Differential Contribution of P5CS Isoforms to Stress Tolerance in Arabidopsis

Evaluation of the molecular and physiological response to dehydration of two accessions of the model plant Setaria viridis

Water deficits are responsible for countless agricultural losses. Among the affected crops, C4 plants are of special interest due to their high water and nitrogen use efficiency. Two accessions of Setaria viridis (Ast-1 and A10.1) with contrasting responses to water deficit were used in the current work to better understand the mechanisms behind drought tolerance in C4 species. Our results showed that although the A10.1 accession exhibited a reduced size and lower Rfd values in comparison to Ast-1, it had overall higher Fv/Fm and lower NPQ values in well-watered conditions. The water deficit induction was performed with PEG-8000 at the grain-filling stage using dehydration cycles. Analysis of physiological measurements showed the A10.1 accession as being more tolerant to multiple water deficit exposures. In addition, PCA identified a clear difference in the pattern of drought response of the accessions. Four drought marker genes previously described in the literature were chosen to evaluate the response at the molecular level: SvP5CS2, SvDHN1, SvNAC6, and SvWRKY1. Besides confirming that Ast-1 is a more sensitive accession, the expression analysis revealed that SvNAC1 might better monitor drought stress, while SvWRKY1 was able to differentiate the two accessions. Distinct evolutionary histories of each accession may be behind their differences in response to water deficits.

Overexpression of SCL30A from cassava (Manihot esculenta) negatively regulates salt tolerance in Arabidopsis

Soil salinity is a significant threat to sustainable agricultural production. Plants must adjust their developmental and physiological processes to deal with environmental salt conditions. We previously identified 18 serine-arginine-rich (SR) proteins from cassava (Manihot esculenta Crantz) that play pivotal roles in alternative splicing when encountering the external stress condition. However, functional characterisation of SR proteins is less reported in cassava, which is an important staple crop in the world. In the current study, we found that the expression of cassava spliceosomal component 35-like 30A (MeSCL30A) was significantly induced in response to drought and salt stress. The MeSCL30A overexpressing lines were also obtained in Arabidopsis thaliana L., which flowered earlier when compared with Col-0. Moreover, the MeSCL30A overexpressing lines were hypersensitive to salt and drought stress with lower germination and greening rate in comparison to Col-0. Importantly, soil-grown overexpression lines exhibited salt sensitivity through modulating the reactive oxygen species homeostasis and negatively regulating the gene expression that involved in ionic stress pathway. Therefore, these findings refined the SR protein-coding genes and provided novel insights for enhancing the resistance to environmental stress in plant.

The proline cycle as an eukaryotic redox valve

The amino acid proline has been known for many years to be a component of proteins as well as an osmolyte. Many recent studies have demonstrated that proline has other roles such as regulating redox balance and energy status. In animals and plants, the well-described proline cycle is concomitantly responsible for the preferential accumulation of proline and shuttling of redox equivalents from the cytosol to mitochondria. The impact of the proline cycle goes beyond regulating proline levels. In this review, we focus on recent evidence of how the proline cycle regulates redox status in relation to other redox shuttles. We discuss how the interconversion of proline and glutamate shuttles reducing power between cellular compartments. Spatial aspects of the proline cycle in the entire plant are considered in terms of proline transport between organs with different metabolic regimes (photosynthesis versus respiration). Furthermore, we highlight the importance of this shuttle in the regulation of energy and redox power in plants, through a particularly intricate coordination, notably between mitochondria and cytosol.

Physiological and Biochemical Traits of Two Major Arabidopsis Accessions, Col-0 and Ws, Under Salinity

Salinity affects plant growth and development as shown with the glycophyte model plant, Arabidopsis thaliana (Arabidopsis). Two Arabidopsis accessions, Wassilewskija (Ws) and Columbia (Col-0), are widely used to generate mutants available from various Arabidopsis seed resources. However, these two ecotypes are known to be salt-sensitive with different degrees of tolerance. In our study, 3-week-old Col-0 and Ws plants were treated with and without 150 mM NaCl for 48, 72, or 96 h, and several physiological and biochemical traits were characterized on shoots to identify any specific traits in their tolerance to salinity. Before salt treatment was carried out, a different phenotype was observed between Col-0 and Ws, whose main inflorescence stem became elongated in contrast to Col-0, which only displayed rosette leaves. Our results showed that Col-0 and Ws were both affected by salt stress with limited growth associated with a reduction in nutrient uptake, a degradation of photosynthetic pigments, an increase in protein degradation, as well as showing changes in carbohydrate metabolism and cell wall composition. These traits were often more pronounced in Col-0 and occurred usually earlier than in Ws. Tandem Mass Tags quantitative proteomics data correlated well with the physiological and biochemical results. The Col-0 response to salt stress was specifically characterized by a greater accumulation of osmoprotectants such as anthocyanin, galactinol, and raffinose; a lower reactive oxygen detoxification capacity; and a transient reduction in galacturonic acid content. Pectin degradation was associated with an overaccumulation of the wall-associated kinase 1, WAK1, which plays a role in cell wall integrity (CWI) upon salt stress exposure. Under control conditions, Ws produced more antioxidant enzymes than Col-0. Fewer specific changes occurred in Ws in response to salt stress apart from a higher number of different fascilin-like arabinogalactan proteins and a greater abundance of expansin-like proteins, which could participate in CWI. Altogether, these data indicate that Col-0 and Ws trigger similar mechanisms to cope with salt stress, and specific changes are more likely related to the developmental stage than to their respective genetic background.

Enzymology and Regulation of δ1-Pyrroline-5-Carboxylate Synthetase 2 From Rice

Under several stress conditions, such as excess salt and drought, many plants accumulate proline inside the cell, which is believed to help counteracting the adverse effects of low water potential. This increase mainly relies upon transcriptional induction of δ¹-pyrroline-5-carboxylate synthetase (P5CS), the enzyme that catalyzes the first two steps in proline biosynthesis from glutamate. P5CS mediates both the phosphorylation of glutamate and the reduction of γ-glutamylphosphate to glutamate-5-semialdehyde, which spontaneously cyclizes to δ¹-pyrroline-5-carboxylate (P5C). In most higher plants, two isoforms of P5CS have been found, one constitutively expressed to satisfy proline demand for protein synthesis, the other stress-induced. Despite the number of papers to investigate the regulation of P5CS at the transcriptional level, to date, the properties of the enzyme have been only poorly studied. As a consequence, the descriptions of post-translational regulatory mechanisms have largely been limited to feedback-inhibition by proline. Here, we report cloning and heterologous expression of P5CS2 from Oryza sativa. The protein has been fully characterized from a functional point of view, using an assay method that allows following the physiological reaction of the enzyme. Kinetic analyses show that the activity is subjected to a wide array of regulatory mechanisms, ranging from product inhibition to feedback inhibition by proline and other amino acids. These findings confirm long-hypothesized influences of both, the redox status of the cell and nitrogen availability, on proline biosynthesis.