Physiological responses and Ethylene-Response AP2/ERF Factor expression in Indica rice seedlings subjected to submergence and osmotic stress.

BACKGROUND: The increased frequency of heavy rains in recent years has led to submergence stress in rice paddies, severely affecting rice production. Submergence causes not only hypoxic stress from excess water in the surrounding environment but also osmotic stress in plant cells. We assessed physiological responses and Ethylene-Response AP2/ERF Factor regulation under submergence conditions alone and with ionic or nonionic osmotic stress in submergence-sensitive IR64 and submergence-tolerant IR64-Sub1 Indica rice cultivars. RESULTS: Our results indicate that both IR64 and IR64-Sub1 exhibited shorter plant heights and root lengths under submergence with nonionic osmotic stress than normal condition and submergence alone. IR64-Sub1 seedlings exhibited a significantly lower plant height under submergence conditions alone and with ionic or nonionic osmotic stress than IR64 cultivars. IR64-Sub1 seedlings also presented lower malondialdehyde (MDA) concentration and higher survival rates than did IR64 seedlings after submergence with ionic or nonionic osmotic stress treatment. Sub1A-1 affects reactive oxygen species (ROS) accumulation and antioxidant enzyme activity in rice. The results also show that hypoxia-inducible ethylene response factors (ERF)-VII group and alcohol dehydrogenase 1 (ADH1) and lactate dehydrogenase 1 (LDH1) genes exhibited different expression levels under nonionic or ionic osmotic stress during submergence on rice. CONCLUSIONS: Together, these results demonstrate that complex regulatory mechanisms are involved in responses to the aforementioned forms of stress and offer new insights into the effects of submergence and osmotic stress on rice.

Assessment of Grain Harvest Moisture Content Using Machine Learning on Smartphone Images for Optimal Harvest Timing.

Grain moisture content (GMC) is a key indicator of the appropriate harvest period of rice. Conventional testing is time-consuming and laborious, thus not to be implemented over vast areas and to enable the estimation of future changes for revealing optimal harvesting. Images of single panicles were shot with smartphones and corrected using a spectral-geometric correction board. In total, 86 panicle samples were obtained each time and then dried at 80 °C for 7 days to acquire the wet-basis GMC. In total, 517 valid samples were obtained, in which 80% was randomly used for training and 20% was used for testing to construct the image-based GMC assessment model. In total, 17 GMC surveys from a total of 201 samples were also performed from an area of 1 m2 representing on-site GMC, which enabled a multi-day GMC prediction. Eight color indices were selected using principal component analysis for building four machine learning models, including random forest, multilayer perceptron, support vector regression (SVR), and multivariate linear regression. The SVR model with a MAE of 1.23% was the most suitable for GMC of less than 40%. This study provides a real-time and cost-effective non-destructive GMC measurement using smartphones that enables on-farm prediction of harvest dates and facilitates the harvesting scheduling of agricultural machinery.

Assessment of Rice Developmental Stage Using Time Series UAV Imagery for Variable Irrigation Management.

Rice is one of the three major crops in the world and is the major crop in Asia. Climate change and water resource shortages may result in decreases in rice yields and possible food shortage crises. In this study, water-saving farming management was tested, and IOT field water level monitoring was used to regulate water inflow automatically. Plant height (PH) is an important phenotype to be used to determine difference in rice growth periods and yields using water-saving irrigation. An unmanned aerial vehicle (UAV) with an RGB camera captured sequential images of rice fields to estimate rice PH compared with PH measured on site for estimating rice growth stages. The test results, with two crop harvests in 2019, revealed that with adequate image calibration, the correlation coefficient between UAV-PH and field-PH was higher than 0.98, indicating that UAV images can accurately determine rice PH in the field and rice growth phase. The study demonstrated that water-saving farming is effective, decreasing water usage for the first and second crops of 2019 by 53.5% and 21.7%, respectively, without influencing the growth period and final yield. Coupled with an automated irrigation system, rice farming can be adaptive to water shortage situations.

Comprehensive Transcriptomic Analysis of Auxin Responses in Submerged Rice Coleoptile Growth.

Cultivating rice in wet or water direct seeding systems is simple and time and labor efficient. Rice (Oryza sativa) seeds are a unique cereal that can germinate not only when submerged, but also in anoxic conditions. Many complicated hormone signals interact in submerged seed germination. Ethylene is involved in rice coleoptile elongation, but little is known regarding the role of auxin signaling under submergence. This study demonstrated that the coleoptile is shorter and curlier when submerged with 2,3,5-triiodobenzoic acid (TIBA). In transcriptomic analysis, 3448 of the 31,860 genes were upregulated, and 4360 genes were downregulated with submergence and TIBA treatment. The Gene Ontology function classification results demonstrated that upregulated differentially expressed genes (DEGs) were mainly involved in redox, stress, and signal transduction, whereas the down-regulated DEGs were mainly involved in RNA transcription, stress, and development. Furthermore, auxin signaling involved in the carbohydrate metabolism pathway was demonstrated while using transcriptomic analysis and confirmed in a quantitative real-time polymerase chain reaction. In addition, the transcript levels of development-related genes and mitochondria-electron- transport-related genes were regulated by auxin signaling under submergence. Auxin signaling was not only involved in regulating rice coleoptile elongation and development, but also regulated secondary metabolism, carbohydrate metabolism, and mitochondria electron transport under submergence. Our results presented that auxin signaling plays an important role during rice coleoptile elongation upon the submergence condition and improving the advance of research of direct rice seeding system.

Molecular Identification and Characterization of Hydroxycinnamoyl Transferase in Tea Plants (Camellia sinensis L.).

Tea (Camellia sinensis L.) contains abundant secondary metabolites, which are regulated by numerous enzymes. Hydroxycinnamoyl transferase (HCT) is involved in the biosynthesis pathways of polyphenols and flavonoids, and it can catalyze the transfer of hydroxyconnamoyl coenzyme A to substrates such as quinate, flavanol glycoside, or anthocyanins, thus resulting in the production of chlorogenic acid or acylated flavonol glycoside. In this study, the CsHCT gene was cloned from the Chin-Shin Oolong tea plant, and its protein functions and characteristics were analyzed. The full-length cDNA of CsHCT contains 1311 base pairs and encodes 436 amino acid sequences. Amino acid sequence was highly conserved with other HCTs from Arabidopsis thaliana, Populus trichocarpa, Hibiscus cannabinus, and Coffea canephora. Quantitative real-time polymerase chain reaction analysis showed that CsHCT is highly expressed in the stem tissues of both tea plants and seedlings. The CsHCT expression level was relatively high at high altitudes. The abiotic stress experiment suggested that low temperature, drought, and high salinity induced CsHCT transcription. Furthermore, the results of hormone treatments indicated that abscisic acid (ABA) induced a considerable increase in the CsHCT expression level. This may be attributed to CsHCT involvement in abiotic stress and ABA signaling pathways.

Analyzing organic tea certification and traceability system within the Taiwanese tea industry.

BACKGROUND: We applied game theory to the organic tea certification process and traceability system used by the Taiwanese tea industry to elucidate the strategic choices made by tea farmers and organic tea certification agencies. Thus, this paper clarifies how relevant variables affect the organic certification process and traceability system used within the tea industry. RESULTS: The findings indicate that farmers who generate high revenues experience failures regarding tea deliveries, cash outflow, damage compensation, and quasi-rent. An additional problem included the high costs yielded when tea farmers colluded with or switched organic tea certification agencies. Furthermore, there could be decreasing levels of personal interest in planting non-organic tea and lowering the costs of planting organic tea and the managerial accounting costs of building comprehensive traceability systems; thus, the analysis yielded strong results and a superior equilibrium. CONCLUSION: This research is unprecedented, using an innovative model and providing a novel analysis structure for use in the tea industry. These results contribute to the field of literature and should serve as a valuable reference for members of the tea industry, government, and academia.

Hydrogen peroxide controls transcriptional responses of ERF73/HRE1 and ADH1 via modulation of ethylene signaling during hypoxic stress.

Hypoxia, or oxygen deficiency, is an abiotic stress that plants are subjected to during soil flooding. Therefore, plants have evolved adaptive mechanisms to sense oxygen deficiency and make coordinated changes at the transcriptional level. The results of this study show that the interplay between hydrogen peroxide and ethylene affected the transcriptional responses of ERF73/HRE1 and ADH1 during hypoxia signaling. H2O2 affected the abundance of ERF73/HRE1 and ADH1 mRNAs in both wild-type Arabidopsis and the ethylene-insensitive mutant, ein2-5. Promoter analysis was conducted using transgenic plants expressing an ERF73/HRE1 promoter-ß-glucuronidase reporter gene construct. GUS staining observations and activity assays showed that GUS was regulated similarly to, and showed a similar accumulation pattern as, H2O2 during hypoxia. The transcript levels of ERF73/HRE1 and ADH1 were significantly decreased in the WT by combined hypoxia and diphenylene iodonium chloride (DPI, an NADPH oxidase inhibitor) treatment. In ein2-5, induction of ERF73/HRE1 was also reduced significantly by the combined hypoxia and DPI treatment. In contrast, ADH1 mRNA levels only slightly decreased after this treatment. When DPI was supplied at different time points during hypoxia treatment, H2O2 had critical effects on regulating the transcript levels of ERF73/HRE1 and ADH1 during the early stages of hypoxia signaling. The induction of hypoxia-inducible genes encoding peroxidases and cytochrome P450s was affected, and accumulation of H2O2 was reduced, in ein2-5 during hypoxic stress. Together, these results demonstrate that H2O2 plays an important role during primary hypoxia signaling to control the transcriptional responses of ERF73/HRE1 and ADH1 via modulation of ethylene signaling.

Integrative pathway and network analysis provide insights on flooding-tolerance genes in soybean.

Soybean is highly sensitive to flooding and extreme rainfall. The phenotypic variation of flooding tolerance is a complex quantitative trait controlled by many genes and their interaction with environmental factors. We previously constructed a gene-pool relevant to soybean flooding-tolerant responses from integrated multiple omics and non-omics databases, and selected 144 prioritized flooding tolerance genes (FTgenes). In this study, we proposed a comprehensive framework at the systems level, using competitive (hypergeometric test) and self-contained (sum-statistic, sum-square-statistic) pathway-based approaches to identify biologically enriched pathways through evaluating the joint effects of the FTgenes within annotated pathways. These FTgenes were significantly enriched in 36 pathways in the Gene Ontology database. These pathways were related to plant hormones, defense-related, primary metabolic process, and system development pathways, which plays key roles in soybean flooding-induced responses. We further identified nine key FTgenes from important subnetworks extracted from several gene networks of enriched pathways. The nine key FTgenes were significantly expressed in soybean root under flooding stress in a qRT-PCR analysis. We demonstrated that this systems biology framework is promising to uncover important key genes underlying the molecular mechanisms of flooding-tolerant responses in soybean. This result supplied a good foundation for gene function analysis in further work.

The AP2/ERF transcription factor AtERF73/HRE1 modulates ethylene responses during hypoxia in Arabidopsis.

A number of APETALA2 (AP2)/ETHYLENE RESPONSE FACTOR (ERF) genes have been shown to function in abiotic and biotic stress responses, and these genes are often induced by multiple stresses. We report here the characterization of an AP2/ERF gene in Arabidopsis (Arabidopsis thaliana) that is specifically induced during hypoxia. We show that under normoxic conditions, the expression of AtERF73/HRE1 can be induced by exogenous addition of 1-aminocyclopropane-1-carboxylic acid and that a combination of hypoxia and 1-aminocyclopropane-1-carboxylic acid results in hyperinduction of AtERF73/HRE1 expression. In addition, hypoxic induction of AtERF73/HRE1 is reduced but not completely abolished in ethylene-insensitive mutants and in the presence of inhibitors of ethylene biosynthesis and responses. These results suggest that, in addition to ethylene, an ethylene-independent signal is also required to mediate hypoxic induction of AtERF73/HRE1. To assess the role of AtERF73/HRE1, we generated three independent RNA interference (RNAi) knockdown lines of AtERF73/HRE1. Under normoxic conditions, the AtERF73/HRE1-RNAi seedlings displayed increased ethylene sensitivity and exaggerated triple responses, indicating that AtERF73/HRE1 might play a negative regulatory role in modulating ethylene responses. Gas chromatography analyses showed that the production of ethylene was similar between wild-type and RNAi lines under hypoxia. Quantitative reverse transcription-polymerase chain reaction analyses showed that hypoxia-inducible genes could be affected by AtERF73/HRE1-RNAi lines in two different ways: hypoxic induction of glycolytic and fermentative genes was reduced, whereas induction of a number of peroxidase and cytochrome P450 genes was increased. Taken together, our results show that AtERF73/HRE1 is involved in modulating ethylene responses under both normoxia and hypoxia.

Molecular characterization of polyphenol oxidase between small and large leaf tea cultivars.

Tea is a widely consumed beverage prepared using the fresh leaves of Camellia sinensis L. Tea plants are classified into small- and large-leaf varieties. Polyphenol oxidase (PPO), a crucial enzyme in tea manufacturing, catalyzes essential phenolic metabolites into different derivatives. To compare the molecular characteristics of CsPPO between cultivars, we cloned the full-length sequence of CsPPO cDNA from four representative tea cultivars in Taiwan. Amino acid sequence alignment analyses indicated that CsPPO is highly conserved. PPO exhibited similar enzymatic activity in different tea cultivars. Quantitative real-time polymerase chain reaction revealed no significant differences in the CsPPO transcript level between the small- and large-leaf varieties. However, tea harvested in summer and from low-altitude areas had a higher CsPPO transcript level than that harvested in winter and from high-altitude areas. Regulation of CsPPO by temperature was more significant in the small-leaf variety than in the large-leaf variety. The content of flavonoids and the expression of chalcone synthase, anthocyanidin synthase, and anthocyanidin reductase genes involved in the tea flavonoid biosynthesis pathway were higher in the large-leaf than in the small-leaf varieties, suggesting that the large-leaf variety had a higher antioxidative capacity than did the small-leaf variety. Our study compared the molecular properties of CsPPO between two tea varieties and clarified the physiological role of PPO in tea.

Controlling the lodging risk of rice based on a plant height dynamic model.

BACKGROUND: Rice is a key global food crop. Rice lodging causes a reduction in plant height and crop yield, and rice is prone to lodging in the late growth stage because of panicle initiation. We used two water irrigation modes and four fertilizer application intervals to investigate the relationship between lodging and various cultivation conditions over 2 years. RESULTS: Plant height data were collected and combined with aerial images, revealing that rice lodging was closely related to the nitrogen fertilizer content. The aerial images demonstrated that lodging mainly occurred in the fields treated with a high-nitrogen fertilizer, and analysis of variance revealed that plant height was signifi-cantly affected by nitrogen fertilizer. These results demonstrated that rice plant height in the booting stage was significantly positively correlated with the lodging results (r = 0.67) and nega-tively correlated with yield (r = - 0.46). If the rice plant height in the booting stage exceeded 70.7 cm and nitrogen fertilizer was continuously applied, according to the predicted growing curve of plant height, the plant would be at risk of lodging. Results showed more rainfall accumulated in the later stage of rice growth accompanied by strong instantaneous gusts, the risk of lodging in-creased. CONCLUSION: The results provide predictions that can be applied in intelligent production and lodging risk management, and they form the basis of cultivation management and response policies for each growth period.

NADPH Oxidase RbohD and Ethylene Signaling are Involved in Modulating Seedling Growth and Survival Under Submergence Stress.

In higher plants under low oxygen or hypoxic conditions, the phytohormone ethylene and hydrogen peroxide (H2O2) are involved in complex regulatory mechanisms in hypoxia signaling pathways. The respiratory burst oxidase homolog D (RbohD), an NADPH oxidase, is involved in the primary stages of hypoxia signaling, modulating the expression of downstream hypoxia-inducible genes under hypoxic stress. In this study, our data revealed that under normoxic conditions, seed germination was delayed in the rbohD/ein2-5 double mutant, whereas postgermination stage root growth was promoted. Under submergence, the rbohD/ein2-5 double mutant line had an inhibited root growth phenotype. Furthermore, chlorophyll content and leaf survival were reduced in the rbohD/ein2-5 double mutant compared with wild-type plants under submerged conditions. In quantitative RT-PCR analysis, the induction of Ethylene-responsive factor 73/hypoxia responsive 1 (AtERF73/HRE1) and alcohol dehydrogenase 1 (AtADH1) transcripts was lower in the rbohD/ein2-5 double mutant during hypoxic stress than in wild-type plants and in rbohD and ein2-5 mutant lines. Taken together, our results indicate that an interplay of ethylene and RbohD is involved in regulating seed germination and post-germination stages under normoxic conditions. Moreover, ethylene and RbohD are involved in modulating seedling root growth, leaf chlorophyll content, and hypoxia-inducible gene expression under hypoxic conditions.

The Seedlings of Different Japonica Rice Varieties Exhibit Differ Physiological Properties to Modulate Plant Survival Rates under Submergence Stress.

Oryza sativa is a major food crop in Asia. In recent years, typhoons and sudden downpours have caused field flooding, which has resulted in serious harm to the production of rice. In this study, our data revealed that the plant heights of the five Japonica varieties increased during submergence. The elongation rates of TN14, KH139, and TK9 increased significantly during submergence. Chlorophyll contents of the five varieties significantly decreased after submergence and increased after recovery. Moreover, the chlorophyll content of KH139 was significantly higher than those of the other four varieties after recovery. The plant survival rates of the five varieties were higher than 50% after four-day submergence. After eight-day submergence, the survival rate of KH139 remained at 90%, which was the highest among the different varieties. The KH139 presented lower accumulation of hydrogen peroxide and the catalase activity than those of the other four varieties under submergence. The sucrose synthase 1 and alcohol dehydrogenase 1 were induced in KH139 under submergence. The results presented that different varieties of japonica rice have different flood tolerances, especially KH139 under submergence was superior to that of the other four varieties. These results can provide crucial information for future research on japonica rice under flooding stress.

Ethylene-mediated signaling confers thermotolerance and regulates transcript levels of heat shock factors in rice seedlings under heat stress.

BACKGROUND: Agriculture is highly dependent on climate. Increases in temperature caused by global warming pose challenges for crop production. Heat stress induces oxidative damage to cell membranes and then causes cell death. Plants have developed various responses to elevated temperatures, including hormone signaling pathways and heat shock factors that elevate their thermotolerance. In response to heat stress, the gaseous hormone ethylene is produced through regulation of the expression of signaling-related genes to modulate resource allocation dynamics. For comprehensive understanding of the role of ethylene, this study used an ethylene precursor to analyze the ethylene signaling pathway involved in adjustment of the homeostasis of the antioxidant system and to evaluate heat shock factor expression in rice seedlings under heat stress. RESULTS: Levels of cell membrane oxidation and ion leakage were reduced in rice seedlings under heat treatment combined with ethylene precursor treatment, conferring enhanced thermotolerance. Reduction of the fresh weight and chlorophyll a/b ratio in rice seedlings was lower in rice seedlings under heat stress with ethylene precursor treatment than in those under heat stress only. Moreover, reduction of antioxidant response caused by heat stress was ameliorated by treatment with ethylene precursors such as catalase and total peroxidase. Quantitative reverse transcriptase-polymerase chain reaction showed higher expression levels of heat shock factors such as HSFA1a and HSFA2a, c, d, e, and f and ethylene-signaling-related genes such as ethylene insensitive 2, ethylene insensitive-like 1, and ethylene insensitive-like 2 in rice seedlings under heat stress with ethylene precursor treatment than in rice seedlings under heat stress only. CONCLUSION: Ethylene-mediated signaling was involved in the reduction of oxidative damage, maintenance of chlorophyll content, and enhancement of thermotolerance in rice seedlings under heat stress. Furthermore, this study revealed heat shock factors and ethylene-signaling-related genes involved in complex network regulation that confers thermotolerance to rice seedlings.

Ethylene signaling involves in seeds germination upon submergence and antioxidant response elicited confers submergence tolerance to rice seedlings.

BACKGROUND: Flooding has negative impact on agriculture. The plant hormone ethylene is involved in plant growth and stress responses, which are important role in tolerance and adaptation regulatory mechanisms during submergence stress. Ethylene signaling crosstalk with gibberellin signaling enhances tolerance in lowland rice (Flood Resistant 13A) through a quiescence strategy or in deepwater rice through an escape strategy when rice is submerged. Information regarding ethylene-mediated priming in submergence stress tolerance in rice is scant. Here, we used 1-aminocyclopropane-1-carboxylic acid, an ethylene precursor, to evaluate the response in submerged rice seedlings. RESULTS: The germination rate and mean germination times of rice seeds was higher in seedlings under submergence only when ethylene signaling was inhibited by supplemented with silver nitrate (AgNO3). Reduced leaf chlorophyll contents and induced senescence-associated genes in rice seedlings under submergence were relieved by pretreatment with an ethylene precursor. The ethylene-mediated priming by pretreatment with an ethylene precursor enhanced the survival rate and hydrogen peroxide (H2O2) and superoxide (O2-) anion accumulation and affected antioxidant response in rice seedlings. CONCLUSIONS: Pretreatment with an ethylene precursor leads to reactive oxygen species generation, which in turn triggered the antioxidant response system, thus improving the tolerance of rice seedlings to complete submergence stress. Thus, H2O2 signaling may contribute to ethylene-mediated priming to submergence stress tolerance in rice seedlings.

Ethylene signaling modulates contents of catechin and ability of antioxidant in Camellia sinensis.

BACKGROUND: Tea is one of the most popular beverages in the world. There are many secondary metabolites can be found in tea such as anthocyanins, proanthocyanidins, flavonols and catechins. These secondary metabolites in plants are proved to act protective components for human health effect. Plant hormone ethylene is considered to have an important role in regulation of plant development and signal transduction. This study evaluated the effect of ethylene signaling regulation in phenolic compounds in tea plants. The ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) enhanced contents of total catechin in treated oolong tea seedlings. RESULTS: The degree of epigallocatechin and epicatechin galloylation was increased after ACC treatment in oolong tea seedlings by high performance liquid chromatography determination. The contents of anthocyanins, flavonoids, and total polyphenol were higher after ACC treatment in comparison with control. Antioxidant enzyme such as catalase, superoxide dismutase, and total peroxidase decreased their antioxidant activities after ACC treatment, yet the activity of ascorbate peroxidase is increased. The ability of oxygen radical absorption and 2,2-diphenyl-1-picrylhydrazyl was used to evaluate the antioxidant activity, which was enhanced by ACC treatment. CONCLUSIONS: Taken together the results of this study demonstrate that the ethylene signaling is involved in modulation of secondary metabolites accumulation and antioxidant ability that to enhance the benefit of human health in tea products.

Rothia dentocariosa bacteremia in children: report of two cases and review of the literature.

Rothia dentocariosa, a pleomorphic, fastidious, Gram-positive rod, is a normal inhabitant of the oropharynx. It is a well-known causative agent of dental plaques and periodontal disease. Generally regarded as of low virulence to humans, R. dentocariosa has been increasingly recognized as a pathogen in adults and often associated with infective endocarditis. It should not necessarily be regarded as a contaminant when the isolate comes from areas other than the oropharynx, especially from the blood. We report two cases of R. dentocariosa bacteremia, including an 8-month-old boy with repaired transposition of the great arteries, and a healthy 20-month-old girl with herpangina.

ERF73/HRE1 is involved in H2O2 production via hypoxia-inducible Rboh gene expression in hypoxia signaling.

Hypoxia deprives cells of energy and induces severe physical damage in embryophytes. Under hypoxia, the equilibrium between ethylene and H2O2 affects the response of the transcription factor AtERF73/HRE1. To evaluate the role of AtERF73/HRE1 during hypoxia signaling, we used three independent AtERF73/HRE1 knockout lines to detect H2O2 accumulation. The results revealed that under hypoxia, H2O2 accumulation in the AtERF73/HRE1 knockout lines decreased, indicating that AtERF73/HRE1 uses a negative feedback regulation mechanism to influence the production of H2O2 induced through hypoxia signal transduction. Quantitative RT-PCR analyses showed that oxygen deficiency had different effects on the expression of the hypoxia-induced genes Rboh B, D, G, and I in the AtERF73/HRE1 knockout lines. In particular, Rboh B and D expression were increased, whereas Rboh G expression was decreased. The expression of Rboh I was increased at 1 h but decreased at 3 h during hypoxia treatment in the AtERF73/HRE1 knockout lines. Similarly, the transcript levels of antioxidant and hypoxia-induced/ethylene response genes in the AtERF73/HRE1 knockout lines were affected by hypoxic stress, indicating that AtERF73/HRE1 is essential to hypoxia signal transduction in embryophytes. Additionally, in histochemical analysis, AtERF73/HRE1 promoter-induced GUS expression was detected in various plant parts throughout the plant growth process (e.g., leaves, inflorescences, siliques), particularly in the edges of mature leaves and guard cells. Taken together, our results confirm that AtERF73/HRE1 plays a role in H2O2 production by affecting the hypoxia-induced expression of Rboh genes in hypoxia signal transduction.

Physiological and molecular responses of seedlings of an upland rice ('Tung Lu 3') to total submergence compared to those of a submergence-tolerant lowland rice ('FR13A').

BACKGROUND: Understanding the responses of rice to environmental stresses such as unscheduled submergence is of pressing important owing to increasing severity of weather thought to arise from global climate change. When rice is completely submerged, different types adopt either a quiescence survival strategy (i.e., minimal shoot elongation) or an escape strategy (i.e., enhanced shoot elongation). Each strategy can prolong survival depending on the circumstances. While submergence responses have been studied in rice typical of lowland and flood-prone areas, few studies have explored the physiological and molecular properties of upland rice under submergence. Here, we use seedlings of the upland rice 'Tung Lu 3' ('TL3') to analyze physiological and molecular responses to submergence. We compare them with those of 'FR13A', a lowland rice that tolerates submergence by adopting the quiescence strategy. RESULTS: Plant height and distance between leaf sheaths, increased rapidly in 'TL3' under submergence. Although this indicated a strong escape strategy the seedlings remained totally underwater for the duration of the experiments. In contrast, 'FR13A' elongated much less. Consequently, after 4 days complete submergence followed by drainage, 'TL3' lodged much more severely than 'FR13A'. After 10 d complete submergence, 55% of 'TL3' seedlings survived compared to 100% in 'FR13A'. Chlorophyll a, b and total chlorophyll concentrations of the 2nd oldest leaves of 'TL3' were also significantly above those of 'FR13A' (but were lower than 'FR13A' in the 3rd oldest leaves) and less hydrogen peroxide accumulated in 'TL3'. Peroxidase activity in submerged 'TL3' was also greater than in 'FR13A' 1 day after submergence. Quantitative RT-PCR showed increased expression of sucrose synthase 1 and alcohol dehydrogenases 1 after 2 days complete submergence with significantly higher levels in 'TL3' compared to 'FR13A'. Expression was also higher in 'TL3' under non-submerged conditions. CONCLUSIONS: The upland rice line 'TL3' gave a stronger elongation response than 'FR13A' to complete submergence. This escape strategy is widely considered to prejudice survival when the plant remains totally submerged. However, contrary to expectations, 'TL3' survival rates were substantial although below those for 'FR13A' while physiological, biochemical and molecular parameters linked to adaptation differed in detail but appeared to be broadly comparable. These findings highlight that submergence tolerance is determine not only by the adoption of quiescence or escape strategies but maybe by metabolic and physiological properties unrelated to the underwater elongation rate.