AUTHOR=Lin Li-Yen , Chow Hong-Xuan , Chen Chih-Hao , Mitsuda Nobutaka , Chou Wen-Chun , Liu Tzu-Yin 

TITLE=Role of autophagy-related proteins ATG8f and ATG8h in the maintenance of autophagic activity in Arabidopsis roots under phosphate starvation

JOURNAL=Frontiers in Plant Science

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2023.1018984

DOI=10.3389/fpls.2023.1018984

ISSN=1664-462X

ABSTRACT=<p>Nutrient starvation-induced autophagy is a conserved process in eukaryotes. Plants defective in autophagy show hypersensitivity to carbon and nitrogen limitation. However, the role of autophagy in plant phosphate (Pi) starvation response is relatively less explored. Among the core autophagy-related (<italic>ATG</italic>) genes, <italic>ATG8</italic> encodes a ubiquitin-like protein involved in autophagosome formation and selective cargo recruitment. The <italic>Arabidopsis thaliana ATG8</italic> genes, <italic>AtATG8f</italic> and <italic>AtATG8h</italic>, are notably induced in roots under low Pi. In this study, we show that such upregulation correlates with their promoter activities and can be suppressed in the <italic>phosphate response 1</italic> (<italic>phr1</italic>) mutant. Yeast one-hybrid analysis failed to attest the binding of the <italic>At</italic>PHR1 transcription factor to the promoter regions of <italic>AtATG8f</italic> and <italic>AtATG8h</italic>. Dual luciferase reporter assays in <italic>Arabidopsis</italic> mesophyll protoplasts also indicated that <italic>At</italic>PHR1 could not transactivate the expression of both genes. Loss of <italic>At</italic>ATG8f and <italic>At</italic>ATG8h leads to decreased root microsomal-enriched ATG8 but increased ATG8 lipidation. Moreover<italic>, atg8f/atg8h</italic> mutants exhibit reduced autophagic flux estimated by the vacuolar degradation of ATG8 in the Pi-limited root but maintain normal cellular Pi homeostasis with reduced number of lateral roots. While the expression patterns of <italic>AtATG8f</italic> and <italic>AtATG8h</italic> overlap in the root stele, <italic>AtATG8f</italic> is more strongly expressed in the root apex and root hair and remarkably at sites where lateral root primordia develop. We hypothesize that Pi starvation-induction of <italic>At</italic>ATG8f and <italic>At</italic>ATG8h may not directly contribute to Pi recycling but rely on a second wave of transcriptional activation triggered by PHR1 that fine-tunes cell type-specific autophagic activity.</p>