What Are The Specific Transcriptional Changes In The Arabidopsis Thaliana WRKY Transcription Factor Family That Occur In Response To Inoculation With The Necrotrophic Fungus Botrytis Cinerea, And How Do These Changes Impact The Regulation Of Salicylic Acid-mediated Defense Pathways To Prevent Fungal Penetration Of Plant Tissues?

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When Arabidopsis thaliana is inoculated with the necrotrophic fungus Botrytis cinerea, specific WRKY transcription factors are transcriptionally activated, playing crucial roles in the plant's defense response. Key findings include:

  1. Activation of WRKY Transcription Factors:

    • WRKY33 is significantly upregulated in response to Botrytis infection. It is influenced by both salicylic acid (SA) and jasmonic acid (JA) pathways, highlighting its role in coordinating defense responses.
    • WRKY70 is also induced and is particularly associated with SA-mediated defense pathways, contributing to the activation of downstream defense genes.

  2. Regulation of Defense Pathways:

    • These WRKY factors bind to W-box elements in the promoters of target genes, activating their expression. Notably, they induce genes such as PR-1, which are critical for producing pathogenesis-related proteins.

  3. Mechanisms of Defense:

    • The activation of SA-mediated pathways leads to the production of physical barriers, including lignification and callose deposition, which strengthen plant cell walls against fungal penetration.
    • The induction of antimicrobial compounds like camalexin further inhibits fungal growth, providing a toxic environment for the pathogen.

  4. Impact on Fungal Penetration:

    • The coordinated action of these WRKY factors results in the activation of defense mechanisms that impede Botrytis penetration. This includes both physical reinforcement of cell walls and the production of antimicrobial substances, effectively slowing fungal invasion and allowing the plant to mount a robust defense.

In summary, the transcriptional activation of WRKY33 and WRKY70 in response to Botrytis cinerea triggers a cascade of SA-mediated defense responses, enhancing the plant's ability to prevent fungal penetration through the production of defensive compounds and cell wall reinforcements.