AUTHOR=Yang Chiu-Ling , Huang Yu-Ting , Schmidt Wolfgang , Klein Patricia , Chan Ming-Tsair , Pan I-Chun 

TITLE=Ethylene Response Factor109 Attunes Immunity, Photosynthesis, and Iron Homeostasis in Arabidopsis Leaves

JOURNAL=Frontiers in Plant Science

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.841366

DOI=10.3389/fpls.2022.841366

ISSN=1664-462X

ABSTRACT=<p>Iron (Fe) is an essential micronutrient element for all organisms including plants. Chlorosis of young leaves is a common symptom of Fe deficiency, reducing the efficiency of photosynthesis, and, ultimately, crop yield. Previous research revealed strong responsiveness of the putative key transcription factor <italic>ERF109</italic> to the Fe regime. To elucidate the possible role of <italic>ERF109</italic> in leaf Fe homeostasis and photosynthesis, we subjected <italic>Arabidopsis thaliana erf109</italic> knockout lines and Col-0 wild-type plants to transcriptome profiling <italic>via</italic> RNA-seq. The transcriptome profile of Fe-sufficient <italic>erf109</italic> leaves showed a 71% overlap with Fe-deficient Col-0 plants. On the other hand, genes that were differentially expressed between Fe-deficient and Fe-sufficient Col-0 plants remained unchanged in <italic>erf109</italic> plants under conditions of Fe deficiency. Mutations in <italic>ERF109</italic> increased the expression of the clade Ib bHLH proteins <italic>bHLH38</italic>, <italic>bHLH39</italic>, <italic>bHLH101</italic>, the nicotianamine synthase <italic>NAS4</italic>, and the Fe storage gene <italic>FER1</italic>. Moreover, mutations in <italic>ERF109</italic> led to significant down-regulation of defense genes, including <italic>CML37</italic>, <italic>WRKY40</italic>, <italic>ERF13</italic>, and <italic>EXO70B2</italic>. Leaves of <italic>erf109</italic> exhibited increased Fe levels under both Fe-sufficient and Fe-deficient conditions. Reduced Fv/Fm and Soil Plant Analysis Development (SPAD) values in <italic>erf109</italic> lines under Fe deficiency indicate curtailed ability of photosynthesis relative to the wild-type. Our findings suggest that <italic>ERF109</italic> is a negative regulator of the leaf response to Fe deficiency. It further appears that the function of <italic>ERF109</italic> in the Fe response is critical for regulating pathogen defense and photosynthetic efficiency. Taken together, our study reveals a novel function of <italic>ERF109</italic> and provides a systematic perspective on the intertwining of the immunity regulatory network and cellular Fe homeostasis.</p>