Unraveling salt stress signaling in plants

Salt stress is a major environmental factor limiting plant growth and productivity. A better understanding of the mechanisms mediating salt resistance will help researchers design ways to improve crop performance under adverse environmental conditions. Salt stress can lead to ionic stress, osmotic stress and secondary stresses, particularly oxidative stress, in plants. Therefore,to adapt to salt stress, plants rely on signals and pathways that re-establish cellular ionic, osmotic, and reactive oxygen species(ROS) homeostasis. Over the past two decades, genetic and biochemical analyses have revealed several core stress signaling pathways that participate in salt resistance. The Salt Overly Sensitive signaling pathway plays a key role in maintaining ionic homeostasis,via extruding sodium ions into the apoplast. Mitogenactivated protein kinase cascades mediate ionic, osmotic,and ROS homeostasis. SnR K2(sucrose nonfermenting1-related protein kinase 2) proteins are involved in maintaining osmotic homeostasis. In this review, we discuss recent progress in identifying the components and pathways involved in the plant's response to salt stress and their regulatory mechanisms. We also review progress in identifying sensors involved in salt-induced stress signaling in plants.     

Developmental control of stress stimulons in Streptomyces coelicolor revealed by statistical analyses of global gene expression patterns

Stress-induced regulatory networks coordinated with a procaryotic developmental program were revealed by two-dimensional gel analyses of global gene expression. Four developmental stages were identified by their distinctive protein synthesis patterns using principal component analysis. Statistical analyses focused on five stress stimulons (induced by heat, cold, salt, ethanol, or antibiotic shock) and their synthesis during development. Unlike other bacteria, for which various stresses induce expression of similar sets of protein spots, in Streptomyces coelicolor heat, salt, and ethanol stimulons were composed of independent sets of proteins. This suggested independent control by different physiological stress signals and their corresponding regulatory systems. These stress proteins were also under developmental control. Cluster analysis of stress protein synthesis profiles identified 10 different developmental patterns or "synexpression groups." Proteins induced by cold, heat, or salt shock were enriched in three developmental synexpression groups. In addition, certain proteins belonging to the heat and salt shock stimulons were coregulated during development. Thus, stress regulatory systems controlling these stimulons were implicated as integral parts of the developmental program. This correlation suggested that thermal shock and salt shock stress response regulatory systems either allow the cell to adapt to stresses associated with development or directly control the developmental program.     

The combined effect of salt stress and heat shock on proteome profiling in Suaeda salsa

Under natural conditions or in the field, plants are often subjected to a combination of different stresses such as salt stress and heat shock. Although salt stress and heat shock have been extensively studied, little is known about how their combination affects plants. We used proteomics, coupled with physiological measurements, to investigate the effect of salt stress, heat shock, and their combination on Suaeda salsa plants. A combination of salt stress and heat shock resulted in suppression of CO₂ assimilation and the photosystem II efficiency. Approximately 440 protein spots changed their expression levels upon salt stress, heat shock and their combination, and 57 proteins were identified by MS. These proteins were classified into several categories including disease/defense, photosynthesis, energy production, material transport, and signal transduction. Some proteins induced during salt stress, e.g. choline monooxygenase, chloroplastic ATP synthase subunit beta, and V-type proton ATPase catalytic subunit A, and some proteins induced during heat shock, e.g. heat shock 70 kDa protein, probable ion channel DMI1, and two component sensor histidine kinase, were either unchanged or suppressed during a combination of salt stress and heat shock. In contrast, the expression of some proteins, including nucleoside diphosphate kinase 1, chlorophyll a/b binding protein, and ABC transporter I family member 1, was specifically induced during a combination of salt stress and heat shock. The potential roles of the stress-responsive proteins are discussed.     

Wounding increases salt tolerance in tomato plants: evidence on the participation of calmodulin-like activities in cross-tolerance signalling

Cross-tolerance is the phenomenon by which a plant resistance to a stress results in resistance to another form of stress. It has previously been shown that salt stress causes the accumulation of proteinase inhibitors and the activation of other wound-related genes in tomato plants (Solanum lycopersicum). However, very little is known about how different stresses interact with one another, and which are the signalling components that interrelate the responses triggered by different stress types. In the present work, it is shown that mechanical wounding increases salt-stress tolerance in tomato plants through a mechanism that involves the signalling peptide systemin and the synthesis of JA. Data are also provided indicating that calmodulin-like activities are necessary for the downstream signalling events that lead to cross-tolerance between wounding and salt stress. Finally, evidence was gathered supporting the hypothesis that LeCDPK1, a Ca2+ -dependent protein kinase from tomato previously described in our laboratory, could participate in this cross-tolerance mechanism interrelating the signalling responses to wounding and salt stress.