HSP90C interacts with PsbO1 and facilitates its thylakoid distribution from chloroplast stroma in Arabidopsis

Abstract

Arabidopsis plastidic HSP90C is an HSP90 family molecular chaperone that is required for chloroplast development and function. To understand the mechanism of action of HSP90C within the chloroplast, we conducted a yeast two-hybrid screening and revealed it interacts directly with the photosystem II extrinsic protein PsbO1, which performs a canonical function in the thylakoid lumen. To understand the biological significance of HSP90C-PsbO1 interaction, we investigated the role of HSP90C in modulating the stromal and thylakoid distribution of PsbO1GFP fusion protein. Fusion to GFP significantly delays the PsbO1 thylakoid transport and induces a variegation phenotype. Overexpression of HSP90C promotes the thylakoid distribution of PsbO1GFP and alleviates the leaf variegation. By tracking the chloroplast maturation during photomorphogenesis, we observed PsbO1GFP tends to form distinct fluorescent clusters within the stroma with delayed thylakoid membrane biogenesis, while HSP90C overexpression corrects these adverse effects. We also demonstrated that active HSP90C function is specifically required for stable accumulation of mature PsbO1GFP in thylakoid by using specific inhibitor geldanamycin. This study therefore not only identified novel HSP90C interactors, but also reports for the first time that PsbO1 enroute from the cytoplasm to thylakoid lumen is tightly regulated by the HSP90C chaperone complex in plastid stroma; whereas the proper HSP90C homeostasis is also critical for chloroplast maturation and function.

Plastid chaperone HSP90C guides precursor proteins to the SEC translocase for thylakoid transport

“…After stratification in the dark at 4 °C for 3–4 d, seeds were cultured within a plant growth incubator set at 120 μmol m −2 s −1 , 16/8 h light/dark cycle at 22 °C. Transgenic seedlings used were generated previously ( Oh et al , 2014 ; Jiang et al , 2017 ). The T7-tagged SecY1 (SCY1) line was previously described ( Skalitzky et al , 2011 ) and was kindly provided by Dr Donna Fernandez (University of Wisconsin, USA).…”

“…Additionally, DnaK (Hsp70), DnaJ (Hsp40), and GroEL/ES (Hsp60/Hsp10) have been directly implicated in the Sec pathway through interaction with SecB ( Phillips and Silhavy, 1990 ; Sakr et al , 2010 ; Calloni et al , 2012 ; Castanie-Cornet et al ., 2014 ). In the plant Arabidopsis, we recently identified a transient interaction between HSP90C and PsbO1, a nuclear-encoded thylakoid lumen subunit of the PSII complex ( Jiang et al , 2017 ). We showed that inhibiting HSP90C activity altered the distribution of the PsbO1–green fluorescent protein (GFP) fusion protein between the stroma and thylakoid compartments.…”

“…HSP90C has been shown to interact with components of the TOC–TIC, complex, and its ATPase activity has been implicated in chloroplast envelope protein import alongside HSP93 ( Inoue et al , 2013 ). As a molecular chaperone, HSP90C has been shown to regulate the function of other proteins such as PsbO1 ( Jiang et al , 2017 ) and VIPP1 post-translationally ( Feng et al , 2014 ). On the other hand, the chaperone’s own expression and accumulation are also developmentally regulated, and transgene-induced silencing caused impaired chloroplast development ( Oh et al , 2014 ) as well as accumulation of reactive oxygen species ( Islam et al , 2020 ).…”

Plastid Envelope-Localized Proteins Exhibit a Stochastic Spatiotemporal Relationship to Stromules

“…However, several plastidial proteins have been shown to localize as punctae or patches (Lee et al, 2001 ; Xu et al, 2005 ; Awai et al, 2006 ; Haswell and Meyerowitz, 2006 ; Seo et al, 2009 ; Tan et al, 2011 ; Liang et al, 2017 ; Li et al, 2017 ; Wang et al, 2017 ). While many of the reports have relied on transient protein over-expression in heterologous systems for their observations, stable transgenic lines that maintain a rather specific localization pattern for the fusion proteins, such as the poles of chloroplasts (Aranda-Sicilia et al, 2016 ), or clusters in the stroma (Jiang et al, 2017 ), have also been reported. We considered the possibility that stable transgenic lines that exhibit discrete fluorescent protein patches on the chloroplast envelope can serve as useful fiducial markers for assessing protein localization to different regions, including the extensions, of a chloroplast.…”

A novel role for PsbO1 in photosynthetic electron transport as suggested by its light-triggered selective nitration inArabidopsis thaliana

“…69 Arabidopsis plastidic heat shock protein 90 (Hsp90C) reportedly regulates the import of PsbO1 protein from the cytoplasm to thylakoid lumen. 72 How nitration of 9 Tyr of PsbO1 affects this regulation is not known. In addition, the fate of nitrated PsbO1 protein is an intriguing and important issue.…”