Submergence Treatment Research Articles

RNA-sequencing Analysis of Differentially Expressed Genes in Wild-type and BnERF -transgenic Arabidopsis Under Submergence Treatment

RNA-sequencing Analysis of Differentially Expressed Genes in Wild-type and <i>BnERF</i> -transgenic Arabidopsis Under Submergence Treatment

Analysis of functions of VIP1 and its close homologs in osmosensory responses of Arabidopsis thaliana.

VIP1 is a bZIP protein in Arabidopsis thaliana. VIP1 accumulates in the nucleus under hypo-osmotic conditions and interacts with the promoters of hypo-osmolarity-responsive genes, CYP707A1 and CYP707A3 (CYP707A1/3), but neither overexpression of VIP1 nor truncation of its DNA-binding region affects the expression of CYP707A3 in vivo, raising the possibility that VIP and other proteins are functionally redundant. Here we show further analyses on VIP1 and its close homologs, namely, Arabidopsis group I bZIP proteins. The patterns of the signals of the GFP-fused group I bZIP proteins were similar in onion and Arabidopsis cells, suggesting that they have similar subcellular localization. In a yeast one-hybrid assay, the group I bZIP proteins caused reporter gene activation in the yeast reporter strain. VIP1 and other group I bZIP proteins showed positive results in a yeast two-hybrid assay and a bimolecular fluorescence complementation assay, suggesting that they physically interact. These results support the idea that they have somewhat similar functions. By gel shift assays, VIP1-binding sequences in the CYP707A1/3 promoters were confirmed to be AGCTGT/G. Their presence in the promoters of the genes that respond to hypo-osmotic conditions was evaluated using previously published microarray data. Interestingly, a significantly higher proportion of the promoters of the genes that were up-regulated by rehydration treatment and/or submergence treatment (treatment by a hypotonic solution) and a significantly lower proportion of the promoters of the genes that were down-regulated by such treatment shared AGCTGT/G. To further assess the physiological role of VIP1, constitutively nuclear-localized variants of VIP1 were generated. When overexpressed in Arabidopsis, some of them as well as VIP1 caused growth retardation under a mannitol-stressed condition, where VIP1 is localized mainly in the cytoplasm. This raises the possibility that the expression of VIP1 itself rather than its nuclear localization is responsible for regulating the mannitol responses.

Morphological changes and resource allocation of Zizania latifolia (Griseb.) Stapf in response to different submergence depth and duration

Plants around ponds, rivers and lakes are subjected to long-term partial or complete submergence. When they are flooded, water level affects the plants simultaneously with duration of submergence. Separate and interactive effects of water level and duration on the growth of the herbaceous perennial Zizania latifolia (Poaceae) were investigated by exposing the plants in greenhouse water tanks to submergence in different water depths and for different time-spans. The plants exhibited great shoot elongation upon submergence and prolonged flood duration, and the basal tiller number of the species decreased with higher water levels. Submergence treatment advanced the flowering date and increased the inflorescence number. Plant total biomass did not differ among all the treatments, while the root:shoot ratio decreased with increased water level, prolonged duration of submergence and their interaction. The high plasticity in morphology and shifts in reproductive strategy and biomass allocation enabled the Zizania plants to survive the compound effect of flooding height and duration. This may explain the occurrence of this species in habitats subjected to long-term flooding. The results obtained in this experiment will contribute to understanding the impact of flooding dynamics on plants and the ways of adaptation responses to prolonged waterlogging.

Photoinhibition-like damage to the photosynthetic apparatus in plant leaves induced by submergence treatment in the dark.

Submergence is a common type of environmental stress for plants. It hampers survival and decreases crop yield, mainly by inhibiting plant photosynthesis. The inhibition of photosynthesis and photochemical efficiency by submergence is primarily due to leaf senescence and excess excitation energy, caused by signals from hypoxic roots and inhibition of gas exchange, respectively. However, the influence of mere leaf-submergence on the photosynthetic apparatus is currently unknown. Therefore, we studied the photosynthetic apparatus in detached leaves from four plant species under dark-submergence treatment (DST), without influence from roots and light. Results showed that the donor and acceptor sides, the reaction center of photosystem II (PSII) and photosystem I (PSI) in leaves were significantly damaged after 36 h of DST. This is a photoinhibition-like phenomenon similar to the photoinhibition induced by high light, as further indicated by the degradation of PsaA and D1, the core proteins of PSI and PSII. In contrast to previous research, the chlorophyll content remained unchanged and the H2O2 concentration did not increase in the leaves, implying that the damage to the photosynthetic apparatus was not caused by senescence or over-accumulation of reactive oxygen species (ROS). DST-induced damage to the photosynthetic apparatus was aggravated by increasing treatment temperature. This type of damage also occurred in the anaerobic environment (N2) without water, and could be eliminated or restored by supplying air to the water during or after DST. Our results demonstrate that DST-induced damage was caused by the hypoxic environment. The mechanism by which DST induces the photoinhibition-like damage is discussed below.

Root transcript profiling of two Rorippa species reveals gene clusters associated with extreme submergence tolerance.

Complete submergence represses photosynthesis and aerobic respiration, causing rapid mortality in most terrestrial plants. However, some plants have evolved traits allowing them to survive prolonged flooding, such as species of the genus Rorippa, close relatives of Arabidopsis (Arabidopsis thaliana). We studied plant survival, changes in carbohydrate and metabolite concentrations, and transcriptome responses to submergence of two species, Rorippa sylvestris and Rorippa amphibia. We exploited the close relationship between Rorippa species and the model species Arabidopsis by using Arabidopsis GeneChip microarrays for whole-genome transcript profiling of roots of young plants exposed to a 24-h submergence treatment or air. A probe mask was used based on hybridization of genomic DNA of both species to the arrays, so that weak probe signals due to Rorippa species/Arabidopsis mismatches were removed. Furthermore, we compared Rorippa species microarray results with those obtained for roots of submerged Arabidopsis plants. Both Rorippa species could tolerate deep submergence, with R. sylvestris surviving much longer than R. amphibia. Submergence resulted in the induction of genes involved in glycolysis and fermentation and the repression of many energy-consuming pathways, similar to the low-oxygen and submergence response of Arabidopsis and rice (Oryza sativa). The qualitative responses of both Rorippa species to submergence appeared roughly similar but differed quantitatively. Notably, glycolysis and fermentation genes and a gene encoding sucrose synthase were more strongly induced in the less tolerant R. amphibia than in R. sylvestris. A comparison with Arabidopsis microarray studies on submerged roots revealed some interesting differences and potential tolerance-related genes in Rorippa species.

Submergence confers immunity mediated by the WRKY22 transcription factor in Arabidopsis.

Transcriptional control plays an important role in regulating submergence responses in plants. Although numerous genes are highly induced during hypoxia, their individual roles in hypoxic responses are still poorly understood. Here, we found that expression of genes that encode members of the WRKY transcription factor family was rapidly and strongly induced upon submergence in Arabidopsis thaliana, and this induction correlated with induction of a large portion of innate immunity marker genes. Furthermore, prior submergence treatment conferred higher resistance to the bacterial pathogen Pseudomonas syringae in Arabidopsis. Among the WRKY genes tested, WRKY22 had the highest level of induction during the early stages of submergence. Compared with the wild type, WRKY22 T-DNA insertion mutants wrky22-1 and wrky22-2 had lower disease resistance and lower induction of innate immunity markers, such as FLG22-INDUCED RECEPTOR-LIKE KINASE1 (FRK1) and WRKY53, after submergence. Furthermore, transcriptomic analyses of wrky22-2 and chromatin immunoprecipitation identified several potential targets of WRKY22, which included genes encoding a TIR domain-containing protein, a plant peptide hormone, and many OLIGO PEPTIDE TRANSPORTER genes, all of which may lead to induction of innate immunity. In conclusion, we propose that submergence triggers innate immunity in Arabidopsis via WRKY22, a response that may protect against a higher probability of pathogen infection either during or after flooding.

Effects of complete submergence on seedling growth and survival of five riparian tree species in the warm-temperate regions of Japan

To reveal the relationship between tolerance to submergence and the distribution ranges of riparian tree species in the floodplains of the warm-temperate regions in Japan, we assessed the response and tolerance of current-year seedlings of two Salix and three Ulmaceae species to submergence treatments for 1, 2, 4, and 8 weeks. We investigated shoot elongation, number of leaves, and survival rate of seedlings during the experiment, and biomass allocation was determined at the end of the experiment. Shoot elongation and leaf production of seedlings were suppressed in all the species during the submergence treatments. However, the seedlings of Salix chaenomeloides and S. pierotii elongated shoots rapidly and produced leaves after the treatments. All the underground biomass in these two species was larger than aboveground biomass. These results are considered as typical responses of flood-tolerant species. In contrast, the underground biomass of Ulmaceae seedlings (Celtis sinensis var. japonica, Aphananthe aspera, and Ulmus parvifolia) decreased more rapidly than aboveground biomass during prolonged submergence. Furthermore, A. aspera seedlings also showed suppression of shoot elongation and leaf production after the treatments. Our results indicate that the three Ulmaceae species are less tolerant to submergence than the two Salix species. In conclusion, we suggest that submergence stress is one of the important factors determining the distribution of tree species in the floodplains of lowlands in the warm-temperate regions of Japan.

Identification of SUB1A alleles from wild rice Oryza rufipogon Griff.

Submergence stress is a major constraint to rice production in South and Southeast Asia. Most rice (Oryza sativa L.) cultivars die within a week of complete submergence, while a small number of accessions are submergence-tolerant for up to 2 weeks or more. These cultivars have the tolerant allele of the SUB1A gene, one of three ERF genes at this locus on rice chromosome 9. In all O. sativa varieties studied, the SUB1A gene is limited to a subset of indica accessions of O. sativa. Thus far, there has been no published report of the SUB1A gene in wild rice species. Here we report evidence of the SUB1A gene found in wild species of O. rufipogon Griff. accessions by the use of degenerate primers corresponding to the most highly conserved regions of the SUB1 locus. The results indicated that two SUB1A-like alleles, e.g. OrSub1A-1 and OrSub1A-2, were identified from two O. rufipogon accessions. Submergence treatment shows that both of the accessions with SUB1A-like genes were submergence-intolerant. This preliminary study provides insight into the origin and allelic variation of SUB1A, an agronomically important gene that is rapidly being introduced into widely-grown rice cultivars.

Effects of simulated submergence on survival and recovery growth of three species in water fluctuation zone of the Three Gorges reservoir

Paspalum distichum, Cynodon dactylon and Hemarthria altissima distribute widely in natural water fluctuation zone of the Three Gorges region. To investigate whether they are suitable for growing in the artificial water fluctuation zone, which has longer submergence time and different submergence rhythm, of the Three Gorges reservoir, three complete submergence depths (0.5, 1 and 2 m) were conducted for about 6 months (from 12 November 2007 to 30 April 2008), and the survival and recovery growth of the three species were recorded after re-emergence for two weeks. The three species could start recovery growth within one week and more than 50% plants could survive. Among the three species, P. distichum had the largest increments in branch number and maximum stem length, and the smallest root shoot ratio. C. dactylon, however, had the smallest maximum stem length increment, and its survival and branch number increment were both larger than those of H. altissima. For C. dactylon and H. altissima, the survival and branch number increment significantly increased, while maximum stem length increment tended to decrease when submergence depth went higher. For P. distichum, the survival and the shoot mass were the lowest after 2 m submergence depth, but the other parameters were not different among different submergence treatments. Compared with control plants, submergence increased root shoot ratio of C. dactylon and H. altissima, but did not affect that of P. distichum. These results demonstrated that the three species are submergence-tolerant and can be applied in vegetation reconstruction in water fluctuation zone of the Three Gorges reservoir. Meanwhile, the results also suggested that the three species developed different survival tactics during the long-term submergence.

A kinetic analysis of hyponastic growth and petiole elongation upon ethylene exposure in Rumex palustris.

Complete submergence is an important stress factor for many terrestrial plants, and a limited number of species have evolved mechanisms to deal with these conditions. Rumex palustris is one such species and manages to outgrow the water, and thus restore contact with the atmosphere, through upward leaf growth (hyponasty) followed by strongly enhanced petiole elongation. These responses are initiated by the gaseous plant hormone ethylene, which accumulates inside plants due to physical entrapment. This study aimed to investigate the kinetics of ethylene-induced leaf hyponasty and petiole elongation. Leaf hyponasty and petiole elongation was studied using a computerized digital camera set-up followed by image analyses. Linear variable displacement transducers were used for fine resolution monitoring and measurement of petiole growth rates. We show that submergence-induced hyponastic growth and petiole elongation in R. palustris can be mimicked by exposing plants to ethylene. The petiole elongation response to ethylene is shown to depend on the initial angle of the petiole. When petiole angles were artificially kept at 0 degrees, rather than the natural angle of 35 degrees, ethylene could not induce enhanced petiole elongation. This is very similar to submergence studies and confirms the idea that there are endogenous, angle-dependent signals that influence the petiole elongation response to ethylene. Our data suggest that submergence and ethylene-induced hyponastic growth and enhanced petiole elongation responses in R. palustris are largely similar. However, there are some differences that may relate to the complexity of the submergence treatment as compared with an ethylene treatment.

Photosynthetic acclimation is important for post-submergence recovery of photosynthesis and growth in two riparian species.

Concomitant increases in O(2) and irradiance upon de-submergence can cause photoinhibition and photo-oxidative damage to the photosynthetic apparatus of plants. As energy and carbohydrate supply from photosynthesis is needed for growth, it was hypothesized that post-submergence growth recovery may require efficient photosynthetic acclimation to increased O(2) and irradiance to minimize photo-oxidative damage. The hypothesis was tested in two flood-tolerant species: a C(3) herb, Alternanthera philoxeroides; and a C(4) grass, Hemarthria altissima. The impact of low O(2) and low light, typical conditions in turbid floodwater, on post-submergence recovery was assessed by different flooding treatments combined with shading. Experiments were conducted during 30 d of flooding (waterlogging or submergence) with or without shading and subsequent recovery of 20 d under growth conditions. Changes in dry mass, number of branches/tillers, and length of the longest internodes and main stems were recorded to characterize growth responses. Photosynthetic parameters (photosystem II efficiency and non-photochemical quenching) were determined in mature leaves based on chlorophyll a fluorescence measurements. In both species growth and photosynthesis recovered after the end of the submergence treatment, with recovery of photosynthesis (starting shortly after de-submergence) preceding recovery of growth (pronounced on days 40-50). The effective quantum yield of photosystem II and non-photochemical quenching were diminished during submergence but rapidly increased upon de-submergence. Similar changes were found in all shaded plants, with or without flooding. Submerged plants did not suffer from photoinhibition throughout the recovery period although their growth recovery was retarded. After sudden de-submergence the C(3) plant A. philoxeroides and the C(4) plant H. altissima were both able to maintain the functionality of the photosynthetic apparatus through rapid acclimation to changing O(2) and light conditions. The ability for photosynthetic acclimation may be essential for adaptation to wetland habitats in which water levels fluctuate.

OsBADH1 is possibly involved in acetaldehyde oxidation in rice plant peroxisomes

Although rice (Oryza sativa L.) produces little glycine betaine (GB), it has two betaine aldehyde dehydrogenase (BADH; EC 1.2.1.8) gene homologs (OsBADH1 and OsBADH2). We found that OsBADH1 catalyzes the oxidation of acetaldehyde efficiently, while the activity of OsBADH2 is extremely low. The accumulation of OsBADH1 mRNA decreases following submergence treatment, but quickly recovers after re-aeration. We confirmed that OsBADH1 localizes in peroxisomes. In this paper, a possible physiological function of OsBADH1 in the oxidation of acetaldehyde produced by catalase in rice plant peroxisomes is discussed.

Effects of total submergence in saltwater on growth and leaf ion content of preflooded and unflooded Taxodium distichum saplings

Preconditioning by hypoxic condition would contribute higher tolerance to anoxic condition in physiological and metabolic aspects of various plant species. In expectation of improvement of salinity tolerance, effects of preconditioning with soil flooding on growth responses and photosynthetic activity in relation to Na+ content in leaves and roots were studied using 2-year-old Taxodium distichum saplings. A submergence experiment was performed at three salt concentrations (0, 4000, and 8000 ppm NaCl), and preconditioning was started 2 months prior to the beginning of submergence treatments. Continuous soil flooding with freshwater as a control did not inhibit growth in height and stimulated diameter increment of the saplings. Saplings submerged in saltwater and freshwater also showed no morphological changes during submergence treatments. However, leaf injury and shoot dieback were observed in drained saplings that had been submerged in saltwater. Na+ and K+ ion contents increased with increases in salt concentration in both preconditioned and unconditioned saplings, whereas ion contents in preconditioned saplings tended to be higher than those of unconditioned saplings.

Is elongation-induced leaf emergence beneficial for submerged Rumex species?

Plant species from various taxa 'escape' from low oxygen conditions associated with submergence by a suite of traits collectively called the low oxygen escape syndrome (LOES). The expression of these traits is associated with costs and benefits. Thus far, remarkably few studies have dealt with the expected benefits of the LOES. Young plants were fully submerged at initial depths of 450 mm (deep) or 150-240 mm (shallow). Rumex palustris leaf tips emerged from the shallow flooding within a few days, whereas a slight lowering of shallow flooding was required to expose R. acetosa leaf tips to the atmosphere. Shoot biomass and petiole porosity were measured for all species, and treatments and data from the deep and shallow submergence treatments were compared with non-flooded controls. R. palustris is characterized by submergence-induced enhanced petiole elongation. R. acetosa lacked this growth response. Upon leaf tip emergence, R. palustris increased its biomass, whereas R. acetosa did not. Furthermore, petiole porosity in R. palustris was twice as high as in R. acetosa. Leaf emergence restores gas exchange between roots and the atmosphere in R. palustris. This occurs to a much lesser extent in R. acetosa and is attributable to its lower petiole porosity and therefore limited internal gas transport. Leaf emergence resulting from fast petiole elongation appears to benefit biomass accumulation if these plants contain sufficient aerenchyma in petioles and roots to facilitate internal gas exchange.

Chlorophyll fluorescence parameters, CO 2 photosynthetic rate and regeneration capacity as a result of complete submergence and subsequent re-emergence in rice ( Oryza sativa L.)

Regeneration capacity of submerged rice ( Oryza sativa) seedlings in terms of CO 2 photosynthetic rate, chlorophyll a fluorescence and chlorophyll and carbohydrate content were investigated in three Indica rice cultivars namely FR 13A, Kalaputia and IR 42 that differed in submergence tolerance. Twenty-one day old plants were completely submerged under water for 8 days. Subsequently, plants were kept under normal conditions with 5–10 cm of stagnant water above soil surface for a further period of 15 days. After complete submergence, all genotypes showed inhibition of CO 2 photosynthetic rate. Submergence treatment resulted in a significant reduction of Rubisco activity. Maximal photochemical efficiency ( F v/ F m) of PS II and area above the fluorescence curve between F o and F m decreased more under submergence especially in susceptible cultivar IR 42. When re-aerated, the plants recovered to various degrees. The carbohydrate content of plants was found to be significantly and positively associated with submergence tolerance and regeneration growth. The tolerant cultivar (FR 13A) could survive submergence apparently because it possessed 1.9–2.0 and 3.2–3.7-fold more non-structural carbohydrate content before and after submergence compared to the susceptible cultivar (IR 42) and it had a better capability to restore its photosynthetic capacity during post-submergence periods.

Isolation of a maize beta-glucosidase gene promoter and characterization of its activity in transgenic tobacco

The beta-glucosidase gene of maize (ZmGLU1) was suggested to hydrolyze cytokinin-conjugate and release free cytokinin during plant growth and development. A clone containing the upstream region of ZmGLU1 was isolated and sequenced from a maize genomic library. The full-length ZmGLU1 promoter and a series of its 5' deletions were fused to the beta-glucuronidase (GUS) reporter gene and transferred into tobacco. The GUS activity of transgenic plants was assayed at various developmental stages. The results showed that ZmGLU1 promoter-driven GUS gene had the highest expression level in the roots and that the expression of GUS gene declined during seed maturation and down to the lowest level in mature seeds. The ZmGLU1 promoter-driven GUS expression increased during seed germination, reaching a peak on day 11. The results also showed that this promoter could be inhibited by 6-BA, trans-zeatin, and NAA, but was not affected by GA(3), ABA, SA, cold, salt, drought, and submergence treatments. The histochemical staining revealed that GUS activity was located in vigorous cell division zones with dominant staining associated with vascular tissues. Deletion analysis showed that the promoter contained a putative leaf-specific and stem-specific negative regulative element and two putative enhancers.

Revelation on early response and molecular mechanism of submergence tolerance in maize roots by microarray and suppression subtractive hybridization

Submergence stress results in oxygen limitation in maize roots. Studying differential gene expression pattern in comparison submergence-tolerance lines with non-tolerant lines is critical for discovering genes associated with submergence tolerance and elucidating the mechanism of submergence tolerance. In this study, two inbred with difference of tolerance, Mo17 and Hz32, were used to reveal early responsive genes in root cells under submerging condition. Suppression subtracted hybridization (SSH) and cDNA microarray experiments showed that a number of gene expressions were altered because of submergence treatment. These genes are involved in a broad spectrum of biochemical, cellular, and physiological processes, such as glycolysis, energy metabolism, lipid metabolism, signal conduction, DNA transcription, protein biosynthesis and digestion, cell component and photosynthesis. The spectrum of genes in the first 0.5 h of treatment was significantly different from that of the genes induced later 2–4 h. In addition, changes of gene expression in responses to submerging were different in the two inbred lines. Four transcription factors were expressed at different profile in Hz32 and Mo17. The metabolic and physiological conversions from aerobic to anaerobic condition were faster in Hz32 than that in Mo17. Based on the responsive genes and their functions, we propose that early response of maize roots to submergence stress may be a complex network involving multiple physiological and metabolic pathways, and regulation of transcriptional processes plays a critical role in metabolic adaptation of maize roots during early stages of submergence.

Vitreoscilla hemoglobin overexpression increases submergence tolerance in cabbage

Agrobacterium tumefaciens was used to deliver the vhb gene into cabbage (Brassica oleracea var. Cabitata) cv. Xiaguang's parent line, 103. Using hypocotyls and cotyledon petioles as explants for infection, we obtained a transformation efficiency of 3-5% based on the number of transgenic shoots produced from the number of explants used for infection. Molecular analysis indicated that the vhb gene was stably integrated into the cabbage genome and that the vhb gene was expressed at the RNA level. Characterization of the vhb over-expressing transgenic plants revealed that transgenic seeds germinated faster than the wildtype controls. More importantly, the transgenic plants showed tolerance to a prolonged submergence treatment, suggesting that the vhb gene may provide an excellent tool for creation of submergence/flooding-tolerant cultivars of agriculturally important crops.

Dynamic aspects of alcoholic fermentation of rice seedlings in response to anaerobiosis and to complete submergence: relationship to submergence tolerance.

Rice plants are severely damaged by complete submergence. This is a problem in rice farming and could be the result, in part, of tissue anoxia imposed by a reduced availability of oxygen. To investigate this possibility we monitored alcoholic fermentation products as markers for tissue anaerobiosis using sensitive laser-based spectroscopy able to sense ethanol and acetaldehyde down to 3 nl l(-1) and 0.1 nl l(-1), respectively. Acetaldehyde emission began within 0.5 h of imposing an oxygen-free gas phase environment followed closely by ethanol. As treatment progressed, ethanol output increased and came to exceed acetaldehyde emission as this stabilized considerably after approx. 3 h. On re-entry of air, a sharp post-anaerobic peak of acetaldehyde production was observed. This was found to be diagnostic of a preceding anoxic episode of 0.5 h or more. When anaerobiosis was lengthened by up to 14 h, the size of the post-anaerobic acetaldehyde outburst increased. After de-submergence from oxygen-free water, a similarly strong but slower post-anaerobic acetaldehyde upsurge was seen, which was accompanied by an increase in ethanol emission. Light almost, but not completely, eliminated fermentation in anaerobic surroundings and also the post-anaerobic or post-submergence peaks in acetaldehyde production. All photosynthetically generated oxygen was consumed within the plant. There was no substantial difference in acetaldehyde and ethanol output between FR13A and the less submergence-tolerant line CT6241 under any submergence treatment. In some circumstances, submergence damaged CT6241 more than FR13A even in the absence of vigorous fermentation. We conclude that oxygen deprivation may not always determine the extent of damage caused to rice plants by submergence under natural conditions.

The novel ethylene-regulated gene OsUsp1 from rice encodes a member of a plant protein family related to prokaryotic universal stress proteins.

Using subtractive hybridization a submergence-induced gene was identified from deepwater rice, OsUsp1, that encodes a homologue of the bacterial universal stress protein family. Sequence analysis revealed that OsUSP1 is most closely related to the bacterial MJ0577-type of ATP-binding USP proteins which have been suggested to act as a molecular switch. USP protein homologues appear to be ubiquitous in plants and are encoded by gene families, but are absent in animal species. In the youngest internode of deepwater rice plants, OsUsp1 expression was very strongly induced within 1 h of submergence. Elevated transcript levels were observed in dividing cells, in expanding cells and in differentiated tissue indicating that USP1 mediates a general process. Gene induction was shown to be regulated by ethylene with a highly similar expression pattern to that observed with submergence treatment. Based on sequence information and on expression data it is hypothesized that OsUSP1 plays a role in ethylene-mediated stress adaptation in rice.