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  • Thus regardless of its specific function


    Thus, regardless of its specific function, PTC52 is associated with plastid activity. During arbuscular mycorrhizal symbiosis, elongated plastids, which are interconnected through thin, tubular plastid projections called stromules, proliferate in arbuscule-containing root cortex cells (Fester et al., 2001; Hans et al., 2004; Lohse et al., 2005, 2006; Ivanov and Harrison, 2014). These changes in the shape of plastids are accompanied by specific modifications in their metabolism, some of which greatly influence arbuscular development and activity, including: C13/C14 apocarotenoid production (Strack and Fester, 2006); activation of the biosynthesis of plastic isoprenoid plant hormones such as gibberellins, 623 receptor and strigolactones (Fester, 2008; Takeda et al., 2015; Walter et al., 2015) and the plastid-located lipid-derived phytohormone jasmonate (Isayenkov et al., 2005; Hause and Schaarschmidt, 2009; Gutjahr et al., 2015). Recently, a comparative and quantitative proteomic analysis of AM and non-AM Medicago truncatula roots suggested that changes in plastid proteome and structure elicit a nutrient starvation signature that may prime arbuscule breakdown (Daher et al., 2017). In this study, we characterized a tomato Ptc52 gene inducible in roots and expressed in arbusculated cells during AM formation. SlPtc52 gene silencing led to a delay in colonization and a specific decrease in arbuscular abundance, thus suggesting that PTC52 plays a role in arbuscule formation. Unlike other plant Rieske-type oxygenase family members such as PAO, CAO and TIC55, Berim et al. (2014) have proposed that the PTC52 protein is a potential oxygenation catalyst in specialized plant metabolisms such as flavonoids. Its role during mycorrhization is still unknown, but we can speculate that could therefore be associated with its functional diversity in the context of specific modifications in plastid metabolism, oxidative protection and the generation of signalling compounds such as carotenoids and flavonoids.
    Acknowledgements We wish to thank the Tomato Genetics Resource Centre (TGRC) of the University of California for providing the tomato seeds. This study was supported by grants from the Interministerial Commission of Science and Technology (CICYT) and the European Regional Development Fund (FEDER) through the Spanish Ministry of the Economy and Competitiveness (AGL2014-52298-P; AGL2017-83871-P). J.A. Martín Rodríguez was supported by a research fellowship from the FPU-MICINN program. We also wish to thank Michael O’Shea for proofreading the manuscript.
    Introduction Heme oxygenase (HO) has two distinct isoforms: heme oxygenase-1 (HO-1), which is the inducible form, and heme oxygenase-2 (HO-2), which is the constitutive form [1,2]. HO-1 expression has been shown to be induced by oxidative stress, inflammatory cytokines, and heavy metals [3,4]. HO-2 is a 36-kDa protein that is constitutively expressed in most tissues [2]. There are many similarities between the mechanisms underlying heme oxidation in HO-1 and HO-2 in terms of co-factor and substrate specificity and susceptibility [4,5]. HO-2 activity has been shown to be critical for preventing seizure-related cerebral vascular injury in vivo and protecting against oxidative stress in vitro [6]. P Previous research has also shown that HO-2 is cytoprotective independently of its role in oxidative heme degradation [7]; ischemic injury and chronic inflammation are common in HO-2 null mice [8,9]. HO-2 plays an important role in inhibition of inflammatory responses [10], and HO-2 knockout mice display higher inflammatory cytokine levels and deficiencies in wound healing [11,12]. Overexpression of HO-2 inhibits lipopolysaccharide (LPS)-induced inflammatory responses in murine cerebral vascular endothelial cells, while RNAi-mediated depletion of HO-2 enhances these responses [13]. HO-2 is also expressed in macrophages, macrophage, it plays a role in decreasing inflammation to promote tissue healing and tissue repair [14]. HO-2 deletion impairs macrophage function, expression of HO-2 in the corneal epithelial is a key for the resolution and repaired for wound healing [15].