Acclimation to frost alters proteolytic response of wheat seedlings to drought

Identification of a novel endornavirus in Geranium carolinianum and occurrence within three agroecosystems

A putative endornavirus was detected in Carolina geranium (Geranium carolinianum) in Louisiana, USA. The virus was provisionally named Geranium carolinianum endornavirus 1 (GcEV1). The viral RNA was sequenced, and it consisted of 14,625 nt containing a single ORF coding a putative polyprotein of 4815 aa with conserved domains for a helicase 1, peptidase C97, glycosyl transferase GTB-type, and RNA-dependent RNA polymerase 2. The 5'end consisted of 130 nt while the 3'end consisted of 54 nt ending in nine cytosine residues. The closest relative to GcEV1 was Phaseolus vulgaris endornavirus 3. In phylogenetic analyses, GcEV1 clustered with members of the genus Alphaendornavirus. GcEV1 was detected in 57 of 60 G. carolinianum plants collected from three distinct agroecosystems. The virus was not detected in eight other species of the genus Geranium. There was no association of a particular phenotypic trait of the host with the presence or absence of the virus. GcEV1 was transmitted at a rate of 100% in seeds of a self-pollinated G. carolinianum plant.

Interactions of plant growth responses to spring freezing and summer drought: a multispecies comparison

PREMISE OF THE STUDY

Freezing and drought both result in cellular dehydration, and similar physiological responses to these stressors may result in cross acclimation, whereby prior freezing exposure increases subsequent drought tolerance. We examined how spring freezing influences summer drought tolerance for a range of herbaceous old field species: 6 graminoids (Agrostis stolonifera, Arrhenatherum elatius, Bromus inermis, Festuca rubra, Lolium perenne, Poa compressa) and 2 forbs (Plantago lanceolata, Securigera varia), with the goal of examining the generality of cross acclimation responses.

METHODS

We exposed the plants to -5°C in the spring and to a 3-week summer drought, and harvested the plants after a 3-week watering/recovery period. We also measured leaf soluble proteins and sugars to explore the potential mechanisms before and during drought stress.

KEY RESULTS

For Agrostis stolonifera, Bromus inermis, Lolium perenne, Plantago lanceolata, and Poa compressa there was evidence of cross acclimation based on aboveground or belowground biomass, with a reduction in the severity of the drought effect for the plants previously exposed to freezing. Freezing and drought effects were additive for Arrhenatherum elatius, and for the remaining two species the test of the freezing-drought interaction was inconclusive, because significant drought and freezing effects did not co-occur. When present, freezing-drought interactions were not correlated with changes in leaf soluble protein or sugars.

CONCLUSIONS

Our results reveal that the phenomenon of freezing-drought cross acclimation appears to be common in herbaceous species, and variation among species in cross acclimation indicates that multiple stresses could alter relative species abundances in plant communities.

Cysteine proteases and wheat (Triticum aestivum L) under drought: A still greatly unexplored association

Bread wheat (Triticum aestivum L.) provides about 19% of global dietary energy. Environmental stress, such as drought, affects wheat growth causing premature plant senescence and ultimately plant death. A plant response to drought is an increase in protease-mediated proteolysis with rapid degradation of proteins required for metabolic processes. Among the plant proteases that are increased in their activity following stress, cysteine proteases are the best characterized. Very little is known about particular wheat cysteine protease sequences, their expression and also localization. The current knowledge on wheat cysteine proteases belonging to the five clans (CA, CD, CE, CF and CP) is outlined, in particular their expression and possible function under drought. The first successes in establishing an annotated wheat genome database are further highlighted which has allowed more detailed mining of cysteine proteases. We also share our thoughts on future research directions considering the growing availability of genomic resources of this very important food crop. Finally, we also outline future application of developed knowledge in transgenic wheat plants for environmental stress protection and also as senescence markers to monitor wheat growth under environmental stress conditions.

Prior exposure to freezing stress enhances the survival and recovery of Poa pratensis exposed to severe drought

PREMISE OF THE STUDY

Both freezing and drought cause cellular dehydration, and they elicit similar increases in protective compounds, which suggests that these stresses could potentially interact. We examined whether the physiological changes that occur in response to freezing in the fall and spring could affect subsequent survival and growth after summer drought.

METHODS

We froze Poa pratensis tillers in the late fall, early spring, or late spring at 0, -5, or -10°C for 3 d and then subjected them to no drought (-0.025 MPa), moderate drought (-0.140 MPa), or severe drought (-0.250 MPa) for 3 wk in the summer. We quantified survival and total biomass after a 3-wk recovery period, and we determined leaf soluble sugar concentrations before and then 0, 30, and 55 d after freezing.

KEY RESULTS

For survival and biomass, there were significant interactions between freezing and drought. Spring frozen tillers had the highest biomass and survival following severe drought, whereas fall freezing did not significantly increase the biomass of tillers following the severe drought. Increased drought tolerance after spring freezing did not appear to be associated with increased soluble sugar content, given that the freezing effects on leaf glucose, fructose, and sucrose content were absent 55 d post freezing.

CONCLUSIONS

Our results demonstrate that multiple stresses that occur over different seasons can interact; this interaction is highly relevant to herbaceous species in northern temperate regions that are experiencing more intense and frequent stress as a result of changes in snow cover and extreme climatic events.

Maize proteomic responses to separate or overlapping soil drought and two-spotted spider mite stresses

In maize, leaf proteome responses evoked by soil drought applied separately differ from those evoked by mite feeding or both types of stresses occurring simultaneously. This study focuses on the involvement of proteomic changes in defence responses of a conventional maize cultivar (Bosman) to the two-spotted spider mite infestation, soil drought and both stresses coexisting for 6 days. Under watering cessation or mite feeding applied separately, the protein carbonylation was not directly linked to the antioxidant enzymes' activities. Protein carbonylation increased at higher and lower SOD, APX, GR, POX, PPO activities following soil drought and mite feeding, respectively. Combination of these stresses resulted in protein carbonylation decrease despite the increased activity of all antioxidant enzymes (except the CAT). However, maize protein network modification remains unknown upon biotic/abiotic stresses overlapping. Here, using multivariate chemometric methods, 94 leaf protein spots (out of 358 considered; 2-DE) were identified (LC-MS/MS) as differentiating the studied treatments. Only 43 of them had individual discrimination power. The soil drought increased abundance of leaf proteins related mainly to photosynthesis, carbohydrate metabolism, defence (molecular chaperons) and protection. On the contrary, mite feeding decreased the abundance of photosynthesis related proteins and enhanced the abundance of proteins protecting the mite-infested leaf against photoinhibition. The drought and mites occurring simultaneously increased abundance of proteins that may improve the efficiency of carbon fixation, as well as carbohydrate and amino acid metabolism. Furthermore, increased abundance of the Rubisco large subunit-binding protein (subunit β), fructose-bisphosphate aldolase and mitochondrial precursor of Mn-SOD and decreased abundance of the glycolysis-related enzymes in the mite-free leaf (in the vicinity of mite-infested leaf) illustrate the involvement of these proteins in systemic maize response to mite feeding.

A triticale water-deficit-inducible phytocystatin inhibits endogenous cysteine proteinases in vitro

Water-deficit is accompanied by an increase in proteolysis. Phytocystatins are plant inhibitors of cysteine proteinases that belong to the papain and legumain family. A cDNA encoding the protein inhibitor TrcC-8 was identified in the vegetative organs of triticale. In response to water-deficit, increases in the mRNA levels of TrcC-8 were observed in leaf and root tissues. Immunoblot analysis indicated that accumulation of the TrcC-8 protein occurred after 72h of water-deficit in the seedlings. Using recombinant protein, inhibitory activity of TrcC-8 against cysteine proteases from triticale and wheat tissues was analyzed. Under water-deficit conditions, there are increases in cysteine proteinase activities in both plant tissues. The cysteine proteinase activities were inhibited by addition of the recombinant TrcC-8 protein. These results suggest a potential role for the triticale phytocystatin in modulating cysteine proteinase activities during water-deficit conditions.