RESUMEN
The origin and evolution of land plants was an important event in the history of life and initiated the establishment of modern terrestrial ecosystems. From water to terrestrial environments, plants needed to overcome the enhanced ultraviolet (UV) radiation and many other DNA-damaging agents. Evolving new genes with the function of DNA repair is critical for the origin and radiation of land plants. In bacteria, the DNA-3-methyladenine glycosylase (MAG) recognizes of a variety of base lesions and initiates the process of the base excision repair for damaged DNA. The homologs of MAG gene are present in all major lineages of streptophytes, and both the phylogenic and sequence similarity analyses revealed that green plant MAG gene originated through an ancient horizontal gene transfer (HGT) event from bacteria. Experimental evidence demonstrated that the expression of the maize ZmMAG gene was induced by UV and zeocin, both of which are known as DNA-damaging agents. Further investigation revealed that Streptophyta MAG genes had undergone positive selection during the initial evolutionary period in the ancestor of land plants. Our findings demonstrated that the ancient HGT of MAG to the ancestor of land plants probably played an important role in preadaptation to DNA-damaging agents in terrestrial environments.
Asunto(s)
Bacterias/enzimología , Bacterias/genética , ADN Glicosilasas/genética , Transferencia de Gen Horizontal , Streptophyta/enzimología , Streptophyta/genética , Evolución Molecular , Homología de SecuenciaRESUMEN
Previously, it was reported that like land plants, the green alga Klebsormidium flaccidum (Streptophyta) accumulates sucrose during cold acclimation (Nagao et al. Plant Cell Environ 31:872-885, 2008), suggesting that synthesis of sucrose could enhance the freezing tolerance of this alga. Because sucrose phosphate phosphatase (SPP; EC 3.1.3.24) is a key enzyme in the sucrose synthesis pathway in plants, we analyzed the SPP gene in K. flaccidum (KfSPP, GenBank accession number AB669024) to clarify its role in sucrose accumulation. As determined from its deduced amino acid sequence, KfSPP contains the N-terminal domain that is characteristic of the L-2-haloacid-dehalogenase family of phosphatases/hydrolases (the HAD phosphatase domain). However, it lacks the extensive C-terminal domain found in SPPs of land plants. Database searches revealed that the SPPs in cyanobacteria also lack the C-terminal domain. In addition, the green alga Coccomyxa (Chlorophyta) and K. flaccidum, which are closely related to land plants, have cyanobacterial-type SPPs, while Chlorella (Chlorophyta) has a land plant-type SPP. These results demonstrate that even K. flaccidum (Streptophyta), as a recent ancestor of land plants, has the cyanobacterial-type SPP lacking the C-terminal domain. Because SPP and sucrose phosphate synthase (SPS) catalyze sequential reactions in sucrose synthesis in green plant cells and the lack of the C-terminal domain in KfSPP is predicted to decrease its activity, the interaction between decreased KfSPP activity and SPS activity may alter sucrose synthesis during cold acclimation in K. flaccidum.
Asunto(s)
Monoéster Fosfórico Hidrolasas/metabolismo , Plantas/enzimología , Streptophyta/enzimología , Sacarosa/metabolismo , Secuencia de Aminoácidos , Cianobacterias/enzimología , Cianobacterias/genética , Evolución Molecular , Regulación Enzimológica de la Expresión Génica , Genes de Plantas , Datos de Secuencia Molecular , Monoéster Fosfórico Hidrolasas/genética , Reguladores del Crecimiento de las Plantas/genética , Plantas/genética , Plantas/metabolismo , Estructura Terciaria de Proteína , Streptophyta/genética , Streptophyta/metabolismoRESUMEN
Molecular phylogenetic analyses of 93 new and 198 non-redundant GenBank rbcL sequences of the family Desmidiaceae (Zygnematophyceae, Streptophyta) established 22 mostly highly supported clades, in addition to four non-supported lineages and eight single-taxon branches within the family. Nine novel clades and single-taxon branches were identified, suggesting that current taxon sampling has not reached saturation in the family. The highly polyphyletic nature of most desmid genera corroborated in this study using a large taxon set, calls for re-evaluation of the genus concept in the family Desmidiaceae that traditionally relied on features of cell morphology. Molecular phylogenetic data have shown that these morphological characters are highly homoplastic or plesiomorphic and thus cannot be used to delineate genera. The dramatic discrepancy between the currently practised systematic treatment of the family and the composition of the clades based on sequence comparisons requires emendation of almost all existing genera and description of a larger number of novel genera. The clades identified during this study provide a framework for the future emendation/description of genera in the Desmidiaceae.
Asunto(s)
Filogenia , Proteínas de Plantas/genética , Ribulosa-Bifosfato Carboxilasa/genética , Streptophyta/clasificación , Streptophyta/enzimología , Evolución Molecular , Datos de Secuencia Molecular , Análisis de Secuencia de ADN , Streptophyta/genéticaRESUMEN
The DI protein of photosystem II (PS II) complex of a microalga Chaetosphaeridium globosum has been theoretically modelled from its sequence using comparative modeling with known backbone structure of DI protein from bacterium Thermosynechococcus vulcanus as template. The model is built with missing loops and all side chains, which are not resolved in the structure of the template. The structure of the tetramanganese cluster (TMC) and the ligand forming side chains have been subjected to modeling studies in order to gather more information useful to understanding of the water splitting reactions. Earlier models of TMC have been scrutinized and an insight into the manganese coordination sphere has been provided.
