AXR1 is involved in BR-mediated elongation and SAUR-AC1 gene expression in Arabidopsis

Limited information is available concerning the interactions between the brassinosteroid (BR) and auxin signaling pathways. The expression pattern of the SAUR-AC1 gene, an early auxin-inducible gene in Arabidopsis, was studied in response to brassinolide (BL), in the presence of a BR-biosynthesis inhibitor, in a BR-deficient mutant, and in combination with auxin. The results suggested that the SAUR-AC1 gene is regulated by BRs independently of auxin levels, and that it is important in BR-mediated elongation. The axr1 (auxin insensitive 1) mutant was less sensitive to BL-induced elongation and BL-induced SAUR-AC1 expression, suggesting that a ubiquitin ligase-mediated system is involved in BR-mediated elongation.     

Characterization of a Small Auxin-Up RNA (SAUR)-Like Gene Involved in Arabidopsis thaliana Development

The root of Arabidopsis thaliana is used as a model system to unravel the molecular nature of cell elongation and its arrest. From a micro-array performed on roots that were treated with aminocyclopropane-1-carboxylic acid (ACC), the precursor of ethylene, a Small auxin-up RNA (SAUR)-like gene was found to be up regulated. As it appeared as the 76th gene in the family, it was named SAUR76. Root and leaf growth of overexpression lines ectopically expressing SAUR76 indicated the possible involvement of the gene in the division process. Using promoter::GUS and GFP lines strong expression was seen in endodermal and pericycle cells at the end of the elongation zone and during several stages of lateral root primordia development. ACC and IAA/NAA were able to induce a strong up regulation of the gene and changed the expression towards cortical and even epidermal cells at the beginning of the elongation zone. Confirmation of this up regulation of expression was delivered using qPCR, which also indicated that the expression quickly returned to normal levels when the inducing IAA-stimulus was removed, a behaviour also seen in other SAUR genes. Furthermore, confocal analysis of protein-GFP fusions localized the protein in the nucleus, cytoplasm and plasma membrane. SAUR76 expression was quantified in several mutants in ethylene and auxin-related pathways, which led to the conclusion that the expression of SAUR76 is mainly regulated by the increase in auxin that results from the addition of ACC, rather than by ACC itself.     

Arabidopsis SMALL AUXIN UP RNA63 promotes hypocotyl and stamen filament elongation

Auxin regulates plant growth and development in part by activating gene expression. Arabidopsis thaliana SMALL AUXIN UP RNAs (SAURs) are a family of early auxin-responsive genes with unknown functionality. Here, we show that transgenic plant lines expressing artificial microRNA constructs (aMIR-SAUR-A or -B) that target a SAUR subfamily (SAUR61-SAUR68 and SAUR75) had slightly reduced hypocotyl and stamen filament elongation. In contrast, transgenic plants expressing SAUR63:GFP or SAUR63:GUS fusions had long hypocotyls, petals and stamen filaments, suggesting that these protein fusions caused a gain of function. SAUR63:GFP and SAUR63:GUS seedlings also accumulated a higher level of basipetally transported auxin in the hypocotyl than did wild-type seedlings, and had wavy hypocotyls and twisted inflorescence stems. Mutations in auxin efflux carriers could partially suppress some SAUR63:GUS phenotypes. In contrast, SAUR63:HA plants had wild-type elongation and auxin transport. SAUR63:GFP protein had a longer half-life than SAUR63:HA. Fluorescence imaging and microsomal fractionation studies revealed that SAUR63:GFP was localized mainly in the plasma membrane, whereas SAUR63:HA was present in both soluble and membrane fractions. Low light conditions increased SAUR63:HA protein turnover rate. These results indicate that membrane-associated Arabidopsis SAUR63 promotes auxin-stimulated organ elongation.     

Small auxin upregulated RNA (SAUR) gene family in maize: Identification,evolution, and its phylogenetic comparison with Arabidopsis,rice, and sorghum

Small auxin-up RNAs(SAURs)are the early auxin-responsive genes represented by a large multigene family in plants.Here,we identified 79 SAUR gene family members from maize(Zea mays subsp.mays)by a reiterative database search and manual annotation.Phylogenetic analysis indicated that the SAUR proteins from Arabidopsis,rice,sorghum,and maize had divided into 16 groups.These genes were non-randomly distributed across the maize chromosomes,and segmental duplication and tandem duplication contributed to the expansion of the maize SAUR gene family.Synteny analysis established orthology relationships and functional linkages between SAUR genes in maize and sorghum genomes.We also found that the auxin-responsive elements were conserved in the upstream sequences of maize SAUR members.Selection analyses identified some significant site-specific constraints acted on most SAUR paralogs.Expression profiles based on microarray data have provided insights into the possible functional divergence among members of the SAUR gene family.Quantitative real-time PCR analysis indicated that some of the 10 randomly selected ZmSAUR genes could be induced at least in maize shoot or root tissue tested.The results reveal a comprehensive overview of the maize SAUR gene family and may pave the way for deciphering their function during plant development.     

The SAUR19 subfamily of SMALL AUXIN UP RNA genes promote cell expansion

The plant hormone auxin controls numerous aspects of plant growth and development by regulating the expression of hundreds of genes. SMALL AUXIN UP RNA (SAUR) genes comprise the largest family of auxin-responsive genes, but their function is unknown. Although prior studies have correlated the expression of some SAUR genes with auxin-mediated cell expansion, genetic evidence implicating SAURs in cell expansion has not been reported. The Arabidopsis SAUR19, SAUR20, SAUR21, SAUR22, SAUR23, and SAUR24 (SAUR19-24) genes encode a subgroup of closely related SAUR proteins. We demonstrate that these SAUR proteins are highly unstable in Arabidopsis. However, the addition of an N-terminal GFP or epitope tag dramatically increases the stability of SAUR proteins. Expression of these stabilized SAUR fusion proteins in Arabidopsis confers numerous auxin-related phenotypes indicative of increased and/or unregulated cell expansion, including increased hypocotyl and leaf size, defective apical hook maintenance, and altered tropic responses. Furthermore, seedlings expressing an artificial microRNA targeting multiple members of the SAUR19-24 subfamily exhibit short hypocotyls and reduced leaf size. Together, these findings demonstrate that SAUR19-24 function as positive effectors of cell expansion. This regulation may be achieved through the modulation of auxin transport, as SAUR gain-of-function and loss-of-function seedlings exhibit increased and reduced basipetal indole-3-acetic acid transport, respectively. Consistent with this possibility, SAUR19-24 proteins predominantly localize to the plasma membrane.     

Small auxin upregulated RNA （SAUR） gene family in maize： Identification,evolution, and its phylogenetic comparison with Arabidopsis,rice, and sorghum

Small auxin-up RNAs （.SAURs） are the early auxin- responsive genes represented by a large multigene family in plants. Here, we identified 79 SAUR gene family members from maize （Zea mays subsp, mays） by a reiterative database search and manual annotation. Phylogenetic analysis indicated that the SAUR proteins from Arabidopsis, rice, sorghum, and maize had divided into 16 groups. These genes were non-randomly distributed across the maize chromosomes, and segmental duplication and tandem duplication contributed to the expansion of the maize .SAUR gene family. Synteny analysis established ortholos~J relationships and functional linkages between SAUR genes in maize and sorghum genomes. We also found that the auxin-responsive elements were conserved in the upstream sequences of maize SAUR members. Selection analyses identified some significant site-specific constraints acted on most SAUR paralogs. Expression profiles based on microarray data have provided insights into the possible functional divergence among members of the .SAUR gene family. Quantitative real-time PCR analysis indicated that some of the 10 randomly selected ZmSAUR genes could be induced at least in maize shoot or root tissue tested. The results reveal a comprehensive overview of the maize .SAUR gene family and may pave the way for deciphering their function during pJant development.     

Genome-wide identification of SAUR genes in watermelon (<Emphasis Type="Italic">Citrullus lanatus</Emphasis>)

The early auxin responsive SAUR family is an important gene family in auxin signal transduction. We here present the first report of a genome-wide identification of SAUR genes in watermelon genome. We successfully identified 65 ClaSAURs and provide a genomic framework for future study on these genes. Phylogenetic result revealed a Cucurbitaceae-specific SAUR subfamily and contribute to understanding of the evolutionary pattern of SAUR genes in plants. Quantitative RT-PCR analysis demonstrates the existed expression of 11 randomly selected SAUR genes in watermelon tissues. ClaSAUR36 was highly expressed in fruit, for which further study might bring a new prospective for watermelon fruit development. Moreover, correlation analysis revealed the similar expression profiles of SAUR genes between watermelon and Arabidopsis during shoot organogenesis. This work gives us a new support for the conserved auxin machinery in plants.     

The AXR1 and AUX1 genes of Arabidopsis function in separate auxin-response pathways

The recessive mutations aux1 and axr1 of Arabidopsis confer resistance to the plant hormone auxin. The axr1 mutants display a variety of morphological defects. In contrast, the only morphological defect observed in aux1 mutants is a loss of root gravitropism. To learn more about the function of these genes in auxin response, the expression of the auxin-regulated gene SAUR-AC1 in mutant and wild-type plants has been examined. It has been found that axr1 plants display a pronounced deficiency in auxin-induced accumulation of SAUR-AC1 mRNA in seedlings as well as rosette leaves and mature roots. In contrast, the aux1 mutation has a modest effect on auxin induction of SAUR-AC1. To determine if the AUX1 and AXR1 genes interact to facilitate auxin response, plants which are homozygous for both aux1 and axr1 mutations have been constructed and characterized. The two mutations are additive in their effects on auxin response, suggesting that each mutation confers resistance by a different mechanism. However, the morphology of double mutant plants indicates that there is an inter-action between the AXR1 and AUX1 genes. In mature plants, the aux1-7 mutation acts to partially suppress the morphological defects conferred by the axr1-12 mutation. This suppression is not accompanied by an increase in auxin response, as measured by SAUR-AC1 expression, suggesting that the interaction between the AUX1 and AXR1 genes is indirect.     

SAUR15 interaction with BRI1 activates plasma membrane H+-ATPase to promote organ development of Arabidopsis

Brassinosteroids (BRs) are an important group of plant steroid hormones that regulate growth and development. Several members of the SMALL AUXIN UP RNA (SAUR) family have roles in BR-regulated hypocotyl elongation and root growth. However, the mechanisms are unclear. Here, we show in Arabidopsis (Arabidopsis thaliana) that SAUR15 interacts with cell surface receptor-like kinase BRASSINOSTEROID-INSENSITIVE 1 (BRI1) in BR-treated plants, resulting in enhanced BRI1 phosphorylation status and recruitment of the co-receptor BRI1-ASSOCIATED RECEPTOR KINASE 1. Genetic and phenotypic assays indicated that the SAUR15 effect on BRI1 can be uncoupled from BRASSINOSTEROID INSENSITIVE 2 activity. Instead, we show that SAUR15 promotes BRI1 direct activation of plasma membrane H⁺-ATPase (PM H⁺-ATPase) via phosphorylation. Consequently, SAUR15–BRI1–PM H⁺-ATPase acts as a direct, PM-based mode of BR signaling that drives cell expansion to promote the growth and development of various organs. These data define an alternate mode of BR signaling in plants.

SAUR15–BRI1-plasma membrane (PM) H+-ATPase acts as a direct, PM-based mode of brassinosteroid signaling that drives cell expansion to promote plant growth and development.     

一种受抗生素诱导的启动子的构建及活性分析

多聚ADP核糖聚合酶（PARP）受基因毒剂的特异性诱导。将拟南芥（Arabidopsis thaliana）AtPARP1基因上游长2179bp的启动子片段插入到质粒pAKK687的β-葡萄糖醛酸糖苷酶（GUS）报告基因上游,转化拟南芥。GUS组织化学染色结果表明,GUS报告基因仅在苗龄3-5天的拟南芥根部及花发育早期的雄蕊中表达;1.5μg.mL-1博莱霉素与22μg.mL-1丝裂霉素联用强烈诱导了GUS报告基因的表达（尤其在拟南芥的幼苗和果荚中）。进一步降低抗生素浓度,发现单独使用1μg.mL-1博莱霉素对GUS报告基因也具较强的诱导活性,且对拟南芥幼苗的生长无影响。上述结果表明,AtPARP1启动子是一个新型的具较大应用潜力的抗生素诱导型启动子。     

葡萄SAUR基因家族鉴定与生物信息学分析

为了研究葡萄早期应答生长素基因SAUR(Small auxin-up RNA)家族,本研究利用全基因组信息鉴定了葡萄64个SAUR家族成员,并对SAUR家族成员的基因结构、氨基酸特性、染色体定位、基因进化、基因功能以及组织表达进行分析。结果表明,葡萄全基因组上64个SAUR家族成员在19条染色体中的8条染色体上呈现簇状分布,主要分布在3、4号染色体上,其中3号染色体上数量最多为37个;葡萄SAUR家族基因长度较短,有59个基因是无内含子基因;蛋白理化特征分析显示,多数SAUR蛋白呈碱性,结构稳定性较差,蛋白脂溶指数高,呈亲水性;基因功能预测结果表明,葡萄SAUR基因主要担当生长因子、结构蛋白、转录、转录调控以及响应胁迫应答和免疫应答6种功能,其中更多参与生长调节功能;根据系统进化分析将其分为10个分支,另外不同组织表达谱的分析结果表明SAUR基因家族成员具有不同的组织表达模式,对于非生物胁迫具有一定的调节作用。这些信息为葡萄SAUR基因家族功能分析奠定了一定的工作基础。     

SAUR Inhibition of PP2C-D Phosphatases Activates Plasma Membrane H+-ATPases to Promote Cell Expansion in Arabidopsis

The plant hormone auxin promotes cell expansion. Forty years ago, the acid growth theory was proposed, whereby auxin promotes proton efflux to acidify the apoplast and facilitate the uptake of solutes and water to drive plant cell expansion. However, the underlying molecular and genetic bases of this process remain unclear. We have previously shown that the SAUR19-24 subfamily of auxin-induced SMALL AUXIN UP-RNA (SAUR) genes promotes cell expansion. Here, we demonstrate that SAUR proteins provide a mechanistic link between auxin and plasma membrane H⁺-ATPases (PM H⁺-ATPases) in Arabidopsis thaliana. Plants overexpressing stabilized SAUR19 fusion proteins exhibit increased PM H⁺-ATPase activity, and the increased growth phenotypes conferred by SAUR19 overexpression are dependent upon normal PM H⁺-ATPase function. We find that SAUR19 stimulates PM H⁺-ATPase activity by promoting phosphorylation of the C-terminal autoinhibitory domain. Additionally, we identify a regulatory mechanism by which SAUR19 modulates PM H⁺-ATPase phosphorylation status. SAUR19 as well as additional SAUR proteins interact with the PP2C-D subfamily of type 2C protein phosphatases. We demonstrate that these phosphatases are inhibited upon SAUR binding, act antagonistically to SAURs in vivo, can physically interact with PM H⁺-ATPases, and negatively regulate PM H⁺-ATPase activity. Our findings provide a molecular framework for elucidating auxin-mediated control of plant cell expansion.     

Evaluation of the use of the tobacco PR-1a promoter to monitor defense gene expression by the luciferase bioluminescence reporter system

Because of their marked responsiveness to induction signals, genes encoding pathogenesis-related proteins are used as markers to monitor defense gene expression in plants. To develop a non-invasive bioluminescence reporter assay system, we tested acidic PR-1 gene promoters from tobacco and Arabidopsis. These two promoters share common regulatory elements and are believed to show similar responsiveness to various stimuli but the results of transient expression assays by microprojectile bombardment of various plant cells and npr1 mutant Arabidopsis suggest that the tobacco PR-1a promoter is superior to its Arabidopsis counterpart in terms of responsiveness to salicylic acid treatment. Transgenic Arabidopsis seedlings harboring the tobacco PR-1a promoter fused to firefly luciferase showed marked induction in response to treatment with chemicals that induce defense gene expression in plants. These results suggest that the tobacco PR-1a promoter is applicable in monitoring defense-gene expression in various plant species.     

Immunolocalization of the PmSUC1 sucrose transporter in Plantago major flowers and reporter-gene analyses of the PmSUC1 promoter suggest a role in sucrose release from the inner integument

This paper presents a detailed analysis of the PmSUC1 gene from plantago major, of its promoter activity in Arabidopsis, and of the tissue specific localization of the encoded protein in Plantago. PmSUC1 promoter activity was detected in the innermost layer of the inner integument (the endothel) of Arabidopsis plants expressing the gene of the green fluorescent protein (GFP) under the control of the PmSUC1 promoter. This promoter activity was confirmed with a PmSUC1-specific antiserum that identified the PmSUC1 protein in the endothel of Plantago and of Arabidopsis plants expressing the PmSUC1 gene under the control of its own promoter. PmSUC1 promoter activity and PmSUC1 protein were also detected in pollen grains during maturation inside the anthers and in pollen tubes during and after germination. These results demonstrate that PmSUC1 is involved in sucrose partitioning to the young embryo and to the developing pollen and growing pollen tube. In the innermost cell layer of the inner integument, a tissue that delivers nutrients to the endosperm and the embryo, PmSUC1 may catalyze the release of sucrose into the apoplast.