AUTHOR=Tran Lien Hong , Kim Jin-Gil , Jung Sunyo 

TITLE=Expression of the Arabidopsis Mg-chelatase H subunit alleviates iron deficiency-induced stress in transgenic rice

JOURNAL=Frontiers in Plant Science

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2023.1098808

DOI=10.3389/fpls.2023.1098808

ISSN=1664-462X

ABSTRACT=<p>The most common symptom of iron (Fe) deficiency in plants is leaf chlorosis caused by impairment of chlorophyll biosynthesis. Magnesium (Mg)-chelatase H subunit (CHLH) is a key component in both chlorophyll biosynthesis and plastid signaling, but its role in Fe deficiency is poorly understood. Heterologous expression of the <italic>Arabidopsis thaliana</italic> Mg-chelatase H subunit gene (<italic>AtCHLH</italic>) increased Mg-chelatase activity by up to 6-fold and abundance of its product, Mg-protoporphyrin IX (Mg-Proto IX), by 60–75% in transgenic rice (<italic>Oryza sativa</italic>) seedlings compared to wild-type (WT) controls. Noticeably, the transgenic seedlings showed alleviation of Fe deficiency symptoms, as evidenced by their less pronounced leaf chlorosis and lower declines in shoot growth, chlorophyll contents, and photosynthetic efficiency, as indicated by <italic>F</italic><sub>v</sub>/<italic>F</italic><sub>m</sub> and electron transport rate, compared to those in WT seedlings under Fe deficiency. Porphyrin metabolism was differentially regulated by Fe deficiency between WT and transgenic seedlings, particularly with a higher level of Mg-Proto IX in transgenic lines, showing that overexpression of <italic>AtCHLH</italic> reprograms porphyrin metabolism in transgenic rice. Leaves of Fe-deficient transgenic seedlings exhibited greater upregulation of deoxymugineic acid biosynthesis-related genes (i.e., <italic>NAS</italic>, <italic>NAS2</italic>, and <italic>NAAT1</italic>), <italic>YSL2</italic> transporter gene, and Fe-related transcription factor genes <italic>IRO2</italic> and <italic>IDEF2</italic> than those of WT, which may also partly contribute to alleviating Fe deficiency. Although <italic>At</italic>CHLH was postulated to act as a receptor for abscisic acid (ABA), exogenous ABA did not alter the phenotypes of Fe-deficient WT or transgenic seedlings. Our study demonstrates that modulation of porphyrin biosynthesis through expression of <italic>AtCHLH</italic> in transgenic rice alleviates Fe deficiency-induced stress, suggesting a possible role for CHLH in Fe deficiency responses.</p>