Overexpression of the RADICAL-INDUCED CELL DEATH1 (RCD1) gene of Arabidopsis causes weak rcd1 phenotype with compromised oxidative-stress responses

Integrated Analysis of miRNAs Associated With Sugarcane Responses to Low-Potassium Stress

Sugarcane is among the most important global crops and a key bioenergy source. Sugarcane production is restricted by limited levels of available soil potassium (K⁺). The ability of plants to respond to stressors can be regulated by a range of microRNAs (miRNAs). However, there have been few studies regarding the roles of miRNAs in the regulation of sugarcane responses to K⁺-deficiency. To understand how these non-coding RNAs may influence sugarcane responses to low-K⁺ stress, we conducted expression profiling of miRNAs in sugarcane roots under low-K⁺ conditions via high-throughput sequencing. This approach led to the identification of 324 and 42 known and novel miRNAs, respectively, of which 36 were found to be differentially expressed miRNAs (DEMs) under low-K⁺ conditions. These results also suggested that miR156-x/z and miR171-x are involved in these responses as potential regulators of lateral root formation and the ethylene signaling pathway, respectively. A total of 705 putative targets of these DEMs were further identified through bioinformatics predictions and degradome analyses, and GO and KEGG enrichment analyses revealed these target mRNAs to be enriched for catalytic activity, binding functions, metabolic processes, plant hormone signal transduction, and mitogen-activated protein kinase (MAPK) signaling. In summary, these data provide an overview of the roles of miRNAs in the regulation of sugarcane response to low-K⁺ conditions.

Isolation and Identification of Ipomoea cairica (L.) Sweet Gene IcSRO1 Encoding a SIMILAR TO RCD-ONE Protein, Which Improves Salt and Drought Tolerance in Transgenic Arabidopsis

Ipomoea cairica is a tropical plant and a wild relative of the food plant sweet potato (Ipomoea batatas), listed as one of the most invasive alien species in China. Recently, it has been reported that I. cairica had successfully invaded mangrove wetlands, indicating its high salt tolerance. Based on previous genetic studies, I. cairica offers a good model for characterizing stress-resistant genes. It has recently been identified that the SRO proteins (SIMILAR TO RCD-ONE) play important roles in a variety of stress and developmental responses. Radical-Induced Cell Death1 (RCD1) was the first identified plant SRO protein from Arabidopsis thaliana. As a typical SRO protein, IcSRO1 had a highly conservative WWE domain, a conserved PARP fold and protein C in the RST function area. The expression of IcSRO1 was induced by salt, drought, and the plant hormone ABA. The transgenic Arabidopsis overexpressing IcSRO1 showed higher tolerance against salt and drought stress along with lower accumulation of hydrogen peroxide (H₂O₂) and superoxide (O₂^-) than the wild type. The IcSRO1 protein was localized in the nucleus after cultivation in the buffer. Our results indicated it could interact with Arabidopsis SALT OVERLY SENSITIVE 1 (AtSOS1), suggesting IcSRO1 may have similar functions. The pleiotropic effect of IcSRO1 on physiological processes contributes to the improvement of plant tolerance against diverse abiotic stresses, and may be associated with the adaptation of I. cairica to those environments with extreme saline and drought conditions. It therefore provides valuable gene resources for crop breeding enhancement.

Poly(ADP-Ribose) Polymerases in Plants and Their Human Counterparts: Parallels and Peculiarities

Poly(ADP-ribosyl)ation is a rapid and transient post-translational protein modification that was described first in mammalian cells. Activated by the sensing of DNA strand breaks, poly(ADP-ribose)polymerase1 (PARP1) transfers ADP-ribose units onto itself and other target proteins using NAD⁺ as a substrate. Subsequently, DNA damage responses and other cellular responses are initiated. In plants, poly(ADP-ribose) polymerases (PARPs) have also been implicated in responses to DNA damage. The Arabidopsis genome contains three canonical PARP genes, the nomenclature of which has been uncoordinated in the past. Albeit assumptions concerning the function and roles of PARP proteins in planta have often been inferred from homology and structural conservation between plant PARPs and their mammalian counterparts, plant-specific roles have become apparent. In particular, PARPs have been linked to stress responses of plants. A negative role under abiotic stress has been inferred from studies in which a genetic or, more commonly, pharmacological inhibition of PARP activity improved the performance of stressed plants; in response to pathogen-associated molecular patterns, a positive role has been suggested. However, reports have been inconsistent, and the effects of PARP inhibitors appear to be more robust than the genetic abolition of PARP gene expression, indicating the presence of alternative targets of those drugs. Collectively, recent evidence suggests a conditionality of stress-related phenotypes of parp mutants and calls for a reconsideration of PARP inhibitor studies on plants. This review critically summarizes our current understanding of poly(ADP-ribosylation) and PARP proteins in plants, highlighting similarities and differences to human PARPs, areas of controversy, and requirements for future studies.

OsSRO1a Interacts with RNA Binding Domain-Containing Protein (OsRBD1) and Functions in Abiotic Stress Tolerance in Yeast

SRO1 is an important regulator of stress and hormonal response in plants and functions by interacting with transcription factors and several other proteins involved in abiotic stress response. In the present study, we report OsRBD1, an RNA binding domain 1- containing protein as a novel interacting partner of OsSRO1a from rice. The interaction of OsSRO1a with OsRBD1 was shown in yeast as well as in planta. Domain-domain interaction study revealed that C-terminal RST domain of OsSRO1a interacts with the N-terminal RRM1 domain of OsRBD1 protein. Both the proteins were found to co-localize in nucleus. Transcript profiling under different stress conditions revealed co-regulation of OsSRO1a and OsRBD1 expression under some abiotic stress conditions. Further, co-transformation of both OsSRO1a and OsRBD1 in yeast conferred enhanced tolerance toward salinity, osmotic, and methylglyoxal treatments. Our study suggests that the interaction of OsSRO1a with OsRBD1 confers enhanced stress tolerance in yeast and may play an important role under abiotic stress responses in plants.

Overexpression of AtSTO1 leads to improved salt tolerance in Populus tremula × P. alba

One of the major abiotic stress conditions limiting healthy growth of trees is salinity stress. The use of gene manipulation for increased tolerance to abiotic stress has been successful in many plant species. Overexpression of the Arabidopsis SALT TOLERANT1 (STO1) gene leads to increased concentrations of 9-cis-epoxycarotenoid dioxygenase3, a vital enzyme in Arabidopsis abscisic acid biosynthesis. In the present work, the Arabidopsis STO1 gene (AtSTO1) was overexpressed in poplar to determine if the transgene would confer enhanced salt tolerance to the generated transgenics. The results of multiple greenhouse trials indicated that the transgenic poplar lines had greater levels of resistance to NaCl than wild-type plants. Analysis using RT-PCR indicated a variation in the relative abundance of the STO1 transcript in the transgenics that coincided with tolerance to salt. Several physiological and morphological changes such as greater overall biomass, greater root biomass, improved photosynthesis, and greater pith size were observed in the transgenics when compared to controls undergoing salt stress. These results indicated overexpression of AtSTO1 improved salt tolerance in poplar.

The radical induced cell death protein 1 (RCD1) supports transcriptional activation of genes for chloroplast antioxidant enzymes

The rimb1 (redox imbalanced 1) mutation was mapped to the RCD1 locus (radical-induced cell death 1; At1g32230) demonstrating that a major factor involved in redox-regulation genes for chloroplast antioxidant enzymes and protection against photooxidative stress, RIMB1, is identical to the regulator of disease response reactions and cell death, RCD1. Discovering this link let to our investigation of its regulatory mechanism. We show in yeast that RCD1 can physically interact with the transcription factor Rap2.4a which provides redox-sensitivity to nuclear expression of genes for chloroplast antioxidant enzymes. In the rimb1 (rcd1-6) mutant, a single nucleotide exchange results in a truncated RCD1 protein lacking the transcription factor binding site. Protein-protein interaction between full-length RCD1 and Rap2.4a is supported by H2O2, but not sensitive to the antioxidants dithiotreitol and ascorbate. In combination with transcript abundance analysis in Arabidopsis, it is concluded that RCD1 stabilizes the Rap2.4-dependent redox-regulation of the genes encoding chloroplast antioxidant enzymes in a widely redox-independent manner. Over the years, rcd1-mutant alleles have been described to develop symptoms like chlorosis, lesions along the leaf rims and in the mesophyll and (secondary) induction of extra- and intra-plastidic antioxidant defense mechanisms. All these rcd1 mutant characteristics were observed in rcd1-6 to succeed low activation of the chloroplast antioxidant system and glutathione biosynthesis. We conclude that RCD1 protects plant cells from running into reactive oxygen species (ROS)-triggered programs, such as cell death and activation of pathogen-responsive genes (PR genes) and extra-plastidic antioxidant enzymes, by supporting the induction of the chloroplast antioxidant system.

The SNAC1-targeted gene OsSRO1c modulates stomatal closure and oxidative stress tolerance by regulating hydrogen peroxide in rice

Abiotic stresses such as drought cause a reduction of plant growth and loss of crop yield. Stomatal aperture controls CO(2) uptake and water loss to the atmosphere, thus playing important roles in both the yield gain and drought tolerance of crops. Here, a rice homologue of SRO (similar to RCD one), termed OsSRO1c, was identified as a direct target gene of SNAC1 (stress-responsive NAC 1) involved in the regulation of stomatal aperture and oxidative response. SNAC1 could bind to the promoter of OsSRO1c and activate the expression of OsSRO1c. OsSRO1c was induced in guard cells by drought stress. The loss-of-function mutant of OsSRO1c showed increased stomatal aperture and sensitivity to drought, and faster water loss compared with the wild-type plant, whereas OsSRO1c overexpression led to decreased stomatal aperture and reduced water loss. Interestingly, OsSRO1c-overexpressing rice showed increased sensitivity to oxidative stress. Expression of DST, a reported zinc finger gene negatively regulating H(2)O(2)-induced stomatal closure, and the activity of H(2)O(2)-scavenging related enzymes were significantly suppressed, and H(2)O(2) in guard cells was accumulated in the overexpression lines. OsSRO1c interacted with various stress-related regulatory and functional proteins, and some of the OsSRO1c-interacting proteins are predicted to be involved in the control of stomatal aperture and oxidative stress tolerance. The results suggest that OsSRO1c has dual roles in drought and oxidative stress tolerance of rice by promoting stomatal closure and H(2)O(2) accumulation through a novel pathway involving regulators SNAC1 and DST.

A transcriptomic analysis reveals the nature of salinity tolerance of a wheat introgression line

The bread wheat cultivar Shanrong No.3 (SR3) is a salinity tolerant derivative of an asymmetric somatic hybrid between cultivar Jinan 177 (JN177) and tall wheatgrass (Thinopyrum ponticum). To reveal some of the mechanisms underlying its elevated abiotic stress tolerance, both SR3 and JN177 were exposed to iso-osmotic NaCl and PEG stress, and the resulting gene expression was analysed using a customized microarray. Some genes associated with stress response proved to be more highly expressed in SR3 than in JN177 in non-stressed conditions. Its unsaturated fatty acid and flavonoid synthesis ability was also enhanced, and its pentose phosphate metabolism was more active than in JN177. These alterations in part accounted for the observed shift in the homeostasis related to reactive oxygen species (ROS). The specific down-regulation of certain ion transporters after a 0.5 h exposure to 340 mM NaCl demonstrated that Na(+) uptake occurred rapidly, so that the early phase of salinity stress imposes more than simply an osmotic stress. We discussed the possible effect of the introgression of new genetic materials in wheat genome on stress tolerance.

The paralogous genes RADICAL-INDUCED CELL DEATH1 and SIMILAR TO RCD ONE1 have partially redundant functions during Arabidopsis development

RADICAL-INDUCED CELL DEATH1 (RCD1) and SIMILAR TO RCD ONE1 (SRO1) are the only two proteins encoded in the Arabidopsis (Arabidopsis thaliana) genome containing both a putative poly(ADP-ribose) polymerase catalytic domain and a WWE protein-protein interaction domain, although similar proteins have been found in other eukaryotes. Poly(ADP-ribose) polymerases mediate the attachment of ADP-ribose units from donor NAD(+) molecules to target proteins and have been implicated in a number of processes, including DNA repair, apoptosis, transcription, and chromatin remodeling. We have isolated mutants in both RCD1 and SRO1, rcd1-3 and sro1-1, respectively. rcd1-3 plants display phenotypic defects as reported for previously isolated alleles, most notably reduced stature. In addition, rcd1-3 mutants display a number of additional developmental defects in root architecture and maintenance of reproductive development. While single mutant sro1-1 plants are relatively normal, loss of a single dose of SRO1 in the rcd1-3 background increases the severity of several developmental defects, implying that these genes do share some functions. However, rcd1-3 and sro1-1 mutants behave differently in several developmental events and abiotic stress responses, suggesting that they also have distinct functions. Remarkably, rcd1-3; sro1-1 double mutants display severe defects in embryogenesis and postembryonic development. This study shows that RCD1 and SRO1 are at least partially redundant and that they are essential genes for plant development.

Identification of a novel tumor transforming gene GAEC1 at 7q22 which encodes a nuclear protein and is frequently amplified and overexpressed in esophageal squamous cell carcinoma

By comparative DNA fingerprinting, we identified a 357-bp DNA fragment frequently amplified in esophageal squamous cell carcinomas (ESCC). This fragment overlaps with an expressed sequence tag mapped to 7q22. Further 5' and 3'-rapid amplification of cDNA ends revealed that it is part of a novel, single-exon gene with full-length mRNA of 2052 bp and encodes a nuclear protein of 109 amino acids ( approximately 15 kDa). This gene, designated as gene amplified in esophageal cancer 1 (GAEC1), was located within a 1-2 Mb amplicon at 7q22.1 identified by high-resolution 1 Mb array-comparative genomic hybridization in 6/10 ESCC cell lines. GAEC1 was ubiquitously expressed in normal tissues including esophageal and gastrointestinal organs; with amplification and overexpression in 6/10 (60%) ESCC cell lines and 34/99 (34%) primary tumors. Overexpression of GAEC1 in 3T3 mouse fibroblasts caused foci formation and colony formation in soft agar, comparable to H-ras and injection of GAEC1-transfected 3T3 cells into athymic nude mice formed undifferentiated sarcoma in vivo, indicating that GAEC1 is a transforming oncogene. Although no significant correlation was observed between GAEC1 amplification and clinicopathological parameters and prognosis, our study demonstrated that overexpressed GAEC1 has tumorigenic potential and suggest that overexpressed GAEC1 may play an important role in ESCC pathogenesis.

Photosynthetic antenna size in higher plants is controlled by the plastoquinone redox state at the post-transcriptional rather than transcriptional level

We analyze the effect of the plastoquinone redox state on the regulation of the light-harvesting antenna size at transcriptional and post-transcriptional levels. This was approached by studying transcription and accumulation of light-harvesting complexes in wild type versus the barley mutant viridis zb63, which is depleted in photosystem I and where plastoquinone is constitutively reduced. We show that the mRNA level of genes encoding antenna proteins is almost unaffected in the mutant; this stability of messenger level is not a peculiarity of antenna-encoding genes, but it extends to all photosynthesis-related genes. In contrast, analysis of protein accumulation by two-dimensional PAGE shows that the mutant undergoes strong reduction of its antenna size, with individual gene products having different levels of accumulation. We conclude that the plastoquinone redox state plays an important role in the long term regulation of chloroplast protein expression. However, its modulation is active at the post-transcriptional rather than transcriptional level.