The Arabidopsis thaliana Homeobox Gene ATHB12 Is Involved in Symptom Development Caused by Geminivirus Infection

BACKGROUND: Geminiviruses are single-stranded DNA viruses that infect a number of monocotyledonous and dicotyledonous plants. Arabidopsis is susceptible to infection with the Curtovirus, Beet severe curly top virus (BSCTV). Infection of Arabidopsis with BSCTV causes severe symptoms characterized by stunting, leaf curling, and the development of abnormal inflorescence and root structures. BSCTV-induced symptom development requires the virus-encoded C4 protein which is thought to interact with specific plant-host proteins and disrupt signaling pathways important for controlling cell division and development. Very little is known about the specific plant regulatory factors that participate in BSCTV-induced symptom development. This study was conducted to identify specific transcription factors that are induced by BSCTV infection. METHODOLOGY/PRINCIPAL FINDINGS: Arabidopsis plants were inoculated with BSCTV and the induction of specific transcription factors was monitored using quantitative real-time polymerase chain reaction assays. We found that the ATHB12 and ATHB7 genes, members of the homeodomain-leucine zipper family of transcription factors previously shown to be induced by abscisic acid and water stress, are induced in symptomatic tissues of Arabidopsis inoculated with BSCTV. ATHB12 expression is correlated with an array of morphological abnormalities including leaf curling, stunting, and callus-like structures in infected Arabidopsis. Inoculation of plants with a BSCTV mutant with a defective c4 gene failed to induce ATHB12. Transgenic plants expressing the BSCTV C4 gene exhibited increased ATHB12 expression whereas BSCTV-infected ATHB12 knock-down plants developed milder symptoms and had lower ATHB12 expression compared to the wild-type plants. Reporter gene studies demonstrated that the ATHB12 promoter was responsive to BSCTV infection and the highest expression levels were observed in symptomatic tissues where cell cycle genes also were induced. CONCLUSIONS/SIGNIFICANCE: These results suggest that ATHB7 and ATHB12 may play an important role in the activation of the abnormal cell division associated with symptom development during geminivirus infection

Salt crust development in paddy fields owing to soil evaporation and drainage : contribution of chloride and deuterium profile analysis

In Northeast Thailand lowlands with shallow saline watertable, rainfed paddy fields often present high salt concentration in the dry season, forming patches or spots of salt crusts on the soil surface. In this context, the mechanisms implied in salt concentration during dry season were studied by establishing salt budget with evaporation and drainage estimates inside and outside a saline patch. Drainage was estimated by Hydrus-1D modelling constrained by an hydrodynamic characterization and the profile of water contents at the end of dry season. Evaporation rates at the end of the dry season were computed by interpreting natural detailed profiles of deuterium (D) and chloride (Cl) contents. Because of the drastic diminution of hydraulic conductivity at saturation with depth and the decrease of groundwater level at the end of the cropping season, simulated hydrological balance with Hydrus-1D pointed out zero cumulated fluxes for depths of 39.5 cm (outside the saline patch) and 37.5 cm (inside the saline patch). Therefore, ail the chloride accumulated in the very upper layers during dry season comes from the chloride that was present in the 0-39.5 cm layers before the beginning of the drying. Inside the saline patch, the tentative Cl budget is coherent with the hypothesis of saturation of the profile by aquifer saline water during the flooding. Evaporation rates computed from the diffusion of chloride and deuterium at the end of the drying season, when the aquifer level was 1.4 m deep, range between 0.121 and 0.378 mm d(-1). This does not sustain the assumption of a considerable salinity contribution from the aquifer during the dry season. Moreover, evaporation estimates based on Cl and D diffusion equilibrium showed depleted rates (38-63%) inside the saline patch due to salt accumulation in the first 12 cm of the soil. In the vapour transfer Layer, estimated evaporation rate based on the vapour movement of D was in the same order of magnitude than computed rate assuming liquid Cl diffusion. This coincidence is attributed to the liquid fluxes that occurred during the expansion of the vapour transfer Layer during the progression of the evaporation front

Prdm4 induction by the small molecule butein promotes white adipose tissue browning

Increasing the thermogenic activity of adipocytes holds promise as an approach to combating human obesity and its related metabolic diseases. We identified PR domain containing 4 (Prdm4) induction by the small molecule butein as a means to induce uncoupling protein 1 expression, increase energy expenditure, and stimulate the generation of thermogenic adipocytes. This study highlights a Prdm4-dependent pathway, modulated by small molecules, that stimulates white adipose tissue browning