AUTHOR=Aung May Sann , Masuda Hiroshi 

TITLE=How Does Rice Defend Against Excess Iron?: Physiological and Molecular Mechanisms

JOURNAL=Frontiers in Plant Science

VOLUME=Volume 11 - 2020

YEAR=2020

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.01102

DOI=10.3389/fpls.2020.01102

ISSN=1664-462X

ABSTRACT=Iron (Fe) is an essential nutrient for all living organisms but can lead to cytotoxicity when present in excess. Fe toxicity often occurs in rice grown in submerged paddy fields with low pH, disrupting cell homeostasis and impairing growth and yield. However, the molecular mechanisms of Fe toxicity tolerance in plants are unclear. Microarray and genome-wide association analyses have shown that rice employs four defense systems to regulate Fe homeostasis under Fe excess. In defense 1, Fe excess tolerance is implemented by Fe exclusion as a result of suppression of genes involved in Fe uptake and translocation such as OsIRT1, OsYSL2, OsYSL15, OsNRAMP1, OsNAS1, OsNAS2, OsNAAT1, OsDMAS1, and OsTOM1. HRZ Fe-binding ubiquitin ligases regulate Fe uptake genes under Fe excess. In defense 2, rice includes and retains Fe in the root system rather than transporting it to shoots. In defense 3, rice compartmentalizes Fe in the shoot. In defense 2 and 3, the vacuolar Fe transporter OsVIT2, Fe storage protein ferritin, and the nicotinamine synthase OsNAS3 mediate the isolation or detoxification of excess Fe. In defense 4, rice detoxifies the ROS produced in response to excess Fe. Some OsWRKY transcription factors, S-nitrosoglutathione-reductase variants, p450-family proteins, and OsNAC4, 5, and 6 are implicated in defense 4. Our findings will facilitate the breeding of tolerant crops with increased productivity in low-pH, Fe-rich soils.