Abstract
Abiotic stress is one of the major threats to plant crop yield and productivity. When plants are exposed to stress, production of reactive oxygen species (ROS) increases, which could lead to extensive cellular damage and hence crop loss. During evolution, plants have acquired antioxidant defense systems which can not only detoxify ROS but also adjust ROS levels required for proper cell signaling. Ascorbate peroxidase (APX), glutathione peroxidase (GPX), catalase (CAT) and superoxide dismutase (SOD) are crucial enzymes involved in ROS detoxification. In this study, 40 putative APX, 28 GPX, 16 CAT, and 41 SOD genes were identified from genomes of the resurrection species Boea hygrometrica, Selaginella lepidophylla, Xerophyta viscosa, and Oropetium thomaeum, and the mesophile Selaginella moellendorffii. Phylogenetic analyses classified the APX, GPX, and SOD proteins into five clades each, and CAT proteins into three clades. Using co-expression network analysis, various regulatory modules were discovered, mainly involving glutathione, that likely work together to maintain ROS homeostasis upon desiccation stress in resurrection species. These regulatory modules also support the existence of species-specific ROS detoxification systems. The results suggest molecular pathways that regulate ROS in resurrection species and the role of APX, GPX, CAT and SOD genes in resurrection species during stress.
Highlights
Being sessile organisms, plants have to live in continuously changing environments which are often hostile for their growth and development
Using similarity and Hidden Markov Model (HMM) based searches, we identified a total of 40 ascorbate peroxidase (APX),U28siGngPXsi,m16ilaCrAitTy aanndd 4H1iSdOdeDngMenaerskionvthMeogdeenlo(mHeMs Mof)thbeasfeodursreeasruchrreesc,tiwone aidnedntthifieeddesaictcoatatiloonf s4e0nAsiPtiXve, 2s8pGecPiXes,.16ThCeAsTe ainndcl4u1dSedODfivgeenAesPiXn,thneingeenGoPmXe,s othfrtehee fCoAuTr reasnudrrescetvioenn aSnOdDthegedneessicciantioBn. hsyegnrsoimtivetersicpae,ceieigs.hTt hAePsXe i,nfcivluedGedPXfiv, ethArPeeXC, nAinTeaGnPdXe,itghhret eSCOADT gaenndessevinenOS.OthDomgeaneuems i,n1B1
Two different approaches were used for the genome-wide identification of APX, glutathione peroxidase (GPX), CAT and superoxide dismutase (SOD) genes: (i) the APX, GPX, CAT and SOD protein sequences of Arabidopsis were retrieved from the UniProtKB database and searched against the deduced protein sequences of predicted gene models using blastp (1E-20; v2.2.29+). (ii) HMM profiles of the domains corresponding to APXs (PF00141), GPXs (PF00255), SODs (PF00080; PF00081; PF02777) and CATs (PF00199) were downloaded from the Pfam database and scanned against the deduced protein sequences of the five species analyzed here, using HMMER v3.1b2 [75] with an E-value cutoff of 1E-10
Summary
Plants have to live in continuously changing environments which are often hostile for their growth and development These environmental conditions include biotic stresses due to pathogen or herbivore attack, and abiotic stresses due to water shortage (drought), salinity, cold, heat, and others. A manifold antioxidant system evolved in plants allowing combating the cellular damages otherwise caused by ROS, and to fine-tune the low levels of ROS required for cell signaling. This antioxidant defense system includes both enzymatic and non-enzymatic components, where ascorbate peroxidase (APX), glutathione peroxidase (GPX), catalase (CAT), and superoxide dismutase (SOD) constitute the main enzymatic classes [1,2].
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