Beschreibung:
<jats:title>Summary</jats:title><jats:p>
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<jats:list-item><jats:p>The photoreceptor phytochrome A acts as a light‐dependent molecular switch and regulates responses initiated by very low fluences of light (<jats:styled-content style="fixed-case">VLFR</jats:styled-content>) and high fluences (<jats:styled-content style="fixed-case">HIR</jats:styled-content>) of far‐red light. PhyA is expressed ubiquitously, but how phyA signaling is orchestrated to regulate photomorphogenesis is poorly understood.</jats:p></jats:list-item>
<jats:list-item><jats:p>To address this issue, we generated transgenic <jats:italic>Arabidopsis thaliana phyA‐201</jats:italic> mutant lines expressing the biologically active phyA‐<jats:styled-content style="fixed-case">YFP</jats:styled-content> photoreceptor in different tissues, and analyzed the expression of several reporter genes, including <jats:italic>ProHY5:<jats:styled-content style="fixed-case">HY</jats:styled-content>5‐<jats:styled-content style="fixed-case">GFP</jats:styled-content></jats:italic> and <jats:italic>Pro35S:<jats:styled-content style="fixed-case">CFP</jats:styled-content>‐<jats:styled-content style="fixed-case">PIF</jats:styled-content>1</jats:italic>, and various <jats:styled-content style="fixed-case">FR</jats:styled-content>‐<jats:styled-content style="fixed-case">HIR</jats:styled-content>‐dependent physiological responses.</jats:p></jats:list-item>
<jats:list-item><jats:p>We show that phyA action in one tissue is critical and sufficient to regulate flowering time and root growth; control of cotyledon and hypocotyl growth requires simultaneous phyA activity in different tissues; and changes detected in the expression of reporters are not restricted to phyA‐containing cells.</jats:p></jats:list-item>
<jats:list-item><jats:p>We conclude that <jats:styled-content style="fixed-case">FR</jats:styled-content>‐<jats:styled-content style="fixed-case">HIR</jats:styled-content>‐controlled morphogenesis in Arabidopsis is mediated partly by tissue‐specific and partly by intercellular signaling initiated by phyA. Intercellular signaling is critical for many <jats:styled-content style="fixed-case">FR</jats:styled-content>‐<jats:styled-content style="fixed-case">HIR</jats:styled-content> induced responses, yet it appears that phyA modulates the abundance and activity of key regulatory transcription factors in a tissue‐autonomous fashion.</jats:p></jats:list-item>
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