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The plant-specific COST1 protein balances plant growth and drought tolerance via attenuation of autophagy

ABSTRACT: Plants balance their conflicting requirements for growth and stress tolerance via sophisticated pathways and unique genes that control responses to the external environment. We have identified a novel plant-specific gene, COST1(Constitutively Stressed 1), that affects plant growth and negatively regulates drought resistance by manipulating the autophagy pathway. An Arabidopsis cost1 mutant has decreased growth and increased drought tolerance, together with constitutive autophagy and increased expression of drought-response genes. The COST1 protein is degraded upon plant dehydration, and this degradation is blocked by treatment with inhibitors of the 26S proteasome or autophagy pathways. The cost1 mutant drought resistance is dependent on an active autophagy pathway, indicating that COST1 acts through manipulation of autophagy. COST1 co-localizes to autophagosomes with the autophagosome marker ATG8e and the autophagy adaptor NBR1, and physically interacts with ATG8e, indicating a pivotal role in direct regulation of autophagy. We propose a model in which COST1 represses autophagy under optimal conditions, thus allowing plant growth. During drought, COST1 is degraded, enabling activation of autophagy and suppressing growth to enhance drought tolerance.

ORGANISM(S): Arabidopsis thaliana

PROVIDER: GSE113515 | GEO | 2020/04/16

REPOSITORIES: GEO

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Project description:Autophagy involvement in plant response to nitrogen, carbon and sulfur starvation was already reported, however the mechanisms responsible for its regulation and selectivity in such conditions were not yet investigated. We observed increased amounts of NBR1 transcript in plants exposed to sulfur deficit as compared to the control plants grown in nutrient sufficient conditions. This observation prompted us to investigate the role of this selective autophagy cargo receptor in plant response to sulfur deficit. Transcriptome analysis of the wild type and NBR overexpressing plants revealed differences in gene expression changes in response to sulfur deficit. Moreover, NBR1 overexpressors have significantly shorter roots than WT, when grown in nutrient deficient conditions in the presence of TOR kinase inhibitors, namely in the conditions leading to autophagy induction. Besides, NBR1 overexpression promoted stomata closure while NBR1 depletion stomata opening. Surprisingly, all lines had more closed stomata when grown in sulfur deficient than sulfur optimal conditions, what indicates that this effect is independent from NBR1. Similarly, ABA-dependent stomatal closure was independent from NBR1 and growth conditions. Cysteine also promoted stomatal closure in NBR1-independent way in plants grown in the optimal medium but in contrast, reduced the number of open stomata in plants from sulfur deficient medium. Interaction network analysis of the proteins co-purifying with NBR1 revealed links with proteins involved in degradation systems, and endosomal trafficking and a surprizing connection with nuclear transport. In addition, several proteins co-purifying with NBR1 were found only in sulfur deficient conditions. One of them, ribosomal protein S6 (RPS6) was further confirmed as a direct NBR1 interactor. Localization of the RPS6 interaction sites in NBR1 indicated that ubiquitin binding domain of NBR1 is not required for this interaction what means that it is rather not the classical “ubiquitinated target - autophagy receptor” interaction.

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The plant-specific COST1 protein balances plant growth and drought tolerance via attenuation of autophagy

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