Characterization of two Arabidopsis thaliana genes with roles in plant homeostasis

Philosophiae Doctor - PhDPlants are continuously exposed to varying conditions in their environment, to which they have to adapt by manipulating various cellular processes. Environmental (abiotic) and pathogen (biotic) stress are challenges against which plants have to defend themselves. Many plant responses to stress stimuli are a result of cellular processes that can be divided into three sequential steps; namely signal perception, signal transduction m1d execution of a response. Stress signal perception is, in most of these cases, facilitated by cell surface or intracellular receptors that act to recognize molecules presented to the cell. In several cases, hormones are synthesized in response to stress signals and in turn these hormones are perceived by cellular receptors that trigger signal transduction cascades. Propagation of signal transduction cascades is a complex process that results from activation of various signaling molecules within the cell. Second messengers like calcium (Ca2+) and guanosine 3', 5'-cyclic monophosphate (cGMP) play a vital role in mediating many signal transduction processes. The result of these signal transduction cascades is, in most instances, expression of genes that contribute to the plant's ability to cope with the challenges presented to it. Plant natriuretic peptides (PNPs) are novel plant hormones that regulate water and salt homeostasis via cGMP-dependent signaling pathways that involve deployment of Ca2+. The aim of this study is to partially characterize a PNP and a guanylyl cyclase, both from Arabidopsis thaliana. Guanylyl cyclases synthesize cGMP from the hydrolysis of guanosine 5' -triphosphate (GTP) in the cell. The study also aims to investigate the effect of drought and salinity on cGMP levels in plants, using sorbitol to mimic the osmolarity/dehydration effect of drought and NaCl as a source of salinity stress and thus link NaCl and sorbitol responses to both AtPNP-A and cGMP up-regulation

Nitric oxide (NO) regulates the expression of single-domain cystatins in glycine max (soybean)

Plant cystatins inhibit cysteine proteases and are important in regulating plant development and plant responses to biotic and abiotic stress. Furthermore, nitric oxide plays a signaling role in regulating plant responses to developmental processes, biotic and abiotic stress. With the aim of determining if nitric oxide is involved in the regulation of the expression of single-domain cystatins, we have identified single-domain cystatin genes in soybean (Glycine max cv. PAN626) on the basis of sequence homology to a nitric oxide-inducible cystatin (AtCYS1, At5g12140) from Arabidopsis thaliana. Analysis of the expression of the four cystatin genes revealed that transcript levels of these cystatins are altered by exogenously applied nitric oxide and a nitric oxide synthase inhibitor. Altered expression of these cystatins by nitric oxide and the nitric oxide synthase inhibitor implies that changes in cellular nitric oxide content, which have previously been shown to occur during development and/or biotic and abiotic stress, influence soybean physiological processes that are regulated by cysteine proteases. Recombinant protein expression of one of the cystatins (as a glutathione-S-transferase fusion protein) showed that it has inhibitory activity against the model cysteine protease papain but not the model serine protease trypsin and that it inhibits caspase-like activity in soybean nodule extracts. This serves as evidence that these four plant cystatins are functional cysteine protease inhibitors because of their high degree of primary sequence identity. It also indicates that the single-domain cystatins regulate caspase-like activity, which is known to participate in plant responses to biotic and abiotic stress. We thus conclude that nitric oxide and nitric oxide synthase-like activity regulate the expression of these cystatins, thus influencing soybean caspase-like activity. We also propose a role for this nitric oxide-mediated regulation of cystatin gene expression in the mediation of developmental processes and responses to abiotic stress in soybean.Web of Scienc

Drought and exogenous abscisic acid alter hydrogen peroxide accumulation and diferentially regulate the expression of two maize RD22-like genes

Increased biosynthesis of abscisic acid (ABA) occurs in plants in response to water defcit, which is mediated by changes in the levels of reactive oxygen species such as H2O2. Water defcit and ABA induce expression of some RD22-like proteins. This study aimed to evaluate the efect of water defcit and exogenous ABA (50µM ABA applied every 24hours for a total of 72hours) on H2O2 content in Zea mays (maize) and to characterise genes encoding two putative maize RD22-like proteins (designated ZmRD22A and ZmRD22B). The expression profles of the two putative maize RD22-like genes in response to water defcit and treatment with ABA were examined in leaves. In silico analyses showed that the maize RD22-like proteins share domain organisation with previously characterized RD22-like proteins. Both water defcit and exogenous ABA resulted in increased H2O2 content in leaves but the increase was more pronounced in response to water defcit than to exogenous ABA. Lignin content was not afected by exogenous ABA, whereas it was decreased by water defcit. Expression of both RD22- like genes was up-regulated by drought but the ZmRD22A gene was not infuenced by exogenous ABA, whereas ZmRD22B was highly responsive to exogenous ABA

Identification of a novel protein with guanylyl cyclase activity in Arabidopsis thaliana

Guanylyl cyclases (GCs) catalyze the formation of the second messenger guanosine 3 ,5 -cyclic monophos- phate (cGMP) from guanosine 5 -triphosphate (GTP). While many cGMP-mediated processes in plants have been reported, no plant molecule with GC activity has been identified. When the Arabidopsis thaliana genome is queried with GC sequences from cyanobacteria, lower and higher eukaryotes no unassigned proteins with sig- nificant similarity are found. However, a motif search of the A. thaliana genome based on conserved and func- tionally assigned amino acids in the catalytic center of annotated GCs returns one candidate that also contains the adjacent glycine-rich domain typical for GCs

Genetic variation in responses to salt stress in Tunisian populations of Medicago ciliaris

Soil salinity is one of the most serious environmental factors affecting crop productivity around the world. We used a morpho-physiological approach to investigate the salt responses of four Tunisian natural populations of Medicago ciliaris. Forty-six lines of M. ciliaris were grown under a control treatment and 100 mM NaCl. We measured 11 quantitative traits of shoot and root growth during harvest. An analysis of variance showed that the variations in salt response can be explained by the effects of the population, line, treatment, and interactions between the population and treatment and the line and treatment. Most of the measured traits showed significant differences between the studied populations under the control treatment and salt stress

Evaluation of the morpho-physiological, biochemical and molecular responses of contrasting medicago truncatula lines under water deficit stress

Medicago truncatula is a forage crop of choice for farmers, and it is a model species for molecular research. The growth and development and subsequent yields are limited by water availability mainly in arid and semi-arid regions. Our study aims to evaluate the morpho-physiological, biochemical and molecular responses to water deficit stress in four lines (TN6.18, JA17, TN1.11 and A10) of M. truncatula. The results showed that the treatment factor explained the majority of the variation for the measured traits. It appeared that the line A10 was the most sensitive and therefore adversely affected by water deficit stress, which reduced its growth and yield parameters, whereas the tolerant line TN6.18 exhibited the highest root biomass production, a significantly higher increase in its total protein and soluble sugar contents, and lower levels of lipid peroxidation with greater cell membrane integrity. The expression analysis of the DREB1B gene using RT-qPCR revealed a tissue-differential expression in the four lines under osmotic stress, with a higher induction rate in roots of TN6.18 and JA17 than in A10 roots, suggesting a key role for DREB1B in water deficit tolerance in M. truncatula

Morpho-physiological, biochemical, and genetic responses to salinity in medicago truncatula

We used an integrated morpho-physiological, biochemical, and genetic approach to investigate the salt responses of four lines (TN1.11, TN6.18, JA17, and A10) of Medicago truncatula. Results showed that TN1.11 exhibited a high tolerance to salinity, compared with the other lines, recording a salinity induced an increase in soluble sugars and soluble proteins, a slight decrease in malondialdehyde (MDA) accumulation, and less reduction in plant biomass. TN6.18 was the most susceptible to salinity as it showed less plant weight, had elevated levels of MDA, and lower levels of soluble sugars and soluble proteins under salt stress. As transcription factors of the APETALA2/ethylene responsive factor (AP2/ERF) family play important roles in plant growth, development, and responses to biotic and abiotic stresses, we performed a functional characterization of MtERF1 gene. Real-time PCR analysis revealed that MtERF1 is mainly expressed in roots and is inducible by NaCl and low temperature

Antioxidant responses are associated with differences in drought tolerance between maize and sorghum

Drought is a major cause of decreased yield in crops worldwide. Sorghum (Sorghum bicolor) and maize (Zea mays) are two of the key crops in Africa serving as human food as well as livestock feed. For improved crop production, selection for drought resilient genotypes is imperative and the biological basis for drought tolerance ought to be fully understood to achieve such selection. Sorghum can tolerate drought better than maize and it is a key model for studying the physiological and biochemical mechanisms conferring drought tolerance. In this study, comparative analyses in terms of changes in growth, chlorophyll content, ROS content, lipid peroxidation level and the activity of antioxidant enzymes were investigated. Exposure to drought triggered ROS generation in both plant species. However, sorghum showed less cell damage under water deficit compared to maize. Furthermore, differences in antioxidant enzyme activity between maize and sorghum were identified. Our findings reveal differences in and association between the physiological and biochemical responses of maize and sorghum to drought, which may be relevant for breeding drought tolerant crops

Assessment of genetic diversity in Tunisian populations of Medicago polymorpha based on SSR markers

Medicago polymorpha L. is a herbaceous legume that can be a useful pasture crop, especially in Mediterranean climates. This study aimed to analyze the genetic variation in five populations of M. polymorpha collected from different ecogeographic regions in Tunisia using eight SSR markers. The transferability of 112 SSR markers distributed on the eight chromosomes of M. truncatula Gaertn. showed that 50 SSR markers could be amplified in M. polymorpha. Among these 50 SSR markers, eight (8) markers were polymorphous. A high level of polymorphism (126 polymorphic alleles with an average of 5.3 alleles per locus) and a moderate level of genetic diversity were found in all the studied populations, with observed and expected heterozygosities averaging between 0 and 0.69, respectively. Results from analysis of molecular variance (AMOVA) revealed that the most variation was found within populations (76%). Moderate levels of population differentiation (FST = 0.12 to 0.19) accompanied by a high rate of gene flow between populations (Nm = 1.08 to 1.83) were recorded. This molecular differentiation (FST) was not dependent on geographical distances (r = 0.395, p = 0.524), suggesting that studied populations are not geographically isolated. Our results showed that studied populations were clustered into three groups. A first group is formed by the populations of El Kef (TNP7) and Bulla Regia (TNP9), a second group of Enfidha (TNP1) and a third group of Soliman (TNP8) and Mateur (TNP11). Results obtained in our study could be helpful for breeders considering introduction of some lines of this species into M. polymorpha breeding programs

Common bean as a potential crop for future food security: an overview of past, current and future contributions in genomics, transcriptomics, transgenics and proteomics

Common bean is an important legume crop having high quality protein, micronutrients, vitamins and antioxidants, which makes it a “grain of hope” for poor communities. Hence, a good number of breeding activities have been performed on the improvement of various key traits for years. However, recent advancements in molecular markers, sequencing technologies and the completion of the common bean genome sequence have opened numerous opportunities for fine mapping and gene characterization. The availability of these tools together with investigations of quantitative trait loci (QTL) and candidate genes for key traits such as morpho-agronomic, iron and zinc contents, cooking and quality traits, antioxidant activity, biotic and abiotic stresses pave the way to the development of new strategies for common bean genetic improvement. As a food source, it can contribute to the reduction of food scarcity worldwide in the coming years. Therefore, it is very important to take synergic efforts to integrate common bean genetic and genomic resources in breeding activities to ensure food security and contribute significantly to improved livelihoods in developing countries. Moreover, Kompetitive allele specific PCR (KASP) and CRISPR-Cas9 should be used to develop climate resilience common bean varieties. Here, we provide an overview of the evolution of common bean research by highlighting the past and recent advances in genomics, transgenics, transcriptomics and proteomics and also critically discuss the future prospects for further genetic improvement and better expansion of this crop