IbOr Regulates Photosynthesis under Heat Stress by Stabilizing IbPsbP in Sweetpotato

Abstract

The Orange (Or) protein regulates carotenoid biosynthesis and environmental stress in plants. Previously, we reported that overexpression of the sweetpotato [Ipomoea batatas (L.) Lam] Or gene (IbOr) in transgenic Arabidopsis (referred to as IbOr-OX/At) increased the efficiency of photosystem II (PSII) and chlorophyll content after heat shock. However, little is known about the role of IbOr in PSII-mediated protection against abiotic stress. In this study, comparative proteomics revealed that expression of PsbP (an extrinsic subunit of PSII) is up-regulated in heat-treated IbOr-OX/At plants. We then identified and functionally characterized the PsbP-like gene (IbPsbP) from sweetpotato. IbPsbP is predominantly localized in chloroplast, and its transcripts are tissue-specifically expressed and up-regulated in response to abiotic stress. In addition, IbOr interacts with IbPsbP and protects it from heat-induced denaturation, consistent with the observation that transgenic sweetpotato overexpressing IbOr maintained higher PSII efficiency and chlorophyll content upon exposure to heat stress. These results indicate that IbOr can protect plants from environmental stress not only by controlling carotenoid biosynthesis but also by directly stabilizing PSII.

Sensitivity and Responses of Chloroplasts to Heat Stress in Plants

“…The Orange (Or) protein functions as a holdase chaperone and regulates carotenoid biosynthesis and environmental stress in plants (Zhou et al, 2015;Park et al, 2016;Kang et al, 2017). After heat shock, the efficiency of PSII and chlorophyll contents are improved by the overexpression of the Or gene (IbOr) from Ipomoea batatas (L.) Lam in transgenic Arabidopsis (Park et al, 2016;Kang et al, 2017). In higher plants, oxygenevolving enhancer protein 2-1 (PsbP) protein is necessary for normal thylakoid structure.…”

“…PsbP can also regulate and stabilize the PSII (Yi et al, 2007(Yi et al, , 2009). Sweet potato plants can acquire heat tolerance by stabilizing IbPsbP using the holdase chaperone function of IbOr and stabilizing PSII (Kang et al, 2017). Collectively, chloroplast HSPs and other protein chaperones play important roles in acquiring thermtolerance and protecting chloroplast development and photosynthesis under heat stress.…”

Characterization of Cauliflower OR Mutant Variants

“…While ectopic expression of a wild-type OR gene increases carotenoid level (Bai et al, 2016;Park et al, 2016;Berman et al, 2017), likely due to its posttranslational upregulation of PSY protein level and activity, expression of either cauliflower OR mutant allele or an OR variant mimicking the "golden SNP" present in melon greatly promotes carotenoid accumulation in a number of plant species (Lopez et al, 2008;Yuan et al, 2015a;Kim et al, 2019;Yazdani et al, 2019). Interestingly, OR was recently found to regulate chloroplast biogenesis (Sun et al, 2019) and the expression of wild-type OR in sweetpotato and Arabidopsis lines enhances plant resistance to heat and oxidative stress treatments (Park et al, 2016;Kang et al, 2017;Kim et al, 2019).…”

Isolation, expression and function analysis of a bZIP transcription factor IbbZIP37 in sweetpotato (Ipomoea batatas L. [Lam])

“…The expression and function of genes regulating abiotic stress responses in sweeetpotato are of considerable interest. To date, several important stress-related genes, including IbLCY-β (Kim et al, 2014), IbOr (Sun et al, 2013;Goo et al, 2015;Kang et al, 2017b), IbPsbP (Kang et al, 2017b), IbCHY-β (Kang et al, 2017a), IbCBF3 (Jin et al, 2017), IbMPK3 and IbMPK6 (Kim et al, 2016) genes have been coloned from sweetpotato and functionally characterized in our laboratory. Previously, some bZIP genes have been reported with roles in response to abiotic stresses.…”