A glutathione-independent DJ-1/PfpI domain-containing tomato glyoxalaseIII2, SlGLYIII2, confers enhanced tolerance under salt and osmotic stresses.

In plants, glyoxalase enzymes are activated under stress conditions to mitigate the toxic effects of hyperaccumulated methylglyoxal (MG), a highly reactive carbonyl compound. Until recently, a glutathione-dependent bi-enzymatic pathway involving glyoxalase I (GLYI) and glyoxalase II (GLYII) was considered the primary MG-detoxification system. Recently, a new glutathione-independent glyoxalase III (GLYIII) mediated direct route was also reported in plants. However, the physiological significance of this new pathway remains to be elucidated across plant species. This study identified the full complement of 22 glyoxalases in tomato. Based on their strong induction under multiple abiotic stresses, SlGLYI4, SlGLYII2 and SlGLYIII2 were selected candidates for further functional characterisation. Stress-inducible overexpression of both glutathione-dependent (SlGLYI4 + SlGLYII2) and independent (SlGLYIII2) pathways led to enhanced tolerance in both sets of transgenic plants under abiotic stresses. However, SlGLYIII2 overexpression (OE) plants outperformed the SlGLYI4 + SlGLYII2 OE counterparts for their stress tolerance under abiotic stresses. Further, knockdown of SlGLYIII2 resulted in plants with exacerbated stress responses than those silenced for both SlGLYI4 and SlGLYII2. The superior performance of SlGLYIII2 OE tomato plants for better growth and yield under salt and osmotic treatments could be attributed to better GSH/GSSG ratio, lower reactive oxygen species levels, and enhanced antioxidant potential, indicating a prominent role of GLYIII MG-detoxification pathway in abiotic stress mitigation in this species.

Genome-wide analysis of genes encoding MBD domain-containing proteins from tomato suggest their role in fruit development and abiotic stress responses.

In tomato, DNA methylation has an inhibitory effect on fruit ripening. The inhibition of DNA methyltransferase by 5-azacytidine results in premature fruit ripening. Methyl CpG binding domain (MBD) proteins are the readers of DNA methylation marks and help in the recruitment of chromatin-modifying enzymes which affect gene expression. Therefore, we investigate their contribution during fruit development. In this study, we identified and analyzed 18 putative genes of Solanum lycopersicum and Solanum pimpinellifolium encoding MBD proteins. We also identified tomato MBD syntelogs in Capsicum annum and Solanum tuberosum. Sixty-three MBD genes identified from four different species of solanaceae were classified into three groups. An analysis of the conserved domains in these proteins identified additional domains along with MBD motif. The transcript profiling of tomato MBDs in wild-type and two non-ripening mutants, rin and Nr, indicated constructive information regarding their involvement during fruit development. When we performed a stage-specific expression analysis during fruit ripening, a gradual decrease in transcript accumulation in the wild-type fruit was detected. However, a very low expression was observed in the ripening mutants. Furthermore, many ethylene-responsive cis-elements were found in SlMBD gene promoters, and some of them were induced in the presence of exogenous ethylene. Further, we detected the possible role of these MBDs in abiotic stresses. We found that few genes were differentially expressed under various abiotic stress conditions. Our results provide an evidence of the involvement of the tomato MBDs in fruit ripening and abiotic stress responses, which would be helpful in further studies on these genes in tomato fruit ripening.

An Overview of Signaling Regulons During Cold Stress Tolerance in Plants.

Plants, being sessile organisms, constantly withstand environmental fluctuations, including low-temperature, also referred as cold stress. Whereas cold poses serious challenges at both physiological and developmental levels to plants growing in tropical or sub-tropical regions, plants from temperate climatic regions can withstand chilling or freezing temperatures. Several cold inducible genes have already been isolated and used in transgenic approach to generate cold tolerant plants. The conventional breeding methods and marker assisted selection have helped in developing plant with improved cold tolerance, however, the development of freezing tolerant plants through cold acclimation remains an unaccomplished task. Therefore, it is essential to have a clear understanding of how low temperature sensing strategies and corresponding signal transduction act during cold acclimation process. Herein, we synthesize the available information on the molecular mechanisms underlying cold sensing and signaling with an aim that the summarized literature will help develop efficient strategies to obtain cold tolerant plants.

Fruit preferential activity of the tomato RIP1 gene promoter in transgenic tomato and Arabidopsis.

Isolation and functional characterization of tissue- and stage-specific gene promoters is beneficial for genetic improvement of economically important crops. Here, we have characterized a putative promoter of a ripening-induced gene RIP1 (Ripening induced protein 1) in tomato. Quantification of the transcript level of RIP1 showed that its expression is fruit preferential, with maximum accumulation in red ripe fruits. To test the promoter activity, we made a reporter construct by cloning 1450 bp putative RIP1 promoter driving the GUS (ß-glucuronidase) gene expression and generated stable transgenic lines in tomato and Arabidopsis. Histochemical and fluorometric assays validated the fruit-specific expression of RIP1 as the highest GUS activity was found in red ripe tomatoes. Similarly, we detected high levels of GUS activity in the siliques of Arabidopsis. On the contrary, weak GUS activity was found in the flower buds in both tomato and Arabidopsis. To characterize the specific regions of the RIP1 promoter that might be essential for its maximum activity and specificity in fruits, we made stable transgenic lines of tomato and Arabidopsis with 5'-deletion constructs. Characterization of these transgenic plants showed that the full length promoter is essential for its function. Overall, we report the identification and characterization of a ripening-induced promoter of tomato, which would be useful for the controlled manipulation of the ripening-related agronomic traits in genetic manipulation studies in future.

Evolutionary Profiling of Group II Pyridoxal-Phosphate-Dependent Decarboxylases Suggests Expansion and Functional Diversification of Histidine Decarboxylases in Tomato.

Pyridoxal phosphate (PLP)-dependent enzymes are one of the most important enzymes involved in plant N metabolism. Here, we explored the evolution of group II PLP-dependent decarboxylases (PLP_deC), including aromatic L-amino acid decarboxylase, glutamate decarboxylase, and histidine decarboxylase in the plant lineage. Gene identification analysis revealed a higher number of genes encoding PLP_deC in higher plants than in lower plants. Expression profiling of PLP_deC orthologs and syntelogs in (L.) Heynh., pepper ( L.), and tomato ( L.) pointed toward conserved as well as distinct roles in developmental processes such as fruit maturation and ripening and abiotic stress responses. We further characterized a putative promoter of tomato ripening-associated gene () operating in a complex regulatory circuit. Our analysis provides a firm basis for further in-depth exploration of the PLP_deC gene family, particularly in the economically important Solanaceae family.