Agrobacterium Tumefaciens and Crown Gall Disease
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Agrobacterium Tumefaciens and Crown Gall Disease

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Questions and Answers

What does the phloem sap predominantly contain?

  • CYP735A and riboside
  • iPRP and tZRP
  • tZ and tZ riboside
  • iP and tZ (correct)

    • What effect do the ipt1;3;5;7 mutants have on stem growth?

  • They demonstrate enhanced cambium activity.
  • They result in broad stems with high secondary growth.
  • They show increased branching and leaf size.
  • They make very narrow stems with little secondary growth. (correct)

    • What is synthesized at high levels in the roots by CYP735A?

  • tZ riboside (correct)
  • Cytokinins
  • iP
  • Phloem sap

    • How can the phenotype of ipt1;3;5;7 mutants be rescued?

    <p>By grafting with wild-type roots or shoots.</p> Signup and view all the answers

    What role do cytokinins (CKs) have in plants?

    <p>They regulate vascular cambium activity.</p> Signup and view all the answers

    What is the primary function of HPTs in plants?

    <p>Shuttling between the cytoplasm and nucleus</p> Signup and view all the answers

    What does the loss-of-function of one or two AHPs indicate about their role in cytokinin signaling?

    <p>They act somewhat redundantly in transducing cytokinin signaling.</p> Signup and view all the answers

    Which of the following characteristics is associated with the triple mutant of AHPs?

    <p>Short root characteristic of cytokinin signaling deficiency</p> Signup and view all the answers

    Based on the provided content, how do HPTs and AHPs function in cytokinin signaling?

    <p>They are necessary for transducing the signaling but can compensate for each other.</p> Signup and view all the answers

    Which protein is primarily mentioned as functioning in the transduction of cytokinin signaling?

    <p>Response regulator</p> Signup and view all the answers

    What role does the input domain play in bacterial systems?

    <p>Environmental sensing</p> Signup and view all the answers

    What mechanism mediates cytokinin signaling in plants?

    <p>Two-component-like system</p> Signup and view all the answers

    In the context of cytokinin signaling, what does HPT stand for?

    <p>Histidine Phosphotransfer protein</p> Signup and view all the answers

    How many histidine phosphotransfer proteins (HPTs) are mentioned in the context of the Arabidopsis cytokinin response pathway?

    <p>Five</p> Signup and view all the answers

    What type of signal relay is facilitated by the aspartate (D) in the response regulator?

    <p>Phosphorylation signal</p> Signup and view all the answers

    Which components are included in the Arabidopsis cytokinin response pathway?

    <p>Three CK receptors and five HPTs</p> Signup and view all the answers

    What is the role of hybrid histidine kinases in bacterial signaling?

    <p>Participate in multistep signaling</p> Signup and view all the answers

    Which of the following response regulators in Arabidopsis are also known as ARRs?

    <p>Type-A and Type-B</p> Signup and view all the answers

    What is the primary function of AHK4 in Arabidopsis?

    <p>It acts as a cytokinin receptor.</p> Signup and view all the answers

    What is the phenotype observed in cre1 mutants of Arabidopsis?

    <p>No shoot production in tissue culture.</p> Signup and view all the answers

    How can cytokinin receptor function be assessed experimentally?

    <p>Through protoplast systems and CK-induced reporter genes.</p> Signup and view all the answers

    What characterizes the activity of Arabidopsis CK receptors?

    <p>They exhibit partially redundant activities.</p> Signup and view all the answers

    What is the primary consequence of the triple mutant phenotype in Arabidopsis?

    <p>More severe responses compared to double mutants.</p> Signup and view all the answers

    Which of the following cytokinin receptors is associated with the wooden-leg (wol) mutant?

    <p>AHK4</p> Signup and view all the answers

    What effect does cytokinin have on root growth in Arabidopsis?

    <p>Inhibits root growth.</p> Signup and view all the answers

    In the context of CK response, what does the ARR6 promoter indicate?

    <p>CK-induced response activation.</p> Signup and view all the answers

    What disease is primarily caused by Agrobacterium tumefaciens?

    <p>Crown gall disease</p> Signup and view all the answers

    Which plant hormones are produced as a result of T-DNA transfer from Agrobacterium tumefaciens?

    <p>Auxin and cytokinin</p> Signup and view all the answers

    What is the primary role of the tmr gene in Agrobacterium tumefaciens?

    <p>It encodes a cytokinin biosynthetic enzyme</p> Signup and view all the answers

    What type of plasmids does Agrobacterium tumefaciens carry that contribute to tumor formation?

    <p>Tumor-inducing plasmids</p> Signup and view all the answers

    Which enzyme encoded by the tmr gene is crucial for cytokinin synthesis?

    <p>Isopentenyl-transferase</p> Signup and view all the answers

    Which statement accurately describes the differences between bacterial IPT genes and plant IPT genes?

    <p>Bacterial IPT prefers AMP while plant IPT prefers ADP or ATP.</p> Signup and view all the answers

    What is T-DNA in the context of Agrobacterium tumefaciens?

    <p>A transfer DNA segment that integrates into the plant genome</p> Signup and view all the answers

    Which of the following growths is typically associated with the presence of Agrobacterium tumefaciens?

    <p>Crown gall</p> Signup and view all the answers

    What is the primary consequence of the interaction between Agrobacterium tumefaciens and plant cells?

    <p>Production of auxin and cytokinin leading to tumors</p> Signup and view all the answers

    Study Notes

    Agrobacterium tumefaciens and Crown Gall Disease

    • Agrobacterium tumefaciens causes crown gall disease in plants, characterized by tumor-like growths.
    • This bacterium induces the plant to produce auxin and cytokinin, plant hormones that stimulate cell division and growth.

    T-DNA Transfer and Tumor Formation

    • Agrobacterium tumefaciens carries Ti plasmids, which contain a segment of DNA called T-DNA.
    • This T-DNA is transferred into the plant nucleus, integrating into the plant genome.
    • The T-DNA includes genes for the biosynthesis of auxin and cytokinin, contributing to tumor formation.

    Cytokinin Biosynthesis and the tmr Gene

    • The tmr gene, present in T-DNA, encodes isopentenyl transferase, a key enzyme in cytokinin synthesis.
    • This enzyme converts AMP into isopentenyladenine (iP), a precursor for various cytokinins.

    Cytokinin Translocation and Vascular Cambium Activity

    • Cytokinin transport occurs via phloem and xylem, with different cytokinins being transported in each.
    • The xylem sap primarily carries trans-zeatin (tZ) and tZ riboside, produced in the roots by CYP735A.
    • Cytokinins play a crucial role in vascular cambium activity, contributing to secondary growth.
    • Grafting experiments with wild-type and ipt1;3;5;7 mutant plants reveal the long-distance translocation of CKs and their importance for cambial activity.

    Cytokinin Signaling Mechanism

    • Cytokinin signaling is mediated by a two-component-like system, involving phosphorylation of proteins.
    • Receptors (AHKs), histidine phosphotransfer proteins (HPTs/AHPs), and response regulators (ARRs) are key players.
    • AHKs perceive cytokinin and autophosphorylate, transferring the phosphate group to HPTs, then to ARRs.
    • ARRs are response regulators that activate downstream genes and influence various developmental processes.

    Arabidopsis Cytokinin Signaling Pathway

    • Arabidopsis possesses three CK receptors: AHK2, AHK3, and AHK4 (identified as the wol and cre1 mutants).
    • These receptors act partially redundantly, with the triple mutant exhibiting a complete loss of CK response.

    HPTs/AHPs and Response Regulation

    • HPTs/AHPs shuttle between the cytoplasm and nucleus, relaying the phosphate signal.
    • These proteins are essential for CK signaling but show a degree of redundancy, as loss of one or two AHPs has little effect, while a triple mutant exhibits a short root phenotype characteristic of CK signaling defects.

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    Description

    Explore the role of Agrobacterium tumefaciens in inducing crown gall disease in plants. This quiz covers the mechanisms of T-DNA transfer, tumor formation, and the significance of cytokinins in plant pathology. Test your understanding of how plant hormones are influenced by this bacterium.

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