Cloning and expression analysis of an ADP-ribosylation factor from Solanum tuberosum L

Structure, organization and evolution of ADP-ribosylation factors in rice and foxtail millet, and their expression in rice

ADP-ribosylation factors (ARFs) have been reported to function in diverse physiological and molecular activities. Recent evidences also demonstrate the involvement of ARFs in conferring tolerance to biotic and abiotic stresses in plant species. In the present study, 23 and 25 ARF proteins were identified in C3 model- rice and C4 model- foxtail millet, respectively. These proteins are classified into four classes (I-IV) based on phylogenetic analysis, with ARFs in classes I-III and ARF-like proteins (ARLs) in class IV. Sequence alignment and domain analysis revealed the presence of conserved and additional motifs, which may contribute to neo- and sub-functionalization of these proteins. Promoter analysis showed the presence of several cis-regulatory elements related to stress and hormone response, indicating their role in stress regulatory network. Expression analysis of rice ARFs and ARLs in different tissues, stresses and abscisic acid treatment highlighted temporal and spatial diversification of gene expression. Five rice cultivars screened for allelic variations in OsARF genes showed the presence of allelic polymorphisms in few gene loci. Altogether, the study provides insights on characteristics of ARF/ARL genes in rice and foxtail millet, which could be deployed for further functional analysis to extrapolate their precise roles in abiotic stress responses.

Expression characteristics of ARF1 and SAR1 during development and the de-etiolation process

ARF1 (ADP-ribosylation factor 1) and SAR1 (secretion-associated RAS super family) are involved in the formation and budding of vesicles throughout plant endomembrane systems. The molecular mechanisms of this transport have been studied extensively in mammalian and yeast cells. However, very little is known about the mechanisms of coat protein complex (COP) formation and recruitment of COP-vesicle cargoes in plants. To provide insights into vesicular trafficking in Pisum sativum L., we investigated mRNA and protein expression patterns of ARF1 and SAR1 in roots and shoots at early growth stages and in the de-etiolation process. We showed that ARF1 was concentrated mostly in the crude Golgi fractions, and SAR1 was concentrated predominantly in the crude ER fractions of de-etiolated shoots. ARF1 and SAR1 proteins were several times more abundant in shoots relative to roots. In total protein homogenates, the expression level of SAR1 and ARF1 was higher in shoots of dark-grown pea plants than light-grown plants. In contrast, ARF1 was higher in roots of light-grown pea relative to roots of dark-grown pea. With ageing, the ARF1 mRNA in roots was reduced, while SAR1 expression increased. Unlike ARF1 transcripts, ARF1 protein levels did not fluctuate significantly in root and shoot tissue during early development. The relative abundance of SAR1 protein in root tissues may suggest a high level of vesicular transport from the ER to the Golgi. Experimental results suggested that white light probably affects the regulation of ARF1 and SAR1 protein levels. On the other hand, short-term white light affects SAR1 but not ARF1.

Identification and localization of a beta-COP-like protein involved in the morphodynamics of the plant Golgi apparatus

This paper examines the molecular machinery involved in membrane exchange within the plant endomembrane system. A study has been undertaken on beta-COP-like proteins in plant cells using M3A5, an antibody raised against the conserved sequence of mammalian beta-COP proteins. In mammalian cells, beta-COP proteins are part of a complex named the coatomer, which probably recruits some specific areas of the endomembrane system. Immunofluorescence analyses by confocal laser scanning microscopy showed that beta-COP-like proteins marked predominantly the plant Golgi apparatus. Other proteins known to be part of a potential machinery for COPI vesicle formation (gamma-COP, beta'-COP and Arf1 proteins) were immunolocalized on the same membraneous structures as beta-COP. Moreover, beta-COP and other COPI antibodies stained the cell plate in dividing cells. It is further shown that, in maize root cells, and in contrast to observations upon mammalian cells, the drug Brefeldin A (BFA) does not induce the release of beta-COP and Arf1 proteins from the Golgi membrane into the cytosol. These data clearly demonstrate that the antibody M3A5 is a valuable marker for studies on trafficking events in plant cells. They also report for the first time the location of COP components in plant tissue at the light level, especially on a model well known for secretion, i.e. the maize root cells. They also suggest that the membrane recruitment machinery may function in a plant-specific way.

Cloning and expression analyses of cDNA encoding an ADP-ribosylation factor from wheat: tissue-specific expression of wheat ARF

We isolated and characterized a cDNA clone encoding a small GTP-binding protein, which has a high similarity to mammalian ADP-ribosylation factor (ARF), from a cDNA library prepared from immature spikes of wheat (Triticum aestivum L.). The cDNA contained an open reading frame that encodes a polypeptide of 181 amino acids with a calculated molecular mass of 20.7 kDa. The deduced amino acid sequence showed a quite high homology to known ARFs from other organisms. In particular, the wheat ARF was completely identical to the rice ARF1. Genomic Southern hybridization suggested that wheat ARF is encoded by at least two or three copies of ARF genes. Northern analyses showed that the accumulation of the ARF transcripts was nearly constant throughout various environmental stresses in both shoots and roots. However the RNA transcript was preferentially expressed in roots rather than in shoots. A similar expression pattern was also observed at the protein level by Western analysis. The relative abundance of the ARF proteins in root and flower tissues may indicate a high level of vesicular transporting activity in the roots and flowers of wheat plants.