Yong-sic Hwang

Comparative analyses of lipidomes and transcriptomes reveal a concerted action of multiple defensive systems against photooxidative stress in Haematococcus pluvialis

Summary This study represents the first genome-wide transcriptomic and lipidomic analysis of H. pluvialis to reveal the regulation of astaxanthin biosynthesis and lipid metabolism during the encystment process under high irradiation.

Transcriptome analysis of acclimatory responses to thermal stress in Antarctic algae.

A customized cDNA chip analysis provided the relative expression profiling of 1439 ESTs of Chaetoceros neogracile in culture environments maintained between 4 and 10 degrees C. Among the 1439 probes, 21.5% were differentially regulated (2-fold) by the temperature upshift within three days. Up-regulation was more prominent among cytoprotective genes, whereas down-regulation was featured in photosynthetic genes. A third of the differentially expressed genes had an unknown function or no similarity to known genes, highlighting their potential importance as a resource to identify key players in the acclimation response of polar algae under thermal stress. Our transcriptome analysis also revealed novel aspects of temperature-responsive, coordinated changes in the abundance of specific mRNAs, along with the rapid establishment of molecular homeostasis in polar algae. Unexpectedly, a small set of genes encoding fucoxanthin chlorophyll a/c-binding proteins were rapidly up-regulated by thermal stress, implying that they have different roles other than light harvesting.

The Arabidopsis thaliana GRF-INTERACTING FACTOR gene family plays an essential role in control of male and female reproductive development.

Reproductive success of angiosperms relies on the precise development of the gynoecium and the anther, because their primary function is to bear and to nurture the embryo sac/female gametophyte and pollen, in which the egg and sperm cells, respectively, are generated. It has been known that the GRF-INTERACTING FACTOR (GIF) transcription co-activator family of Arabidopsis thaliana (Arabidopsis) consists of three members and acts as a positive regulator of cell proliferation. Here, we demonstrate that GIF proteins also play an essential role in development of reproductive organs and generation of the gamete cells. The gif1 gif2 gif3 triple mutant, but not the single or double mutants, failed to establish normal carpel margin meristem (CMM) and its derivative tissues, such as the ovule and the septum, resulting in a split gynoecium and no observable embryo sac. The gif triple mutant also displayed severe structural and functional defects in the anther, producing neither microsporangium nor pollen grains. Therefore, we propose that the GIF family of Arabidopsis is a novel and essential component required for the cell specification maintenance during reproductive organ development and, ultimately, for the reproductive competence.

Interference with oxidative phosphorylation enhances anoxic expression of rice α-amylase genes through abolishing sugar regulation

Rice has the unique ability to express α-amylase under anoxic conditions, a feature that is critical for successful anaerobic germination and growth. Previously, anaerobic conditions were shown to up-regulate the expression of Amy3 subfamily genes (Amy3B/C, 3D, and 3E) in rice embryos. These genes are known to be feedback regulated by the hydrolytic products of starchy endosperm such as the simple sugar glucose. It was found that oxygen deficiency interferes with the repression of Amy3D gene expression imposed by low concentrations of glucose but not with that imposed by higher amounts. This differential anoxic de-repression depending on sugar concentration suggests the presence of two distinct pathways for sugar regulation of Amy3D gene expression. Anoxic de-repression can be mimicked by treating rice embryos with inhibitors of ATP synthesis during respiration. Other sugar-regulated rice α-amylase genes, Amy3B/C and 3E, behave similarly to Amy3D. Treatment with a respiratory inhibitor or anoxia also relieved the sugar repression of the rice CIPK15 gene, a main upstream positive regulator of SnRK1A that is critical for Amy3D expression in response to sugar starvation. SnRK1A accumulation was previously shown to be required for MYBS1 expression, which transactivates Amy3D by binding to a cis-acting element found in the proximal region of all Amy3 subfamily gene promoters (the TA box). Taken together, these results suggest that prevention of oxidative phosphorylation by oxygen deficiency interferes with the sugar repression of Amy3 subfamily gene expression, leading to their enhanced expression in rice embryos during anaerobic germination.

Abscisic acid prevents the coalescence of protein storage vacuoles by upregulating expression of a tonoplast intrinsic protein gene in barley aleurone

Tonoplast intrinsic proteins (TIPs) are integral membrane proteins that are known to function in plants as aquaporins. Here, we propose another role for TIPs during the fusion of protein storage vacuoles (PSVs) in aleurone cells, a process that is promoted by gibberellic acid (GA) and prevented by abscisic acid (ABA). Studies of the expression of barley (Hordeum vulgare) TIP genes (HvTIP) showed that GA specifically decreased the abundance of HvTIP1;2 and HvTIP3;1 transcripts, while ABA strongly increased expression of HvTIP3;1. Increased or decreased expression of HvTIP3;1 interfered with the hormonal effects on vacuolation in aleurone protoplasts. HvTIP3;1 gain-of-function experiments delayed GA-induced vacuolation, whereas HvTIP3;1 loss-of-function experiments promoted vacuolation in ABA-treated aleurone cells. These results indicate that TIP plays a key role in preventing the coalescence of small PSVs in aleurone cells. Hormonal regulation of the HvTIP3;1 promoter is similar to the regulation of the endogenous gene, indicating that induction of the transcription of HvTIP3;1 by ABA is a critical factor in the prevention of PSV coalescence in response to ABA. Promoter analysis using deletions and site-directed mutagenesis of sequences identified three cis-acting elements that are responsible for ABA responsiveness in the HvTIP3;1 promoter. Promoter analysis also showed that ABA responsiveness of the HvTIP3;1 promoter is likely to occur via a unique regulatory system distinct from that involving the ABA-response promoter complexes.

Ethylene-induced opposite redistributions of calcium and auxin are essential components in the development of tomato petiolar epinastic curvature.

Calcium has been suggested as an important mediator of gravity signaling transduction within the root cap statocyte. In a horizontally-placed root, it is redistributed in the direction of the gravity vector (i.e. it moves downward) and its redistribution is closely correlated with auxin downward movement. However, the involvement of calcium in the regulation of ethylene-induced epinasty and auxin movement is not known. In this report, we examined the involvement of calcium in lateral auxin transport during ethylene-induced epinasty in an effort to understand the relationship among calcium, auxin, and ethylene. Ethylene-induced epinasty was further stimulated by exogenously applied Ca2+, the calcium effect being the strongest among divalent cations tested. Pretreatment with NPA, an auxin transport inhibitor, negated the promotive effect of calcium ions on the petiolar epinasty. Ethylene caused redistribution/differential accumulation of 45Ca2+ toward the morphologically lower (abaxial) side of the leaf petioles, an effect opposite to that of 14C-IAA redistribution. Verapamil, a Ca2+ channel blocker, inhibited ethylene-induced epinasty, as well as the redistribution of 14C-IAA and 45Ca2+. When the petiole was inverted in the presence or absence of ethylene, the direction of 45Ca2+ differential accumulation was still toward the morphologically abaxial side of the petiole during epinastic movement regardless of gravitational direction. These results suggest that gravity-insensitive, ethylene-induced Ca2+ redistribution and accumulation toward the abaxial side are closely coupled to the adaxial auxin redistribution/accumulation and, in turn, to the petiolar epinasty.

Role of rice cytosolic hexokinase OsHXK7 in sugar signaling and metabolism

We characterized the function of the rice cytosolic hexokinase OsHXK7 (Oryza sativa Hexokinase7), which is highly upregulated when seeds germinate under O2 -deficient conditions. According to transient expression assays that used the promoter:luciferase fusion construct, OsHXK7 enhanced the glucose (Glc)-dependent repression of a rice α-amylase gene (RAmy3D) in the mesophyll protoplasts of maize, but its catalytically inactive mutant alleles did not. Consistently, the expression of OsHXK7, but not its catalytically inactive alleles, complemented the Arabidopsis glucose insensitive2-1 (gin2-1) mutant, thereby resulting in the wild type characteristics of Glc-dependent repression, seedling development, and plant growth. Interestingly, OsHXK7-mediated Glc-dependent repression was abolished in the O2 -deficient mesophyll protoplasts of maize. This result provides compelling evidence that OsHXK7 functions in sugar signaling via a glycolysis-dependent manner under normal conditions, but its signaling role is suppressed when O2 is deficient. The germination of two null OsHXK7 mutants, oshxk7-1 and oshxk7-2, was affected by O2 deficiency, but overexpression enhanced germination in rice. This result suggests the distinct role that OsHXK7 plays in sugar metabolism and efficient germination by enforcing glycolysis-mediated fermentation in O2 -deficient rice.

Comparative transcriptome profiling of developing caryopses from two rice cultivars with differential dormancy

Pre-harvest sprouting (PHS) in rice causes poor grain quality and results in significant reductions in yield, leading to significant economic losses. In contrast, deep dormancy can lead to equally unwanted non-uniform germination. Therefore, a suitable level of dormancy is a critically important agronomic trait. In this study, an analysis of PHS in developing seeds of two Korean rice cultivars (vivipary), Gopum and Samgwang, revealed differences in dormancy in caryopses at 25 d after heading (DAH). To assess the transcriptomic characteristics associated with vivipary, we compared RNA profiles at early (3-6 DAH), middle (25 DAH), and late (40 DAH) developmental stages. Transcriptomic differentiation was most pronounced in caryopses at 25 DAH, the developmental stage at which differential dormancy was also the most prominent. A k-means clustering analysis of the two cultivars revealed groups of genes with similar or dissimilar expression profiles. Many of the genes that showed distinct differential expression profiles were those involved in seed maturation. Intriguingly, differential gene expression levels between the two cultivars were positively correlated with fold-changes in their expression during the early half of caryopsis development. This implies that the establishment of seed dormancy is strongly correlated with the altered transcriptomic patterns related to the progression of maturation. Our global RNA profiling suggests that caryopsis development in Gopum proceeds at a greater speed than in the Samgwang cultivar. Thus, a high degree of maturity and early dormancy release may be present in 25 DAH caryopses of Gopum, although we cannot exclude the possibility of genetic defects modifying dormancy. The comparative transcriptomic analysis of the two cultivars did not reveal noticeable differences in RNA profiles with respect to differences in abscisic acid (ABA) content or ABA sensitivity. Therefore, it is unlikely that ABA is directly involved in the differences in dormancy observed between the two cultivars.

Fabrication of fiber-optic radiation sensor tips with inorganic scintillator for remote sensing of X or /spl gamma/-ray

In this study, fiber-optic radiation sensor tips are fabricated for remote sensing of X or /spl gamma/-ray with inorganic scintillators and plastic optical fiber. The visible range of light from the inorganic scintillator that is generated by radiation source is guided by the plastic optical fiber and is measured by optical detector and power-meter. Two kinds of sensor tips are designed and fabricated such as film type and powder type. Many kinds of inorganic scintillators are used to fabricate both sensor tips, and the different wavelength of emitting lights from them are measured to determine the optimal inorganic scintillator which has maximum light output. As a radiation source, X-ray generator and Ir-192 are selected to test performance of sensor tips. Additionally, fiber-optic radiation sensor tip with organic scintillating fiber is also fabricated and the optical power is measured using the same radiation sources as mentioned above, with inorganic scintillators such as film and powder type briefly.

The Arabidopsis thaliana NGATHA transcription factors negatively regulate cell proliferation of lateral organs

AbstractThe cell proliferation process of aerial lateral organs, such as leaves and flowers, is coordinated by complex genetic networks that, in general, converge on the cell cycle. The Arabidopsis thaliana NGATHA (AtNGA) family comprises four members that belong to the B3-type transcription factor superfamily, and has been suggested to be involved in growth and development of aerial lateral organs, although its role in the cell proliferation and expansion processes remains to be resolved in more detail. In order to clarify the role of AtNGAs in lateral organ growth, we took a systematic approach using both the loss- and gain-of-functional mutants of all four members. Our results showed that overexpressors of AtNGA1 to AtNGA4 developed small, narrow lateral organs, whereas the nga1 nga2 nga3 nga4 quadruple mutant produced large, wide lateral organs. We found that cell numbers of the lateral organs were significantly affected: a decrease in overexpressors and, inversely, an increase in the quadruple mutant. Kinematic analyses on leaf growth revealed that, compared with the wild type, the overexpressors displayed a lower activity of cell proliferation and yet the mutant a higher activity. Changes in expression of cell cycle-regulating genes were well in accordance with the cell proliferation activities, establishing that the AtNGA transcription factors act as bona fide negative regulators of the cell proliferation of aerial lateral organs.