The molecular mechanism of shade avoidance in crops--How data from Arabidopsis can help to identify targets for increasing yield and biomass production

In order to prevent or counteract shading,plants enact a complex set of growth and developmental adaptations when they sense a change in light quality caused by other plants in their vicinity.This shade avoidance response（SAR）typically includes increased stem elongation at the expense of plant fitness and yield,making it an undesirable trait in an agricultural context.Manipulating the molecular factors involved in SAR can potentially improve productivity by increasing tolerance to higher planting density.However,most of the investigations of the molecular mechanism of SAR have been carried out in Arabidopsis thaliana,and it is presently unclear in how far results of these investigations apply to crop plants.In this review,current data on SAR in crop plants,especially from members of the Solanaceae and Poaceae families,are integrated with data from Arabidopsis,in order to identify the most promising targets for biotechnological approaches.Phytochromes,which detect the change in light caused by neighboring plants,and early signaling components can be targeted to increase plant productivity.However,they control various photomorphogenic processes not necessarily related to shade avoidance.Transcription factors involved in SAR signaling could be better targets to specifically enhance or suppress SAR.Knowledge integration from Arabidopsis and crop plants also indicates factors that could facilitate the control of specific aspects of SAR.Candidates are provided for the regulation of plant architecture,flowering induction and carbohydrate allocation.Yet to-be-elucidated factors that control SAR-dependent changes in biotic resistance and cell wall composition are pointed out.This review also includes an analysis of publicly available gene expression data for maize to augment the sparse molecular data available for this important species.

Toxicity assessment for chlorpyrifos-contaminated soil with three different earthworm test methods

Earthworm toxicity tests are useful tools for terrestrial risk assessment but require a hierarchy of test designs that differ in effect levels （behavior, sublethal, lethal）. In this study, the toxicity of chlorpyrifos contaminated soil on earthworms was assessed. In addition to the acute and chronic tests, an avoidance response test was applied. Earthworms were exposed to sublethal and lethal concentration of chlorpyrifos, and evaluated for acute toxicity, growth, fecundity and avoidance response after a certain exposure period. The test methods covered all important ecological relevant endpoints （acute, chronic, behavioral）. Concentration of 78.91 mg/kg, chlorpyrifos caused significant toxic effects in all test methods, but at lower test concentrations, only significant chronic toxic effects could be observed. In present study, chlorpyrifos had adverse effect on growth and fecundity in earthworm exposed to 5 mg/kg chlorpyrifos after eight weeks. The avoidance response test, however, showed significant repellent effects at concentration of 40 mg/kg chlorpyrifos. For chlorpyrifos, concentration affecting avoidance response was far greater than growth and fecundity, it seemed likely that earthworms were not able to escape from pesticide-contaminated soil into the clean soil in field and hence were exposed continuously to elevated concentrations of pesticides.

Assessing cypermethrin-contaminated soil with three different earthworm test methods

A series of tests (lethal,sublethal,and behavioral) on earthworms were conducted as an eco-assessment of pesticides.In this study,the toxicity of cypermethrin-contaminating soil on adult and juvenile earthworms was assessed.Beside the acute and chronic tests,an avoidance response test was carried out.It was shown that the all-round toxicity from cypermethrin was weak on adult earthworms.Compared with adult earthworms,the toxicity of juvenile earthworms from cypermethrin especially chronic toxicity increased...

Carbon Nanoparticle Exerts Positive Growth Effects with Increase in Productivity by Down-Regulating Phytochrome B and Enhancing Internal Temperature in Rice

The effects of carbon nanoparticle(CNP)on rice variety Swarna(MTU7029)were investigated.CNP induced effects similar to shade avoidance response(SAR)of Arabidopsis,with increase in shoot length,root length,root number,cotyledon area,chlorophyll content and total sugar content in rice seedlings.In mature plants,CNP treatment resulted increase in plant height,number of productive tillers per plant,normalized difference vegetation index,quantum yield and root growth.A total of 320 mg of CNP per plant administered in four doses resulted in improved grain traits such as filled grain rate,100-grain weight,grain length/width ratio,hulling rate,milling rate and head rice recovery.Seeds from the CNP-treated plants showed increase in amylose,starch and soluble sugar contents compared to controls.Strikingly,CNP treatment showed an average of 17.5%increase in yield per plant.Upon investigation to the molecular mechanism behind CNP induction of SAR,a significant downregulation of phytochrome B transcript was found.Decrease in perception of red wavelengths led to responses similar to SAR.Increase in plant’s internal temperature by 0.5ºC±0.1ºC was recorded after CNP treatment.We suggest that the internalized CNP aggregates may serve to absorb extra photons thereby increasing the internal temperature of plants.Phytochrome B accounts the hike in internal temperature and initiates a feed-back reduction of its own transcription.We suggest that moderate SAR is beneficial for rice plants to improve agronomic traits and yield.It presents a potential non-transgenic method for improving rice yield by CNP treatment.

Jamming Avoidance Response Inspired by Wave-type WeaMy Electric Fish

Weakly electric fish use the electric field to detect objects in the neighborhood or communicate with conspecifics. They generate electric field with their electric organ and the electroreceptors sense the distortion of electric field caused by nearby objects. They use a modulated frequency signal of the Electric Organ Discharge （EOD）, and it can be disturbed by similar frequency signals that neighboring weakly electric fish emit. They have a particular behavior response to change their EOD frequencies to avoid signal jamming. It is called jamming avoidance response. Inspired by the behavior of wave-type weakly electric fish, we propose an engineering perspective of jamming avoidance response model with the amplitude-phase modulation graph. The time course of the amplitude-phase graph of the EOD signal provides a cue to detect the jamming signal. We argue that the temporal integration can determine the shift direction of the EOD as well as the amount of the frequency shift to be moved frequency for the jamming avoidance response. Alternatively, as a fast adapting measure, the cross product of point vectors in the amplitude-phase graph allows early decision for jamming avoidance. We demonstrate the methods with simulations and the real experiments in the underwater environment.

Shade-induced stem elongation in rice seedlings:Implication of tissue-specific phytohormone regulation

Summary A better understanding of shade avoidance syndrome （SAS） is an urgent need because of its effect on energy reallocation. Leverage-related mechanism in crops is of potential economic interest for agricultural applications. Here we report the SAS phenotype at tissue level rice seedlings. Tissue-specific RNA-sequencing indicates auxin plays different roles between coleoptile and the first leaf. Phenotypes of wild type treated by gibberellin and brassinosteroid biosynthesis inhibitors and of related mutants suggest these two hormones positively regulate SAS. Our work reveals the diversity of hormone responses in different organs and different species in shade conditions.

Blue-light-induced rapid chloroplast de-anchoring in Vallisneria epidermal cells

In the outer periclinal cytoplasm of leaf epidermal cells of an aquatic angiosperm Vallisneria, blue light induces ＂chloroplast de-anchoring＂, a rapid decline in the resistance of chloroplasts against centrifugal force. Chloroplast de- anchoring is known induced within lmin of irradiation with high-fluence-rate blue light specifically, preceding the com- mencement of chloroplasts migration toward the anticlinal cytoplasm. However, its regulatory mechanism has remained elusive, although pharmacological analysis suggested that a calcium release from intracellular calcium stores is necessary for the response, in search of the responsible photoreceptors, immunoblotting analysis using antibodies against phototropins demonstrated that cross-reactive polypeptides of 120-kDa exist in the plasma-membrane fraction prepared from the leaves. In vitro phosphorylation analysis revealed that 120-kDa polypeptides were phosphorylated by exposure to blue light in a fluence-dependent manner. The blue-light-induced phosphorylation activity was sensitive to a Ser/Thr kinase inhibitor, staurosporine, and unusually was retained at a high level for a long time in darkness. Furthermore, phototropin gene homologs （Vallisneria PHOTOTROPINI and PHOTOTROPIN2） expressed in leaves were isolated. We propose that calcium- regulated chloroplast de-anchoring, possibly mediated by phototropins, is an initial process of the blue-light-induced avoidance response of chloroplasts in Vallisneria.