长素的运输机制提供了理论基础。     

铝胁迫对拟南芥根尖ＡｔＰＩＮ２ 蛋白表达活性的影响

铝胁迫能影响根尖生长素的运输,这与生长素运输载体密切相关,PIN2作为根尖生长素的运输蛋白,其独特的组织定位可能诱导PIN2蛋白参与了铝调节生长素的运输过程。该研究以拟南芥PIN2缺失突变体( pin2)、PIN2□∷□GFP融合体及其野生型( WT)为材料,应用激光扫描共聚焦显微技术,研究铝处理对拟南芥根尖生长素运输蛋白PIN2的表达活性、蛋白在组织及亚细胞水平分布及其对铝内置化作用的影响。结果表明：短期铝处理或低铝浓度能明显增加拟南芥根尖细胞PIN2蛋白表达活性,而长期铝处理或高铝浓度抑制其表达活性;以100μmol?L-1 AlCl3处理4 h的蛋白表达活性最高。蛋白印迹反应发现,铝处理促进PIN2蛋白在细胞膜上累积,减少胞内囊泡中PIN2蛋白的含量;囊泡运输抑制剂( BFA)能抑制铝诱导PIN2蛋白的分配。铝胁迫增加拟南芥根尖细胞H2 O2累积,pin2的H2 O2累积量大于WT,而相对根长小于WT。 Morin染色结果显示,pin2的铝内置化显著小于WT。上述研究表明,PIN2蛋白在100μmol?L-1 AlCl3处理条件下活性最高,细胞膜累积程度加强,铝内置化能力增强,从而调节根系的生长发育。该研究结果进一步为铝抑制生长素的运输机制提供了理论基础。     

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。     

生长素调控根向重力性在植物激素实验教学中的应用

根是植物重要的器官,其向重力生长是由生长素的浓度与分布所调控的,是植物对环境信号作出的生理反应。本文对模式植物拟南芥的根进行改变重力方向的刺激,借助含有响应生长素的分子标记的DR5rev:GFP、DR5:3xVenus和DR5:GUS转基因株系,可视化在重力方向改变刺激下根尖两侧的生长素不对称分布,同时观察生长素极性运输载体的相关突变体pin2-T、aux1-T在重力方向改变刺激下的表型,帮助学生深入理解生长素调控拟南芥根向重力生长的生理机制。     

AtPIN2基因通过影响根尖抗氧化能力参与拟南芥耐铝响应

PIN2是根尖生长素运输的重要蛋白,PIN2基因的差异表达是否影响植物耐铝性并不清楚。本文以不同At PIN2表达水平的拟南芥为材料,研究了At PIN2差异表达对拟南芥耐铝性的影响。结果表明,铝处理明显增强拟南芥根尖0~5 mm区域At PIN2基因的转录表达,与对照相比,其表达量增加了80%。铝能诱导PIN2蛋白在根尖细胞膜水平方向累积,并且呈束状分布。通过分析不同At PIN2表达材料的耐铝性,发现在铝处理条件下,PIN2缺失突变体(pin2-ko)的根系伸长速率显著小于PIN2超表达(PIN2-OX)和野生型材料(Col);并且,pin2-ko累积较多的活性氧;pin2-ko的SOD、CAT和APX活性以及GSH含量均显著低于PIN2-OX。上述结果表明,At PIN2表达差异影响拟南芥耐铝性,敲除At PIN2导致其对铝毒更敏感,其机理可能是At PIN2通过影响根尖抗氧化能力参与拟南芥耐铝响应。     

PIN蛋白在生长素极性运输中的作用

PIN蛋白是生长素流出栽体,它在细胞中的不对称分布决定细胞间生长素流方向.PIN蛋白网络系统决定生长素的极性运输,为植物体各部位的细胞提供了特异的位置和方向信息.从细胞水平上介绍PIN蛋白在生长素极性运输中的作用及对PIN蛋白功能调节的研究进展.     

多胺生物合成抑制剂D-精氨酸对拟南芥幼苗根系生长的影晌

为探讨多胺生物合成抑制剂D-精氨酸（D-arginine,D-Arg）对拟南芥根系生长的影响,首先用腐胺（0．1mmol‘L-1）和D—Arg（1．0mmol·L-1）处理种子萌发后生长2d的拟南芥幼苗。腐胺（0．1mmol·L-1）显著促进主根伸长,D-Arg（1．0mmol-L-1）显著抑制主根伸长,并对主根根尖的细胞形态有明显影响。为了进一步了解D—Arg影响拟南芥主根生长的机理,采用浓度梯度D．Arg处理幼苗根系。实验结果表明,随着D-Arg浓度增加（0．2～1．0mmol·L-1）,拟南芥幼苗主根生长受抑制的程度越严重。微分干涉观察主根根尖发现,外源施加D—Arg,引起拟南芥主根根尖分生区的细胞数目减少,使拟南芥幼苗表现出主根的伸长生长变缓。当分生区数目较少时,出现主根几乎不再仲长的现象。由此推测,多胺生物合成抑制剂D-Arg对拟南芥幼苗根生长的抑制作用机制,是D-Arg影响了其根尖分生区的细胞分裂活动,使分生区细胞数目减少,从而引起分生区长度减小,最终导致拟南芥主根仲长生长受到抑制。     

Exogenous auxin affects ascorbate metabolism in roots of tomato seedlings

Ascorbate levels and redox states, as well as the activities of the enzymes of ascorbate metabolism, were analyzed in roots of tomato seedlings during the culture on a medium supplemented with auxin and compared to the control cultured on an auxin-free medium. Biochemical parameters were determined separately in the distal part of the root where the inhibitory effect of auxin on root elongation growth is observed and in the proximal half on the organ which reacts to auxin treatment with increased lateral root proliferation. ASC peroxidase activity was found to be stimulated by auxin treatment in the lateral-root forming part of the root. This effect was not observed in the distal part of the organ. On the other hand, ASC oxidase activity was raised by auxin exclusively in the distal part of the root. An inhibitory effect of auxin supplementation to the medium on ASC—reducing enzymes was observed. The dehydroascorbate reductase activity was found to be inhibited by auxin only in the proximal part, while the activity of monodehydroascorbate reductase in both, the proximal and distal parts of the root. Ascorbate content increased in roots during culture irrespective of the presence of auxin. However, auxin treatment resulted in higher DHA levels and more significant participation of DHA in the total ascorbate pool when compared to the control grown on the auxin-free medium. Similar to auxin, adding DHA to the culture medium stimulated lateral root formation and inhibited primary root elongation. In contrast to DHA, ASC treatment affected significantly neither lateral root formation nor primary root growth and partly reversed the stimulatory effect of IAA on root formation and the inhibitory effect on root elongation. These results suggest that auxin induced changes in ascorbate metabolism may be involved in developmental reactions in tomato roots.     

The involvement of auxin in root architecture plasticity in Arabidopsis induced by heterogeneous phosphorus availability

Homogeneous low phosphorus availability was reported to regulate root architecture in Arabidopsis via auxin, but the roles of auxin in root architecture plasticity to heterogeneous P availability remain unclear. In this study, we employed auxin biosynthesis-, transport- and signalling-related mutants. Firstly, we found that in contrast to low P (LP) content in the whole medium, primary root (PR) growth of Arabidopsis was partially rescued in the medium divided into two parts: upper with LP and lower with high P (HP) content or in the reverse arrangement. The down part LP was more effective to arrest PR growth as well as to decrease density of lateral roots (DLR) than the upper LP, and effects were dependent on polar auxin transport. Secondly, we verified that auxin receptor TIR1 was involved in the responses of PR growth and lateral root (LR) development to P supply and loss of function of TIR1 inhibited LR development. Thirdly, effects of heterogeneous P on LRD in the upper part of PR was dependent on PIN2 and PIN4, and in the down part on PIN3 and PIN4, whereas density of total LRs was dependent on auxin transporters PIN2 and PIN7. Finally, heterogeneous P availability altered the accumulation of auxin in PR tip and the expression of auxin biosynthesisrelated genes TAA1, YUC1, YUC2, and YUC4. Taken together, we provided evidences for the involvement of auxin in root architecture plasticity in response to heterogeneous phosphorus availability in Arabidopsis.     

Blue‐light‐induced PIN3 polarization for root negative phototropic response in Arabidopsis

Root negative phototropism is an important response in plants. Although blue light is known to mediate this response, the cellular and molecular mechanisms underlying root negative phototropism remain unclear. Here, we report that the auxin efflux carrier PIN‐FORMED (PIN) 3 is involved in asymmetric auxin distribution and root negative phototropism. Unilateral blue‐light illumination polarized PIN3 to the outer lateral membrane of columella cells at the illuminated root side, and increased auxin activity at the illuminated side of roots, where auxin promotes growth and causes roots bending away from the light source. Furthermore, root negative phototropic response and blue‐light‐induced PIN3 polarization were modulated by a brefeldin A‐sensitive, GNOM‐dependent, trafficking pathway and by phot1‐regulated PINOID (PID)/PROTEIN PHOSPHATASE 2A (PP2A) activity. Our results indicate that blue‐light‐induced PIN3 polarization is needed for asymmetric auxin distribution during root negative phototropic response.     

Early development and gravitropic response of lateral roots in Arabidopsis thaliana

Root system architecture plays an important role in determining nutrient and water acquisition and is modulated by endogenous and environmental factors, resulting in considerable developmental plasticity. The orientation of primary root growth in response to gravity (gravitropism) has been studied extensively, but little is known about the behaviour of lateral roots in response to this signal. Here, we analysed the response of lateral roots to gravity and, consistently with previous observations, we showed that gravitropism was acquired slowly after emergence. Using a lateral root induction system, we studied the kinetics for the appearance of statoliths, phloem connections and auxin transporter gene expression patterns. We found that statoliths could not be detected until 1 day after emergence, whereas the gravitropic curvature of the lateral root started earlier. Auxin transporters modulate auxin distribution in primary root gravitropism. We found differences regarding PIN3 and AUX1 expression patterns between the lateral root and the primary root apices. Especially PIN3, which is involved in primary root gravitropism, was not expressed in the lateral root columella. Our work revealed new developmental transitions occurring in lateral roots after emergence, and auxin transporter expression patterns that might explain the specific response of lateral roots to gravity.     

Dynamics in PIN2 auxin carrier ubiquitylation in gravity-responding Arabidopsis roots

Plant tropisms are decisively influenced by dynamic adjustments in spatiotemporal distribution of the growth regulators auxin. Polar auxin transport requires activity of PIN-type auxin carrier proteins, with their distribution at the plasma membrane significantly contributing to the directionality of auxin flow. Control of PIN protein distribution involves regulation of their endocytosis and further sorting into the lytic vacuole for degradation and recently, protein ubiquitylation has been demonstrated to control degradative sorting of plasma membrane proteins in plants.1-6 Here we show dynamic adjustments in PIN2 ubiquitylation in gravity-stimulated roots, a response that coincides with establishment of a lateral PIN2 expression gradient. Our results imply that perception and transduction of gravity signals triggers differential ubiquitylation of PIN2, which might feed back on the coordination of auxin distribution in root meristems.     

The plant beneficial rhizobacterium Achromobacter sp. 5B1 influences root development through auxin signaling and redistribution

Roots provide physical and nutritional support to plant organs that are above ground and play critical roles for adaptation via intricate movements and growth patterns. Through screening the effects of bacterial isolates from roots of halophyte Mesquite (Prosopis sp.) on Arabidopsis thaliana, we identified Achromobacter sp. 5B1 as a probiotic bacterium that influences plant functional traits. Detailed genetic and architectural analyses in Arabidopsis grown in vitro and in soil, cell division measurements, auxin transport and response gene expression and brefeldin A treatments demonstrated that root colonization with Achromobacter sp. 5B1 changes the growth and branching patterns of roots, which were related to auxin perception and redistribution. Expression analysis of auxin transport and signaling revealed a redistribution of auxin within the primary root tip of wild‐type seedlings by Achromobacter sp. 5B1 that is disrupted by brefeldin A and correlates with repression of auxin transporters PIN1 and PIN7 in root provasculature, and PIN2 in the epidermis and cortex of the root tip, whereas expression of PIN3 was enhanced in the columella. In seedlings harboring AUX1, EIR1, AXR1, ARF7ARF19, TIR1AFB2AFB3 single, double or triple loss‐of‐function mutations, or in a dominant (gain‐of‐function) mutant of SLR1, the bacterium caused primary roots to form supercoils that are devoid of lateral roots. The changes in growth and root architecture elicited by the bacterium helped Arabidopsis seedlings to resist salt stress better. Thus, Achromobacter sp. 5B1 fine tunes both root movements and the auxin response, which may be important for plant growth and environmental adaptation.     

Glycerol Affects Root Development through Regulation of Multiple Pathways in Arabidopsis

Glycerol metabolism has been well studied biochemically. However, the means by which glycerol functions in plant development is not well understood. This study aimed to investigate the mechanism underlying the effects of glycerol on root development in Arabidopsis thaliana. Exogenous glycerol inhibited primary root growth and altered lateral root development in wild-type plants. These phenotypes appeared concurrently with increased endogenous glycerol-3-phosphate (G3P) and H₂O₂ contents in seedlings, and decreased phosphate levels in roots. Upon glycerol treatment, G3P level and root development did not change in glycerol kinase mutant gli1, but G3P level increased in gpdhc1 and fad-gpdh mutants, which resulted in more severely impaired root development. Overexpression of the FAD-GPDH gene attenuated the alterations in G3P, phosphate and H₂O₂ levels, leading to increased tolerance to exogenous glycerol, which suggested that FAD-GPDH plays an important role in modulating this response. Free indole-3-acetic acid (IAA) content increased by 46%, and DR5pro::GUS staining increased in the stele cells of the root meristem under glycerol treatment, suggesting that glycerol likely alters normal auxin distribution. Decreases in PIN1 and PIN7 expression, β-glucuronidase (GUS) staining in plants expressing PIN7pro::GUS and green fluorescent protein (GFP) fluorescence in plants expressing PIN7pro::PIN7-GFP were observed, indicating that polar auxin transport in the root was downregulated under glycerol treatment. Analyses with auxin-related mutants showed that TIR1 and ARF7 were involved in regulating root growth under glycerol treatment. Glycerol-treated plants showed significant reductions in root meristem size and cell number as revealed by CYCB1;1pro::GUS staining. Furthermore, the expression of CDKA and CYCB1 decreased significantly in treated plants compared with control plants, implying possible alterations in cell cycle progression. Our data demonstrated that glycerol treatment altered endogenous levels of G3P, phosphate and ROS, affected auxin distribution and cell division in the root meristem, and eventually resulted in modifications of root development.