Physiological and proteomic analyses of Tunisian local grapevine (Vitis vinifera) cultivar Razegui in response to drought stress.

Drought is one of the major environmental constraints threatening viticulture worldwide. Therefore, it is critical to reveal the molecular mechanisms underlying grapevine (Vitis vinifera L.) drought stress tolerance useful to select new species with higher tolerance/resilience potentials. Drought-tolerant Tunisian local grapevine cultivar Razegui was exposed to water deficit for 16days. Subsequent proteomic analysis revealed 49 differentially accumulated proteins in leaves harvested on the drought-stressed vines. These proteins were mainly involved in photosynthesis, stress defence, energy and carbohydrate metabolism, protein synthesis/turnover and amino acid metabolism. Physiological analysis revealed that reduction of photosynthesis under drought stress was attributed to the downregulation of the light-dependent reactions, Calvin cycle and key enzymes of the photorespiration pathway. The accumulation of proteins involved in energy and carbohydrate metabolism indicate enhanced need of energy during active stress acclimation. Accumulation of protein amino acids seems to play a protective role under drought stress due to their osmoprotectant and ROS scavenging potential. Reduced protein synthesis and turnover help plants preserving energy to fight drought stress. Proteins related to stress defence might scavenge ROS and transmit the ROS signal as an oxidative signal transducer in drought-stress signalling. All of these original results represent valuable information towards improving drought tolerance of grapevine and promoting sustainable viticulture under climate change conditions.

Proteomic responses in shoots of the facultative halophyte Aeluropus littoralis (Poaceae) under NaCl salt stress.

Salinity is an environmental constraint that limits agricultural productivity worldwide. Studies on the halophytes provide valuable information to describe the physiological and molecular mechanisms of salinity tolerance. Therefore, because of genetic relationships of Aeluropus littoralis (Willd) Parl. with rice, wheat and barley, the present study was conducted to investigate changes in shoot proteome patterns in response to different salt treatments using proteomic methods. To examine the effect of salinity on A. littoralis proteome pattern, salt treatments (0, 200 and 400mM NaCl) were applied for 24h and 7 and 30 days. After 24h and 7 days exposure to salt treatments, seedlings were fresh and green, but after 30 days, severe chlorosis was established in old leaves of 400mM NaCl-salt treated plants. Comparative proteomic analysis of the leaves revealed that the relative abundance of 95 and 120 proteins was significantly altered in 200 and 400mM NaCl treated plants respectively. Mass spectrometry-based identification was successful for 66 out of 98 selected protein spots. These proteins were mainly involved in carbohydrate, energy, amino acids and protein metabolisms, photosynthesis, detoxification, oxidative stress, translation, transcription and signal transduction. These results suggest that the reduction of proteins related to photosynthesis and induction of proteins involved in glycolysis, tricarboxylic acid (TCA) cycle, and energy metabolism could be the main mechanisms for salt tolerance in A. littoralis. This study provides important information about salt tolerance, and a framework for further functional studies on the identified proteins in A. littoralis.

Putative involvement of Thioredoxin h in early response to gravitropic stimulation of poplar stems.

Gravity perception and gravitropic response are essential for plant development. In herbaceous species, it is widely accepted that one of the primary events in gravity perception involves the displacement of amyloplasts within specialized cells. However, the early signaling events leading to stem reorientation are not fully known, especially in woody species in which primary and secondary growth occur. Thirty-six percent of the identified proteins that were differentially expressed after gravistimulation were established as potential Thioredoxin targets. In addition, Thioredoxin h expression was induced following gravistimulation. In situ immunolocalization indicated that Thioredoxin h protein co-localized with the amyloplasts located in the endodermal cells. These investigations suggest the involvement of Thioredoxin h in the first events of signal transduction in inclined poplar stems, leading to reaction wood formation.

Insight into the role of sugars in bud burst under light in the rose.

Bud burst is a decisive process in plant architecture that requires light in Rosa sp. This light effect was correlated with stimulation of sugar transport and metabolism in favor of bud outgrowth. We investigated whether sugars could act as signaling entities in the light-mediated regulation of vacuolar invertases and bud burst. Full-length cDNAs encoding two vacuolar invertases (RhVI1 and RhVI2) were isolated from buds. Unlike RhVI2, RhVI1 was preferentially expressed in bursting buds, and was up-regulated in buds of beheaded plants exposed to light. To assess the importance of sugars in this process, the expression of RhVI1 and RhVI2 and the total vacuolar invertase activity were further characterized in buds cultured in vitro on 100 mM sucrose or mannitol under light or in darkness for 48 h. Unlike mannitol, sucrose promoted the stimulatory effect of light on both RhVI1 expression and vacuolar invertase activity. This up-regulation of RhVI1 was rapid (after 6 h incubation) and was induced by as little as 10 mM sucrose or fructose. No effect of glucose was found. Interestingly, both 30 mM palatinose (a non-metabolizable sucrose analog) and 5 mM psicose (a non-metabolizable fructose analog) promoted the light-induced expression of RhVI1 and total vacuolar invertase activity. Sucrose, fructose, palatinose and psicose all promoted bursting of in vitro cultured buds under light. These findings indicate that soluble sugars contribute to the light effect on bud burst and vacuolar invertases, and can function as signaling entities.

Proteome analysis of apical and basal regions of poplar stems under gravitropic stimulation.

Gravity is a constant force guiding the direction of plant growth. In young poplar stem, reorientation of the apical region is mainly obtained by differential growth of elongating primary tissues. At the base, where elongation is achieved but where the cambium is active, reorientation is due to asymmetrical formation of reaction wood. After 45 min of gravistimulation, the stem showed no reorientation, but 1 week later, reaction wood was observed at the base of the stem. To determine the molecular mechanisms taking place at the top and base of the stem, after 45 min or 1 week of inclination, the changes induced in protein accumulation were studied by two-dimensional polyacrylamide gel electrophoresis and quantitatively analyzed using image analysis software. Around 300 protein spots were reproducibly detected and analyzed. Forty percent of these proteins showed significant changes after inclination. Mass spectrometry analysis of 135 spots led to the identification of 60 proteins involved in a wide range of activities and metabolisms. Very different patterns of protein expression were obtained according to conditions tested, highlighting the complexity of gravitropic responses. Our results suggest that primary and secondary tissues present specific mechanisms to sense reorientation and to respond to inclination. Some selected proteins are discussed.

Characterization and expression analysis under bending and other abiotic factors of PtaZFP2, a poplar gene encoding a Cys2/His2 zinc finger protein.

In plants, mechanoperception and transduction of mechanical signals have been studied essentially in Arabidopsis thaliana L. and Lycopersicon esculentum L. plants, i.e., in nonwoody plants. Here, we have described the isolation of both the full-length cDNA and the regulatory region of PtaZFP2, encoding a member of Cys2/His2 zinc finger protein (ZFP) family in Populus tremula L. x Populus alba L. Time course analysis of expression demonstrated that PtaZFP2 mRNA accumulated as early as 5 min in response to a controlled stem bending and is restricted to the organ where the mechanical stimulus is applied. The real-time quantitative Reverse Transcriptase Polymerase Chain Reaction experiments showed that PtaZFP2 was also rapidly up-regulated in poplar stems in response to gravitropism suggesting that PtaZFP2 is induced by different mechanical signals. Abundance of PtaZFP2 transcripts also increased highly in response to wounding and to a weaker extent to salt treatment and cold, which is consistent with the numerous putative cis-elements found in its regulatory region. As in other species, these data suggest that Cys2/His2 ZFPs could function in poplar as key transcriptional regulators in the acclimation response to different environmental factors.