OsSGL, a novel pleiotropic stress-related gene enhances grain length and yield in rice.

Abiotic stress seriously affects the yield of rice (Oryza sativa L.). Grain yield in rice is multiplicatively determined by the number of panicles, number of grains per panicle, and grain weight. Here, we describe the molecular and functional characterization of STRESS_tolerance and GRAIN_LENGTH (OsSGL), a rice gene strongly up-regulated by a wide spectrum of abiotic stresses. OsSGL encodes a putative member of the DUF1645 protein family of unknown function. Overexpression of OsSGL significantly altered certain development processes greatly and positively affecting an array of traits in transgenic rice plants, including increased grain length, grain weight and grain number per panicle, resulting in a significant increase in yield. Microscopical analysis showed that the enhanced OsSGL expression promoted cell division and grain filling. Microarray and quantitative real-time PCR (qRT-PCR) analyses revealed that a large number of genes involved in stress-response, cell cycle and cytokinin signaling processes were induced or suppressed in OsSGL-overexpressing plants. Together, our results suggest that OsSGL may regulate stress-tolerance and cell growth by acting via a cytokinin signaling pathway. This study not only contributes to our understanding of the underlying mechanism regulating rice stress-tolerance and grain length, but also provides a strategy for tailor-made crop yield improvement.

Plant abiotic stress-related RCI2/PMP3s: multigenes for multiple roles.

MAIN CONCLUSION: RCI2 / PMP3 s participate in abiotic stress responses and impact the expression of other genes. Their multifunctionality is determined by differential expression and by distinct activities of their structurally different proteins. In plants, RCI2/PMP3 genes, which encode small membrane proteins of the PMP3 family, are closely associated with abiotic stress responses. Their involvement in mediating stress tolerance is supported by genetic evidence and overexpression studies. RCI2/PMP3s occur as multigenes in plant genomes and their encoded proteins belong to distinct and conserved structural groups. In addition, different isoforms appear to be targeted to the plasma membrane or to distinct endomembrane compartments in cells. Several studies have revealed that RCI2/PMP3 proteins participate in cell ion homeostasis, and in regulation of membrane stability and polarization. They also appear to potentiate plant transcriptional responses to abiotic stresses. However, their mechanisms of action remain unknown. This paper reviews the current knowledge of the multiple roles of plant RCI2/PMP3 genes resulting from their differential expression under normal and stress conditions. The structural diversity of RCI2/PMP3 proteins is analyzed and evidence supporting their functional specialization and possible activity mechanisms is examined. Finally, strategies are discussed for exploiting new and established technologies to overcome the difficulties posed by the multigene status of RCI2s and the integral membrane character of their proteins, enabling the probing of their individual functions and collective significance.

A novel rice calmodulin-like gene, OsMSR2, enhances drought and salt tolerance and increases ABA sensitivity in Arabidopsis.

Many abiotic stimuli, such as drought and salt stresses, elicit changes in intracellular calcium levels that serve to convey information and activate adaptive responses. Ca²âº signals are perceived by different Ca²âº sensors, and calmodulin (CaM) is one of the best-characterized Ca²âº sensors in eukaryotes. Calmodulin-like (CML) proteins also exist in plants, but their functions at the physiological and molecular levels are largely unknown. In this report, we present data on OsMSR2 (Oryza sativa L. Multi-Stress-Responsive gene 2), a novel calmodulin-like protein gene isolated from rice Pei'ai 64S (Oryza sativa L.). Expression of OsMSR2 was strongly up-regulated by a wide spectrum of stresses, including cold, drought, and heat in different tissues at different developmental stages of rice, as revealed by both microarray and quantitative real-time RT-PCR analyses. Analysis of the recombinant OsMSR2 protein demonstrated its potential ability to bind Ca²âº in vitro. Expression of OsMSR2 conferred enhanced tolerance to high salt and drought in Arabidopsis (Arabidopsis thaliana) accompanied by altered expression of stress/ABA-responsive genes. Transgenic plants also exhibited hypersensitivity to ABA during the seed germination and post-germination stages. The results suggest that expression of OsMSR2 modulated salt and drought tolerance in Arabidopsis through ABA-mediated pathways.

The Arabidopsis HOMOLOGY-DEPENDENT GENE SILENCING1 gene codes for an S-adenosyl-L-homocysteine hydrolase required for DNA methylation-dependent gene silencing.

Genes introduced into higher plant genomes can become silent (gene silencing) and/or cause silencing of homologous genes at unlinked sites (homology-dependent gene silencing or HDG silencing). Mutations of the HOMOLOGY-DEPENDENT GENE SILENCING1 (HOG1) locus relieve transcriptional gene silencing and methylation-dependent HDG silencing and result in genome-wide demethylation. The hog1 mutant plants also grow slowly and have low fertility and reduced seed germination. Three independent mutants of HOG1 were each found to have point mutations at the 3' end of a gene coding for S-adenosyl-l-homocysteine (SAH) hydrolase, and hog1-1 plants show reduced SAH hydrolase activity. A transposon (hog1-4) and a T-DNA tag (hog1-5) in the HOG1 gene each behaved as zygotic embryo lethal mutants and could not be made homozygous. The results suggest that the homozygous hog1 point mutants are leaky and result in genome demethylation and poor growth and that homozygous insertion mutations result in zygotic lethality. Complementation of the hog1-1 point mutation with a T-DNA containing the gene coding for SAH hydrolase restored gene silencing, HDG silencing, DNA methylation, fast growth, and normal seed viability. The same T-DNA also complemented the zygotic embryo lethal phenotype of the hog1-4 tagged mutant. A model relating the HOG1 gene, DNA methylation, and methylation-dependent HDG silencing is presented.