Involvement of mitogen activated protein kinase kinase 6 in UV induced transcripts accumulation of genes in phytoalexin biosynthesis in rice

Rice Mitogen-Activated Protein Kinase regulates serotonin accumulation and interacts with cell cycle regulators under prolonged UV-B exposure

Stress conditions such as UV-B exposure activates MAPKs in Arabidopsis and rice. UV-B radiation is hazardous to plant as it causes photosystem disruption, DNA damage and ROS generation. Here we report its effect on biological pathways by studying the global changes in transcript profile in rice seedling exposed to UV-B radiation for 1 h and 16 h. Short UV-B exposure (1 h) led to moderate changes, while a drastic change in transcript landscape was observed after long term UV-B exposure (16 h) in rice seedlings. Prolonged UV-B exposure negatively impacts the expression of cell cycle regulating genes and several other metabolic pathways in developing seedlings. MAP kinase signaling cascade gets activated upon UV-B exposure similar to reports in Arabidopsis indicating conservation of its function in both dicot and monocot. Expression analysis in inducible overexpression transgenic lines of MPK3 and MPK6 shows higher transcript abundance of phytoalexin biosynthesis gene like Oryzalexin D synthase and Momilactone A synthase, along with serotonin biosynthesis genes. An accumulation of serotonin was observed upon UV-B exposure and its abundance positively correlates with the MPK3 and MPK6 transcript level in the respective over-expression lines. Interestingly, multiple cell cycle inhibitor proteins including WEE1 and SMR1 interact with MPK3 and MPK6 thus, implying a major role of this pathway in cell cycle regulation under stress condition. Overall overexpression of MPK3 and MPK6 found to be detrimental for rice as overexpression lines shows higher cell death and compromised tolerance to UV-B.

Recent advances in physiological and molecular mechanisms of heavy metal accumulation in plants

Among abiotic stress, the toxicity of metals impacts negatively on plants' growth and productivity. This toxicity promotes various perturbations in plants at different levels. To withstand stress, plants involve efficient mechanisms through the implication of various signaling pathways. These pathways enhance the expression of many target genes among them gene coding for metal transporters. Various metal transporters which are localized at the plasma membrane and/or at the tonoplast are crucial in metal stress response. Furthermore, metal detoxification is provided by metal-binding proteins like phytochelatins and metallothioneins. The understanding of the molecular basis of metal toxicities signaling pathways and tolerance mechanisms is crucial for genetic engineering to produce transgenic plants that enhance phytoremediation. This review presents an overview of the recent advances in our understanding of metal stress response. Firstly, we described the effect of metal stress on plants. Then, we highlight the mechanisms involved in metal detoxification and the importance of the regulation in the response to heavy metal stress. Finally, we mentioned the importance of genetic engineering for enhancing the phytoremediation technique. In the end, the response to heavy metal stress is complex and implicates various components. Thus, further studies are needed to better understand the mechanisms involved in response to this abiotic stress.

Genome-wide analysis of mitogen-activated protein (MAP) kinase gene family expression in response to biotic and abiotic stresses in sugarcane

To systematically analyze mitogen-activated protein (MAP) kinase gene families and their expression profiles in sugarcane (Saccharum spp. hybrids; Sh) under diverse biotic and abiotic stresses, we identified 15 ShMAPKs, 6 ShMAPKKs and 16 ShMAPKKKs genes in the sugarcane cultivar R570 genome. These were also confirmed in one S. spontaneum genome and two transcriptome datasets of sugarcane trigged by Acidovorax avenae subsp. avenae (Aaa) and Xanthomonas albilineans (Xa) infections. Phylogenetic analysis revealed that four subgroups were present in each ShMAPK and ShMAPKK family and three sub-families (RAF, MEKK and ZIK) presented in the ShMAPKKK family. Conserved protein motif and gene structure analyses supported the evolutionary relationships of the three families inferred from the phylogenetic analysis. All of the ShMAPK, ShMAPKK and ShMAPKKK genes identified in Saccharum spp. R570 were distributed on chromosomes 1-7 and 9-10. RNA-seq and qRT-PCR analyses indicated that ShMAPK07 and ShMAPKKK02 were defense-responsive genes in sugarcane challenged by both Aaa and Xa stimuli, while some genes were upregulated specifically by Aaa and Xa infection. Additionally, ShMAPK05 acted as a negative regulator under drought and salinity stress, but served as a positive regulator under salicylic acid (SA) treatment. ShMAPK07 plays a positive role under drought stress, but a negative role under SA treatment. ShMAPKKK01 was negatively modulated by both salinity stress and SA treatment, whereas ShMAPKKK06 was positively regulated by both of the two stress stimuli. Our results suggest that members of MAPK cascade gene families regulate adverse stress responses through multiple signal transduction pathways in sugarcane.

Development of efficient protocol for rice transformation overexpressing MAP kinase and their effect on root phenotypic traits

Exhaustive studies on mitogen-activated protein kinase (MAPK) have reported the importance in regulating a variety of responses during plant growth and development. In particular, the potential MAPK genes, MPK3 and MPK6, seem to regulate a plethora of responses, conferring tolerance to varied abiotic, biotic, and developmental stimuli. This makes both MPK3 and MPK6 potential targets for further studies. It would be an important concern to overexpress and knock out these pivotal proteins and then, in turn, to monitor the plant response which is expected to correlate action of a gene to a trait in cellular and organismal contexts. However, overexpression of MAPK genes has remained a puzzle in plants. In the present study, we report the generation of stable transgenic lines overexpressing OsMPK3 in indica and japonica cultivars and OsMPK6 in japonica cultivar under the control of an inducible promoter. We also establish the crucial steps and troubleshooting for each of the indicated rice transformation medium components. Later, we study the potential role of these MAPKs in high-throughput analysis of root system architectural (RSA) traits. It was observed that OsMPK6 overexpression lines had a more robust and spread out root architectural system while OsMPK3 overexpression lines had a typical bushy phenotype.

Possible role of plant MAP kinases in the biogenesis and transcription regulation of rice microRNA pathway factors

Signalling pathways play vital roles as determinants of almost all the molecular processes inside a eukaryotic cell. They are more often considered to be the link between extracellular and intracellular environmental cues. Gene silencing pathways have emerged to be involved in regulation of stress responses and developmental processes. However, very little is known about the crosstalk between signalling and silencing pathways and their influence on each other. The present work describes the effects of general protein kinase inhibitors and specific mitogen activated protein kinase (MAPK) pathway inhibitors on the components of microRNA pathway in rice. The kinase inhibitors significantly reduced the activities of miRNA biogenesis complex and changed the transcript expression of miRNA pathway factors. This study suggests a possible regulation of microRNA machinery by plant kinases and MAP kinases in particular.

Rice Improvement Through Genome-Based Functional Analysis and Molecular Breeding in India

Rice is one of the main pillars of food security in India. Its improvement for higher yield in sustainable agriculture system is also vital to provide energy and nutritional needs of growing world population, expected to reach more than 9 billion by 2050. The high quality genome sequence of rice has provided a rich resource to mine information about diversity of genes and alleles which can contribute to improvement of useful agronomic traits. Defining the function of each gene and regulatory element of rice remains a challenge for the rice community in the coming years. Subsequent to participation in IRGSP, India has continued to contribute in the areas of diversity analysis, transcriptomics, functional genomics, marker development, QTL mapping and molecular breeding, through national and multi-national research programs. These efforts have helped generate resources for rice improvement, some of which have already been deployed to mitigate loss due to environmental stress and pathogens. With renewed efforts, Indian researchers are making new strides, along with the international scientific community, in both basic research and realization of its translational impact.

Functional Involvement of a Mitogen Activated Protein Kinase Module, OsMKK3-OsMPK7-OsWRK30 in Mediating Resistance against Xanthomonas oryzae in Rice

Mitogen-activated protein kinases (MAPKs) are highly conserved signaling modules in eukaryotes, transmitting signals from upstream receptor to downstream target by phosphorelay mechanism. Here we report involvement of a poorly characterized group C MAPK of rice namely, OsMPK7 along with its upstream MAPK kinase, OsMKK3 and downstream target, OsWRKY30 during Xanthomonas oryzae infection, a causal agent of leaf blight disease in rice. X. oryzae infection resulted in induction of OsMPK7 and OsMKK3. OsMKK3 was found to physically interact and phosphorylate OsMPK7. Overexpression of OsMPK7 and OsMKK3, individually and in combinations resulted in inhibition of disease symptoms caused by X. oryzae, however silencing of OsMPK7 resulted in disease susceptibility. Furthermore, OsWRKY30 was identified as downstream target of OsMPK7 through protein-protein interaction techniques and was found to be a positive regulator of defence response against X. oryzae pathogen. The overexpression of OsMKK3-OsMPK7 upregulated genes involved in pathogenesis, cell wall structure maintenance and cell metabolism indicating possible mechanism of disease resistance. These leaves also showed restricted movement of the pathogen from the point of infection to uninfected area. Taken together, this work suggests a positive involvement of OsMKK3-OsMPK7-OsWRKY30 module in imparting disease resistance against X. oryzae infection in rice.

ROS mediated MAPK signaling in abiotic and biotic stress- striking similarities and differences

Plants encounter a number of environmental stresses throughout their life cycles, most of which activate mitogen activated protein kinase (MAPK) pathway. The MAPKs show crosstalks at several points but the activation and the final response is known to be specific for particular stimuli that in-turn activates specific set of downstream targets. Interestingly, reactive oxygen species (ROS) is an important and common messenger produced in various environmental stresses and is known to activate many of the MAPKs. ROS activates a similar MAPK in different environmental stimuli, showing different downstream targets with different and specific responses. In animals and yeast, the mechanism behind the specific activation of MAPK by different concentration and species of ROS is elaborated, but in plants this aspect is still unclear. This review mainly focuses on the aspect of specificity of ROS mediated MAPK activation. Attempts have been made to review the involvement of ROS in abiotic stress mediated MAPK signaling and how it differentiates with that of biotic stress.

Genome-wide transcriptome modulation in rice transgenic lines expressing engineered mitogen activated protein kinase kinase 6

Mitogen activated protein kinase kinase (MAPKK) is the central module of MAPK cascade and also point of signal integration and divergence. To investigate the regulatory role of OsMKK6, the regulon of genes controlled by OsMKK6 was constructed by microarray analysis between constitutively activated overexpressing transgenic lines and the wild type rice. Regulated genes were identified in overexpressed constitutively activated OsMKK6 and they were further subdivided on the basis of functional categories, viz. transcription, metabolism, signaling, defense and unknown function. These findings suggest the possible physiological role of OsMKK6 in modulating gene expression and signaling pathways during different stresses.