No abstract

Salt tolerance is an important trait that is required to overcome salinity-induced reduction in plant productivity. We have reported previously the isolation of a pea DNA helicase 45 (PDH45) that exhibits striking homology with the eukaryotic translation initiation factor eIF-4A. Here, we report that PDH45 mRNA is induced in pea seedlings in response to high salt, and its overexpression driven by a constitutive cauliflower mosaic virus-35 S promoter in tobacco plants confers salinity tolerance, thus suggesting a previously undescribed pathway for manipulating stress tolerance in crop plants. The T0 transgenic plants showed high levels of PDH45 protein in normal and stress conditions, as compared with WT plants. The T0 transgenics also showed tolerance to high salinity as tested by a leaf disk senescence assay. The T1 transgenics were able to grow to maturity and set normal viable seeds under continuous salinity stress without any reduction in plant yield in terms of seed weight. Measurement of Na ؉ ions in different parts of the plant showed higher accumulation in the old leaves and negligible accumulation in seeds of T1 transgenic lines as compared with the WT plants. The possible mechanism of salinity tolerance is discussed. Overexpression of PDH45 provides a possible example of the exploitation of DNA͞RNA unwinding pathways for engineering salinity tolerance without affecting yield in crop plants.DEAD box protein ͉ eIF-4A ͉ salinity stress S oil salinity is an increasing threat for agriculture and is a major factor in reducing plant productivity; therefore, it is necessary to obtain salinity-tolerant varieties. A typical characteristic of soil salinity is the induction of multiple stress-inducible genes (1). Some of the genes encoding osmolytes (2), ion channels (3), or enzymes (4, 5) are able to confer salinity-tolerant phenotypes when transferred to sensitive plants. Because salinity stress affects the cellular gene-expression machinery, it is evident that molecules involved in nucleic acid processing, including helicases, are likely to be affected as well. DNA helicases unwind duplex DNA and are involved in replication, repair, recombination, and transcription, whereas RNA helicases unfold the secondary structures in RNA and are involved in transcription, ribosome biogenesis, and translation initiation (6, 7). Most helicases are members of the DEAD-box protein superfamily, and the eukaryotic translation initiation factor (eIF-4A) is a prototypic member of this family (7,8). It is an essential component of the cap-binding complex that facilitates ribosome assembly on mRNA by unwinding the secondary structures in the 5Ј untranslated region (9).The involvement of RNA helicases in response to stress has been reported previously. The cyanobacterial, CrhC (10), Clostridium perfringes RNA helicase (11), and fission yeast DEAD-box protein, Ded1 (12), respond to cold, oxidative, and cellular stress, respectively. There is also evidence for the involvement of the mammalian RNA helicase, RHII͞Gu, in RNA polymerase II...

MicroRNAs (miRNAs) are a class of small non-coding RNAs that have recently emerged as important regulators of gene expression, mainly through cleavage and/or translation inhibition of the target mRNAs during or after transcription. miRNAs play important roles by regulating a multitude of biological processes in plants which include maintenance of genome integrity, development, metabolism, and adaptive responses toward environmental stresses. The increasing population of the world and their food demands requires focused efforts for the improvement of crop plants to ensure sustainable food production. Manipulation of mRNA transcript abundance via miRNA control provides a unique strategy for modulating differential plant gene expression and miRNAs are thus emerging as the next generation targets for genetic engineering for improvement of the agronomic properties of crops. However, a deeper understanding of its potential and the mechanisms involved will facilitate the design of suitable strategies to obtain the desirable traits with minimum trade-offs in the modified crops. In this regard, this review highlights the diverse roles of conserved and newly identified miRNAs in various food and industrial crops and recent advances made in the uses of miRNAs to improve plants of agronomically importance so as to significantly enhance crop yields and increase tolerance to various environmental stress agents of biotic-or abiotic origin.

Serotonin (Ser) and melatonin (Mel) serve as master regulators of plant growth and development by influencing diverse cellular processes. The enzymes namely, tryptophan decarboxylase (TDC) and tryptamine 5-hydroxylase (T5H) catalyse the formation of Ser from tryptophan. Subsequently, serotonin N-acetyl transferase (SNAT) and acetyl-serotonin methyltransferase (ASMT) form Mel from Ser. Plant genomes harbour multiple genes for each of these four enzymes, all of which have not been identified. Therefore, to delineate information regarding these four gene families, we carried out a genome-wide analysis of the genes involved in Ser and Mel biosynthesis in Arabidopsis, tomato, rice and sorghum. Phylogenetic analysis unravelled distinct evolutionary relationships among these genes from different plants. Interestingly, no gene family except ASMTs showed monocot- or dicot-specific clustering of respective proteins. Further, we observed tissue-specific, developmental and stress/hormone-mediated variations in the expression of the four gene families. The light/dark cycle also affected their expression in agreement with our quantitative reverse transcriptase-PCR (qRT-PCR) analysis. Importantly, we found that miRNAs (miR6249a and miR-1846e) regulated the expression of Ser and Mel biosynthesis under light and stress by influencing the expression of OsTDC5 and OsASMT18, respectively. Thus, this study may provide opportunities for functional characterization of suitable target genes of the Ser and Mel pathway to decipher their exact roles in plant physiology.

Most of the physiological processes are controlled by the small RNAs in several organisms including plants. A huge database exists on one type of small RNA, i.e., microRNAs (miRs) identified from diverse species. However, the processes of data-mining of miRs in most of the species are still incomplete. Rice feeds the hungry trillions and hence understanding its developmental processes as well as its stress biology, which might be largely controlled by the small RNA pathways, is certainly a worthwhile task. Here, we report the cloning and identification of approximately 40 new putative miRs from local basmati rice variety in accordance to the annotation suggested by Meyers et al. (Plant Cell 20:3186-3190, 2008). About 23 sequences were derived from rice exposed to salt stress while 18 were derived from rice infected with tungro virus. A few of these putative miRs were common to both. Our data showed that at least two of these miRs were up-regulated in response to both abiotic and biotic stresses. The miR target predictions indicate that most of the putative miRs target specific metabolic processes. The up-regulation of similar miRs in response to two entirely different types of stresses suggests a converging functional role of miRs in managing various stresses. Our findings suggest that more rice miRs need to be identified and a thorough understanding of the function of such miRs will help unravel the mysteries of rice stress biology.