Abstract
Multivesicular body (MVB)-mediated endosomal sorting and macroautophagy are the main pathways mediating the transport of cellular components to the vacuole and are essential for maintaining cellular homeostasis. The interplay of these two pathways remains poorly understood in plants. In this study, we show that FYVE DOMAIN PROTEIN REQUIRED FOR ENDOSOMAL SORTING 1 (FREE1), which was previously identified as a plant-specific component of the endosomal sorting complex required for transport (ESCRT), essential for MVB biogenesis and plant growth, can be transported to the vacuole for degradation in response to iron deficiency. The vacuolar transport of ubiquitinated FREE1 protein is mediated by the autophagy pathway. As a consequence, the autophagy deficient mutants, atg5-1 and atg7-2, accumulate more endogenous FREE1 protein and display hypersensitivity to iron deficiency. Furthermore, under iron-deficient growth condition autophagy related genes are upregulated to promote the autophagic degradation of FREE1, thereby possibly relieving the repressive effect of FREE1 on iron absorption. Collectively, our findings demonstrate a unique regulatory mode of protein turnover of the ESCRT machinery through the autophagy pathway to respond to iron deficiency in plants.
Highlights
Owing to a complex living environment, plants are habitually faced with various hostile situations, especially from multifarious abiotic and biotic stresses
We found that the endosomal sorting complex required for transport (ESCRT) component FREE1 could be degraded through the autophagy pathway
We and others showed that SINATs E3 ligases could modulate the ubiquitination and degradation of FREE1 protein to relieve its inhibitory effect on metal absorption or to adapt to other stressful growth conditions like plant recovery after ABA treatment [29,31,32]
Summary
Owing to a complex living environment, plants are habitually faced with various hostile situations, especially from multifarious abiotic and biotic stresses. The process of plant adaptation is usually accompanied by the elimination of harmful cellular components like denatured proteins and damaged organelles. The vacuolar system is an important and conserved pathway which is rich in acid hydrolases with functions in protein degradation. These hydrolases inside the vacuole degrade proteins and organelles which are transported to the vacuole through various membrane trafficking pathways [3,4]. Cytoplasmic components like protein aggregates or damaged organelles can be enveloped by a double-membrane structure termed the autophagosome and delivered to the vacuole through the macroautophagy pathway (hereafter referred to as autophagy) [5,6,7]. The external membrane of the autophagosome fuses with the tonoplast, whereby the cargoes enveloped by the inner membrane are released as the autophagic bodies to the vacuolar lumen, the inside cargo is degraded by various hydrolases for recycling [1,8]
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