Glycinebetaine mitigates tomato chilling stress by maintaining high-cyclic electron flow rate of photosystem I and stability of photosystem II.

KEY MESSAGE: Glycinebetaine alleviates chilling stress by protecting photosystems I and II in BADH-transgenic and GB-treated tomato plants, which can be an effective strategy for improving crop chilling tolerance. Tomato (Solanum lycopersicum) is one of the most cultivated vegetables in the world, but is highly susceptible to chilling stress and does not naturally accumulate glycinebetaine (GB), one of the most effective stress protectants. The protective mechanisms of GB on photosystem I (PSI) and photosystem II (PSII) against chilling stress, however, remain poorly understood. Here, we address this problem through exogenous GB application and generation of transgenic tomatoes (Moneymaker) with a gene encoding betaine aldehyde dehydrogenase (BADH), which is the key enzyme in the synthesis of GB, from spinach. Our results demonstrated that GB can protect chloroplast ultramicrostructure, alleviate PSII photoinhibition and maintain PSII stability under chilling stress. More importantly, GB increased the electron transfer between QA and QB and the redox potential of QB and maintained a high rate of cyclic electron flow around PSI, contributing to reduced production of reactive oxygen species, thereby mitigating PSI photodamage under chilling stress. Our results highlight the novel roles of GB in enhancing chilling tolerance via the protection of PSI and PSII in BADH transgenic and GB-treated tomato plants under chilling stress. Thus, introducing GB-biosynthetic pathway into tomato and exogenous GB application are effective strategies for improving chilling tolerance.

Glycinebetaine mitigated the photoinhibition of photosystem II at high temperature in transgenic tomato plants.

Photosystem II (PSII), especially the D1 protein, is highly sensitive to the detrimental impact of heat stress. Photoinhibition always occurs when the rate of photodamage exceeds the rate of D1 protein repair. Here, genetically engineered codA-tomato with the capability to accumulate glycinebetaine (GB) was established. After photoinhibition treatment at high temperature, the transgenic lines displayed more thermotolerance to heat-induced photoinhibition than the control line. GB maintained high expression of LeFtsHs and LeDegs and degraded the damaged D1 protein in time. Meanwhile, the increased transcription of synthesis-related genes accelerated the de novo synthesis of D1 protein. Low ROS accumulation reduced the inhibition of D1 protein translation in the transgenic plants, thereby reducing protein damage. The increased D1 protein content and decreased phosphorylated D1 protein (pD1) in the transgenic plants compared with control plants imply that GB may minimize photodamage and maximize D1 protein stability. As D1 protein exhibits a high turnover, PSII maybe repaired rapidly and efficiently in transgenic plants under photoinhibition treatment at high temperature, with the resultant mitigation of photoinhibition of PSII.

Comparative effects of glycinebetaine on the thermotolerance in codA- and BADH-transgenic tomato plants under high temperature stress.

KEY MESSAGE: We propose that codA tomato plants exhibited higher degrees of enhanced thermotolerance than BADH tomato plants, and H2O2 as a signaling molecule also plays an important role in heat resistance. Betaine aldehyde dehydrogenase (BADH) and choline oxidase (COD) are key enzymes in glycinebetaine (GB) synthesis. In this study, two kinds of transgenic tomato plants, which were transformed with BADH gene and codA gene, respectively, were used to explore their thermotolerance. Our results showed that the levels of GB in leaves of the fourteen independent transgenic lines ranged from 1.9 µmol g-1 fresh weight to 3.4 µmol g-1 fresh weight, while GB was almost undetectable in leaves of WT plants. CO2 assimilation and photosystem II (PSII) photochemical activity in transgenic plants were more thermotolerant than WT plants, especially the codA-transgenic plants showed the most. Significant accumulation of hydrogen peroxide (H2O2), superoxide anion radical (O2·-), and malondialdehyde (MDA) were more in WT plants than transgenic plants, while this accumulation in codA-transgenic plant was the least. Furthermore, the expression of the heat response genes and the accumulation of heat shock protein 70 (HSP70) were found to be more in transgenic plants than that in WT plants during heat stress, as well as showing the most expression and accumulation of HSP70 in the codA-transgenic plants. Taken together, our results suggest that the enhanced thermotolerance in transgenic plants is due to the positive role of GB in response to heat stress. And interestingly, in addition to the major role of GB in codA-transgenic plants, H2O2 as a signaling molecule may also play an important role in heat resistance, leading to higher thermotolerance compared to BADH-transgenic plants.

Hv-CBF2A overexpression in barley accelerates COR gene transcript accumulation and acquisition of freezing tolerance during cold acclimation.

C-Repeat Binding Factors (CBFs) are DNA-binding transcriptional activators of gene pathways imparting freezing tolerance. Poaceae contain three CBF subfamilies, two of which, HvCBF3/CBFIII and HvCBF4/CBFIV, are unique to this taxon. To gain mechanistic insight into HvCBF4/CBFIV CBFs we overexpressed Hv-CBF2A in spring barley (Hordeum vulgare) cultivar 'Golden Promise'. The Hv-CBF2A overexpressing lines exhibited stunted growth, poor yield, and greater freezing tolerance compared to non-transformed 'Golden Promise'. Differences in freezing tolerance were apparent only upon cold acclimation. During cold acclimation freezing tolerance of the Hv-CBF2A overexpressing lines increased more rapidly than that of 'Golden Promise' and paralleled the freezing tolerance of the winter hardy barley 'Dicktoo'. Transcript levels of candidate CBF target genes, COR14B and DHN5 were increased in the overexpressor lines at warm temperatures, and at cold temperatures they accumulated to much higher levels in the Hv-CBF2A overexpressors than in 'Golden Promise'. Hv-CBF2A overexpression also increased transcript levels of other CBF genes at FROST RESISTANCE-H2-H2 (FR-H2) possessing CRT/DRE sites in their upstream regions, the most notable of which was CBF12. CBF12 transcript levels exhibited a relatively constant incremental increase above levels in 'Golden Promise' both at warm and cold. These data indicate that Hv-CBF2A activates target genes at warm temperatures and that transcript accumulation for some of these targets is greatly enhanced by cold temperatures.

Alteration of flower color in Iris germanica L. 'Fire Bride' through ectopic expression of phytoene synthase gene (crtB) from Pantoea agglomerans.

KEY MESSAGE: Genetic modulation of the carotenogenesis in I. germanica 'Fire Bride' by ectopic expression of a crtB gene causes several flower parts to develop novel orange and pink colors. Flower color in tall bearded irises (Iris germanica L.) is determined by two distinct biochemical pathways; the carotenoid pathway, which imparts yellow, orange and pink hues and the anthocyanin pathway, which produces blue, violet and maroon flowers. Red-flowered I. germanica do not exist in nature and conventional breeding methods have thus far failed to produce them. With a goal of developing iris cultivars with red flowers, we transformed a pink iris I. germanica, 'Fire Bride', with a bacterial phytoene synthase gene (crtB) from Pantoea agglomerans under the control of the promoter region of a gene for capsanthin-capsorubin synthase from Lilium lancifolium (Llccs). This approach aimed to increase the flux of metabolites into the carotenoid biosynthetic pathway and lead to elevated levels of lycopene and darker pink or red flowers. Iris callus tissue ectopically expressing the crtB gene exhibited a color change from yellow to pink-orange and red, due to accumulation of lycopene. Transgenic iris plants, regenerated from the crtB-transgenic calli, showed prominent color changes in the ovaries (green to orange), flower stalk (green to orange), and anthers (white to pink), while the standards and falls showed no significant differences in color when compared to control plants. HPLC and UHPLC analysis confirmed that the color changes were primarily due to the accumulation of lycopene. In this study, we showed that ectopic expression of a crtB can be used to successfully alter the color of certain flower parts in I. germanica 'Fire Bride' and produce new flower traits.

A plea for more careful scholarship in reviewing evidence: the case of mammographic screening.

Objectives: To identify issues of principle and practice giving rise to misunderstandings in reviewing evidence, to illustrate these by reference to the Nordic Cochrane Review (NCR) and its interpretation of two trials of mammographic screening, and to draw lessons for future reviewing of published results. Methods: A narrative review of the publications of the Nordic Cochrane Review of mammographic screening (NCR), the Swedish Two-County Trial (S2C) and the Canadian National Breast Screening Study 1 and 2 (CNBSS-1 and CNBSS-2). Results: The NCR concluded that the S2C was unreliable, despite the review's complaints being shown to be mistaken, by direct reference to the original primary publications of the S2C. Repeated concerns were expressed by others about potential subversion of randomisation in CNBSS-1 and CNBSS-2; however, the NCR continued to rely heavily on the results of these trials. Since 2022, however, eyewitness evidence of such subversion has been in the public domain. Conclusions: An over-reliance on nominal satisfaction of checklists of criteria in systematic reviewing can lead to erroneous conclusions. This occurred in the case of the NCR, which concluded that mammographic screening was ineffective or minimally effective. Broader and more even-handed reviews of the evidence show that screening confers a substantial reduction in breast cancer mortality. Advances in knowledge: Those carrying out systematic reviews should be aware of the dangers of over-reliance on checklists and guidelines. Readers of systematic reviews should be aware that a systematic review is just another study, with the capability that all studies have of coming to incorrect conclusions. When a review seems to overturn the current position, it is essential to revisit the publications of the primary research.

Cloning and functional characterization of a gene for capsanthin-capsorubin synthase from tiger lily (Lilium lancifolium Thunb. 'Splendens').

The orange color of tiger lily (Lolium lancifolium 'Splendens') flowers is due, primarily, to the accumulation of two κ-xanthophylls, capsanthin and capsorubin. An enzyme, known as capsanthin-capsorubin synthase (CCS), catalyzes the conversion of antheraxanthin and violaxanthin into capsanthin and capsorubin, respectively. We cloned the gene for capsanthin-capsorubin synthase (Llccs) from flower tepals of L. lancifolium by the rapid amplification of cDNA ends (RACE) with a heterologous non-degenerate primer that was based on the sequence of a gene for lycopene ß-cyclase (lcyB). The full-length cDNA of Llccs was 1,785 bp long and contained an open reading frame of 1,425 bp that encoded a polypeptide of 474 amino acids with a predicted N-terminal plastid-targeting sequence. Analysis by reverse transcription-PCR (RT-PCR) revealed that expression of Llccs was spatially and temporally regulated, with expression in flower buds and flowers of L. lancifolium but not in vegetative tissues. Stable overexpression of the Llccs gene in callus tissue of Iris germanica, which accumulates several xanthophylls including violaxanthin, the precursor of capsorubin, resulted in transgenic callus whose color had changed from its normal yellow to red-orange. This novel red-orange coloration was due to the accumulation of two non-native κ-xanthophylls, capsanthin and capsorubin, as confirmed by HPLC and ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) analysis with authentic standards. Cloning of the Llccs gene should advance our understanding of the molecular and genetic mechanisms of the biosynthesis of κ-carotenoids in general and in the genus Lilium in particular, and will facilitate transgenic alterations of the colors of flowers and fruits of many plant species.

Quantifying the duration of the preclinical detectable phase in cancer screening: a systematic review.

OBJECTIVES: The aim of this study was to provide an overview of published mathematical estimation approaches to quantify the duration of the preclinical detectable phase (PCDP) using data from cancer screening programs. METHODS: A systematic search of PubMed and Embase was conducted for original studies presenting mathematical approaches using screening data. The studies were categorized by mathematical approach, data source, and assumptions made. Furthermore, estimates of the duration of the PCDP of breast and colorectal cancer were reported per study population. RESULTS: From 689 publications, 34 estimation methods were included. Five distinct types of mathematical estimation approaches were identified: prevalence-to-incidence ratio (n=8), maximum likelihood estimation (n=16), expectation-maximization algorithm (n=1), regression of observed on expected (n=6) and Bayesian Markov-chain Monte Carlo estimation (n=5). Fourteen studies used data from both screened and unscreened populations, whereas 19 studies included only information from a screened population. Estimates of the duration of the PCDP varied between 2 years and 7 years for breast cancer in the Health Insurance Plan study (annual mammography and clinical breast examinations in women aged 40-64 years) and 2 years and 5 years for colorectal cancer in the Calvados study (a guaiac fecal occult blood test in men and women aged 45-74 years). CONCLUSIONS: Different types of mathematical approaches lead to different estimates of the PCDP duration. We advise researchers to use the method that matches the data available, and to use multiple methods for estimation when possible, since no method is perfect.

Glycinebetaine protects plants against abiotic stress: mechanisms and biotechnological applications.

Various compatible solutes enable plants to tolerate abiotic stress, and glycinebetaine (GB) is one of the most-studied among such solutes. Early research on GB focused on the maintenance of cellular osmotic potential in plant cells. Subsequent genetically engineered synthesis of GB-biosynthetic enzymes and studies of transgenic plants demonstrated that accumulation of GB increases tolerance of plants to various abiotic stresses at all stages of their life cycle. Such GB-accumulating plants exhibit various advantageous traits, such as enlarged fruits and flowers and/or increased seed number under non-stress conditions. However, levels of GB in transgenic GB-accumulating plants are relatively low being, generally, in the millimolar range. Nonetheless, these low levels of GB confer considerable tolerance to various stresses, without necessarily contributing significantly to cellular osmotic potential. Moreover, low levels of GB, applied exogenously or generated by transgenes for GB biosynthesis, can induce the expression of certain stress-responsive genes, including those for enzymes that scavenge reactive oxygen species. Thus, transgenic approaches that increase tolerance to abiotic stress have enhanced our understanding of mechanisms that protect plants against such stress.

Glycinebetaine enhances the tolerance of tomato plants to high temperature during germination of seeds and growth of seedlings.

Tomato (Lycopersicon esculentum cv. 'Moneymaker') was transformed with a codA gene, from Arthrobacter globiformis, for choline oxidase that had been modified to allow targeting to both chloroplasts and the cytosol. Glycinebetaine (GB) accumulated in seeds of transformed plants up to 1 µmol g(-1) dry weight (DW), while no detectable GB was found in wild-type (WT) seeds. The codA-transgenic seeds germinated faster and at higher frequency than WT seeds with high temperature treatment. After heat stress, levels of expression of a mitochondrial small heat-shock protein (MT-sHSP), heat-shock protein 70 (HSP70) and heat-shock cognate 70 (HSC70) were higher in transgenic seeds than in WT seeds during heat stress, and the accumulation of HSP70 was more prominent in codA-transgenic seeds than in WT seeds. Addition of GB to the germination medium or imbibition of seeds in a solution of GB enhanced the tolerance of WT seeds to high temperatures. WT seeds treated with exogenous GB also expressed heat-shock genes at elevated levels and accumulated more HSP70 than controls. Our results suggest that GB, either applied exogenously or accumulated in vivo in codA-transgenic seeds, enhanced the expression of heat-shock genes in and improved the tolerance to high temperature of tomato seeds during germination.

A comparison of the low temperature transcriptomes and CBF regulons of three plant species that differ in freezing tolerance: Solanum commersonii, Solanum tuberosum, and Arabidopsis thaliana.

Solanum commersonii and Solanum tuberosum are closely related plant species that differ in their abilities to cold acclimate; whereas S. commersonii increases in freezing tolerance in response to low temperature, S. tuberosum does not. In Arabidopsis thaliana, cold-regulated genes have been shown to contribute to freezing tolerance, including those that comprise the CBF regulon, genes that are controlled by the CBF transcription factors. The low temperature transcriptomes and CBF regulons of S. commersonii and S. tuberosum were therefore compared to determine whether there might be differences that contribute to their differences in ability to cold acclimate. The results indicated that both plants alter gene expression in response to low temperature to similar degrees with similar kinetics and that both plants have CBF regulons composed of hundreds of genes. However, there were considerable differences in the sets of genes that comprised the low temperature transcriptomes and CBF regulons of the two species. Thus differences in cold regulatory programmes may contribute to the differences in freezing tolerance of these two species. However, 53 groups of putative orthologous genes that are cold-regulated in S. commersonii, S. tuberosum, and A. thaliana were identified. Given that the evolutionary distance between the two Solanum species and A. thaliana is 112-156 million years, it seems likely that these conserved cold-regulated genes-many of which encode transcription factors and proteins of unknown function-have fundamental roles in plant growth and development at low temperature.

Mortality and suicide after self-harm: community cohort study in Taiwan.

BACKGROUND: Little is known about outcomes after self-harm in East Asia. AIMS: To investigate mortality after self-harm in a Taiwanese population. METHOD: Between 2000 and 2003, 1083 individuals who self-harmed were identified through a population self-harm register in Nantou County, Taiwan, and followed until 2007 for date and cause of death on a national mortality database. RESULTS: In total, 145 individuals died, 48 through suicide. The risks of all-cause and suicide mortality in the first year were 4.7% and 2.1% respectively, representing 8- and 131-fold age- and gender-standardised increases. Male gender and older age were independent risk factors for both suicide and non-suicide mortality. Use of more lethal methods in the index episode was associated with higher mortality but this was accounted for by gender. CONCLUSIONS: Results in this sample support the recommendation that people with a history of recent self-harm should be a major target for suicide prevention programmes.

Glycinebetaine: an effective protectant against abiotic stress in plants.

Glycinebetaine (GB) has been studied extensively as a compatible solute because of the availability of GB-accumulating transgenic plants that harbor a variety of transgenes for GB-biosynthetic enzymes. Both the exogenous application of GB and the genetically engineered biosynthesis of GB increase the tolerance of plants to abiotic stress. As reviewed here, studies of such increased tolerance to abiotic stress have led to considerable progress in the characterization of the roles of GB in stress tolerance in plants. In particular, the reproductive organs of GB-accumulating transgenic plants exhibit enhanced tolerance to abiotic stress. Furthermore, accumulation of GB results in increased yield potentials under non-stress conditions.

A community-based study of case fatality proportion among those who carry out suicide acts.

OBJECTIVE: To investigate the case fatality proportion and associated factors in those carrying out suicide acts in Nantou, Taiwan. METHOD: Data from 1,171 suicide acts (including 973 with deliberate self harm and 198 completed suicides), identified between July 2000 and February 2003, were collected from a population suicide register in Nantou County, Taiwan. Case fatality proportion and the independent effects of demographic factors and suicide method on case fatality were investigated. RESULTS: The overall case fatality proportion was 16.9%, with higher proportions in men (26.3%) and in those aged 65 and over (37.9%). Hanging was the most lethal method (fatality proportion = 81.5%); pesticide was both commonly used and associated with a high case fatality (fatality proportion = 26.3%). Only age (increased with age) and suicide method were found to be independently associated with the risk of fatality. CONCLUSIONS: Suicide method and older age are independent predictors of the fatality of suicide acts. Suicide prevention strategy and clinical assessment ought to take into account of these two factors. Diminution of pesticide toxicity and control of access to pesticides are important considerations for suicide prevention in rural Taiwan.

Genetic engineering of the biosynthesis of glycinebetaine enhances the fruit development and size of tomato.

Glycinebetaine has been widely considered as an effective protectant against abiotic stress in plants, and also found to promote plant growth under normal growing conditions, especially during the reproductive stage. Betaine aldehyde dehydrogenase (BADH) and choline oxidase (COD) are two key enzymes which have been used to confer glycinebetaine synthesis in plant which normally does not synthesis glycinebetaine. In this study, we used the tomato (Solanum lycopersicum, cv 'Moneymaker') plants of wild-type and the transgenic lines codA (L1, L2) and BADH (2, 46), which were transformed with codA and BADH, respectively, to study the impact of glycinebetaine on tomato fruit development. Our results showed that the codA and BADH transgenes induced the formation of enlarged flowers and fruits in transgenic tomato plants. In addition, the transgenic tomato plants had a higher photosynthetic rate, higher assimilates content, and higher leaf chlorophyll content than the wild-type plants. We also found that the enlargement of fruit size was related to the contents of phytohormones, such as auxin, brassinolide, gibberellin, and cytokinin. Additionally, qPCR results indicated that the expressions levels of certain genes related to fruit growth and development were also elevated in transgenic plants. Finally, transcriptome sequencing results revealed that the differences in the levels of gene expression in tomato fruit between the transgenic and wild-type plants were observed in multiple pathways, predominantly those of photosynthesis, DNA replication, plant hormone signal transduction, and biosynthesis. Taken together, our results suggest that glycinebetaine promotes tomato fruit development via multiple pathways. We propose that genetic engineering of glycinebetaine synthesis offers a novel approach to enhance the productivity of tomato and other crop plants.

Elevation of C-reactive protein level is associated with synchronous and advanced colorectal neoplasm in men.

OBJECTIVES: Chronic inflammation has been implicated in the development of colorectal cancer (CRC). The presence of low-grade systemic inflammation, as determined by an elevation of high-sensitivity C-reactive protein (CRP), has been associated with an increased risk of cardiovascular diseases and cancers. However, previous studies of CRP and CRC in cohorts that comprised different genders have yielded conflicting results and little is known about CRP levels in individuals with colorectal adenomas, the precursor lesion of CRC. This study aims to elucidate the association of CRP and colorectal neoplasia. METHODS: Plasma CRP levels were examined using a cross-sectional design in 6,695 consecutive ethnic Chinese adults who had undergone a complete colonoscopy following a thorough routine health evaluation. Logistic regression analysis was used to correlate the risk of colorectal neoplasia with CRP levels. RESULTS: Plasma CRP levels were significantly higher in subjects with colorectal neoplasia than in those without neoplasia (1.85 mg/L vs 1.55 mg/L, P= 0.04). The presence of synchronous neoplasia, advanced neoplasia, and concurrent synchronous and advanced neoplasia were associated with elevated levels of plasma CRP, after adjustment for other risk factors. Gender stratification revealed a positive association between elevated CRP levels and the risk of colorectal neoplasia in men, but no such corresponding association existed in women. CONCLUSIONS: Elevated plasma CRP levels are independently associated with an increased risk of colorectal neoplasia in men, but not in women. These data support the association between chronic inflammation and colorectal neoplasia in men and provide new insights into the underlying mechanisms that warrant further investigation.

Ectopic AtCBF1 over-expression enhances freezing tolerance and induces cold acclimation-associated physiological modifications in potato.

We studied the effect of ectopic AtCBF over-expression on physiological alterations that occur during cold exposure in frost-sensitive Solanum tuberosum and frost-tolerant Solanum commersonii. Relative to wild-type plants, ectopic AtCBF1 over-expression induced expression of COR genes without a cold stimulus in both species, and imparted a significant freezing tolerance gain in both species: 2 degrees C in S. tuberosum and up to 4 degrees C in S. commersonii. Transgenic S. commersonii displayed improved cold acclimation potential, whereas transgenic S. tuberosum was still incapable of cold acclimation. During cold treatment, leaves of wild-type S. commersonii showed significant thickening resulting from palisade cell lengthening and intercellular space enlargement, whereas those of S. tuberosum did not. Ectopic AtCBF1 activity induced these same leaf alterations in the absence of cold in both species. In transgenic S. commersonii, AtCBF1 activity also mimicked cold treatment by increasing proline and total sugar contents in the absence of cold. Relative to wild type, transgenic S. commersonii leaves were darker green, had higher chlorophyll and lower anthocyanin levels, greater stomatal numbers, and displayed greater photosynthetic capacity, suggesting higher productivity potential. These results suggest an endogenous CBFpathway is involved in many of the structural, biochemical and physiological alterations associated with cold acclimation in these Solanum species.

Ectopic expression of StCBF1and ScCBF1 have different functions in response to freezing and drought stresses in Arabidopsis.

Solanum tuberosum potato species constitute the bulk of economically and agronomically important potato production. However, S. tuberosum is a drought- and frost-sensitive species that is incapable of acclimating to the cold. Solanum commersonii is a tuber-bearing wild potato species that exhibits greater frost and drought resistance than S. tuberosum. CBF/DREB (C-REPET BINDING FACTOR/DROUGHT RESPONSE ELEMENT BINGING FACTOR) transcription factors play important roles in response to a variety of abiotic stresses, such as cold, drought and salt stresses. To explore different functions between S. tuberosum CBF1 (StCBF1) and S. commersonii CBF1 (ScCBF1), Arabidopsis was transformed with the ScCBF1 and StCBF1 genes driven by a constitutive CaMV35S promoter. Our results reveal that the ScCBF1 transgenic lines are much more tolerant to freezing and drought than the StCBF1 transgenic lines. The development of transgenic plants was altered, resulting in dwarf phenotype with delayed flowering and thicker and additional rosette leaves. The expression levels of several COR (COLD-RESPONSIVE) genes and development-related genes, including genes that inhibited plant growth (GA2ox7, RGL3) and delayed flowering (FLC) were higher in transgenic plants. These results suggest that these two potato CBF1 play important roles in the plant response to abiotic stress and can influence plant growth and development, and ScCBF1 plays a more pronounced function than StCBF1.

Genetic Engineering of the Biosynthesis of Glycine Betaine Modulates Phosphate Homeostasis by Regulating Phosphate Acquisition in Tomato.

Glycine betaine (GB), as a putative compatible substance, protects plants against the damaging effects of abiotic stresses. Phosphorus deficiency is one type of abiotic stress that is detrimental to plant growth. Maintenance of phosphate (Pi) homeostasis is crucial. This study demonstrates GB-regulated phosphate homeostasis in the tomato (Solanum lycopersicum cv. 'Moneymaker') transformed with the choline oxidase gene codA from Arthrobacter globiformis. The codA-transgenic lines displayed more resistance to low-phosphate stress. The data revealed that the wild-type plants were stunted and consistently retained less Pi than transgenic lines, especially when grown under low-phosphate conditions. This difference in Pi retention was attributable to the enhanced Pi uptake ability in the transgenic lines. The transgenic plants translocated more Pi into the plant cell due to the enhanced enzymatic activity of plasma membrane H+-ATPase and increased Pi/H+ co-transport, which improved Pi uptake. The differential expression of 'PHO regulon' genes further maintained intracellular Pi homeostasis. Furthermore, GB maintained a higher photosynthesis rate, thus increasing the production and translocation of sucrose via phloem loading to enhance plant response to low-phosphate stress. We conclude that GB mediates Pi uptake and translocation by regulating physiological and biochemical processes that promote adaptation to environmental changes in Pi availability. These processes eventually lead to better growth and development of the codA-transgenic lines. This finding will help to further elucidate the signaling mechanism of how GB perceives and transmits low-phosphate signals to alleviate Pi nutritional stress.