Algal glycobiotechnology: omics approaches for strain improvement

Microalgae has the capability to replace petroleum-based fuels and is a promising option as an energy feedstock because of its fast growth, high photosynthetic capacity and remarkable ability to store energy reserve molecules in the form of lipids and starch. But the commercialization of microalgae based product is difficult due to its high processing cost and low productivity. Higher accumulation of these molecules may help to cut the processing cost. There are several reports on the use of various omics techniques to improve the strains of microalgae for increasing the productivity of desired products. To effectively use these techniques, it is important that the glycobiology of microalgae is associated to omics approaches to essentially give rise to the field of algal glycobiotechnology. In the past few decades, lot of work has been done to improve the strain of various microalgae such as Chlorella, Chlamydomonas reinhardtii, Botryococcus braunii etc., through genome sequencing and metabolic engineering with major focus on significantly increasing the productivity of biofuels, biopolymers, pigments and other products. The advancements in algae glycobiotechnology have highly significant role to play in innovation and new developments for the production algae-derived products as above. It would be highly desirable to understand the basic biology of the products derived using -omics technology together with biochemistry and biotechnology. This review discusses the potential of different omic techniques (genomics, transcriptomics, proteomics, metabolomics) to improve the yield of desired products through algal strain manipulation.

Arundo Donax L.: How High Photosynthetic Capacity is Maintained under Water Scarcity Conditions

Arundo donax L. (giant reed) is a perennial rhizomatous grass and has been identified as an important non-food biomass crop with capacity for cultivation in marginal and degraded lands where water scarcity conditions frequently occur due to climate change. This review analyzes the effect of water stress on photosynthetic capacity and biomass production in multiple giant reed ecotypes grown in different regions around the world. Furthermore, this review will attempt to explain the reason for the high photosynthetic capacity of giant reed even under changing environmental conditions as well as indicate other morphological reasons that could contribute to maintaining this high photosynthetic rate. Finally, future research in favor of selecting ecotypes with drought tolerance is proposed.

Diverse Physiological and Physical Responses among Wild, Landrace and Elite Barley Varieties Point to Novel Breeding Opportunities

Climate change from elevated [CO2] may reduce water availability to crops through changes in precipitation and higher temperatures. However, agriculture already accounts for 70% of human consumption of water. Stomata, pores in the leaf surface, mediate exchange of water and CO2 for the plant. In crops including barley, the speed of stomatal response to changing environmental conditions is as important as maximal responses and can thus affect water use efficiency. Wild barleys and landraces which predate modern elite lines offer the breeder the potential to find unexploited genetic diversity. This study aimed to characterize natural variation in stomatal anatomy and leaf physiology and to link these variations to yield. Wild, landrace and elite barleys were grown in a polytunnel and a controlled environment chamber. Physiological responses to changing environments were measured, along with stomatal anatomy and yield. The elite barley lines did not have the fastest or largest physiological responses to light nor always the highest yields. There was variation in stomatal anatomy, but no link between stomatal size and density. The evidence suggests that high photosynthetic capacity does not translate into yield, and that landraces and wild barleys have unexploited physiological responses that should interest breeders.

MdTyDc Overexpression Improves Alkalinity Tolerance in Malus domestica

Tyrosine is decarboxylated to tyramine by TYDC (Tyrosine decarboxylase) and then hydroxylated to dopamine, which is involved in plant response to abiotic stress. However, little is known about the function of MdTyDc in response to alkaline stress in plants. In our study, it was found that the expression of MdTyDc was induced by alkaline stress. Therefore, the apple plants overexpressing MdTyDc was treated with alkali stress, and we found that MdTyDc played an important role in apple plants’ resistance to alkali stress. Our results showed that the restriction on the growth, the decrease of membrane permeability and the accumulation of Na+ were alleviated to various degrees in MdTyDc transgenic plants under alkali stress. In addition, overexpression of MdTyDc enhanced the root activity and photosynthetic capacity, and improved the enzyme activity related to N metabolism, thus promoting N absorption. It is noteworthy that the dopamine content of these three transgenic lines is significantly higher than that of WT. In summary, these findings indicated that MdTyDc may enhance alkaline tolerance of apples by mediating dopamine content, mainly by maintaining high photosynthetic capacity, normal ion homeostasis and strong nitrogen absorption capacity.

Low photorespiratory capacity is sufficient to block the induction of photosynthetic capacity in high light

The induction of high photosynthetic capacity in high light (HL) is a common response among many herbaceous dicot plants, however, the signals that control this response remain largely unknown. Here, multiple independent lines of evidence are presented in support of the conclusion that low photorespiratory capacity acts a negative signal to limit photosynthetic capacity acclimation in HL in Arabidopsis thaliana. Using a panel of natural accessions, primary nitrogen (N) assimilation and photorespiration rates early after a shift to growth in HL, as well as activities for key enzymes in these pathways, were shown to positively correlate with the magnitude of the subsequent induction of photosynthetic capacity, which occurred several days later. Time-resolved metabolomic data during acclimation to HL were collected using a strongly acclimating ecotype and a weakly acclimating ecotype, revealing in greater detail the differences in N assimilation, photorespiration, and triose-phosphate utilization pathways underlying efficient photosynthetic capacity acclimation. When shifted into HL growth conditions under non-photorespiratory conditions, weakly acclimating ecotypes and even photorespiratory mutants gained the ability to strongly induce high photosynthetic capacity in HL. Thus, a negative, photorespiration-dependent signal early in the HL shift appears to block photosynthetic capacity acclimation in accessions with low photorespiratory capacity, whereas accessions with high photorespiratory capacity are licensed to increase photosynthetic capacity.

Duration of Weed Presence Influences the Recovery of Photosynthetic Efficiency and Yield in Common Bean (Phaseolus vulgaris L.)

Photosynthetic responses of common bean (Phaseolus vulgaris L.) to increasing durations of weed-free and weedy environments were investigated using a critical period for weed control study under field conditions. The presence of weeds induced the shade avoidance response and was accompanied by a reduced red to far-red ratio (R/Fr) of reflected light supporting previous assertions it is an important signal regulating crop-weed interactions. Despite increases in stomatal conductance and leaf intercellular [CO2] with increasing duration of weed presence, CO2 assimilation and photosynthetic efficiency continually declined. This coincided with reduced Calvin cycle capacity suggesting induction of biochemical rather than stomatal limitations on photosynthesis. Weed removal prior to reproductive stages resulted in maintenance of high photosynthetic capacity. When weed presence extended to reproductive stages and beyond the critical period for weed control, however, CO2 assimilation and photosynthetic efficiency never recovered. Yield was highly correlated with photosynthetic efficiency and in a similar manner, declined with increasing durations of weed presence through reduced seeds per plant. We conclude that the lasting consequence of weed competition is impairment of photosynthesis, which may provide an important mechanism to explain yield loss.

Down-regulation of the Genome Uncoupled 4 Retards Starch Biosynthesis in Rice

BackgroundStarch is the major storage carbohydrate in rice, with essential physical functions for plant growth. The starch biosynthesis in rice employs the cooperation of nucleus and plastid, which requires regulation of the signals from nucleus to plastid. However, the plastid-to-nucleus retrograde signals for starch biosynthesis is partly mediated by tetrapyrrole intermediates, i.e., heme, but the underlying mechanism is largely unknown. In previous studies, we revealed that the Genome Uncoupled 4 (OsGUN4) mutation in rice have been revealed to greatly affect tetrapyrrole intermediates but retain a high photosynthetic capacity. ResultsHere, we further found that down-regulation of OsGUN4 promoted to accumulate sucrose but reduce the total starch, attributing to abnormal performance of metabolisms and enzyme activities of starch biosynthesis in leaves of gun4epi. Besides, the exogenous sucrose led to induced starch synthesis but reduced sucrose contents in wild-type, while norflurazon(NF) treatments could eliminate or weaken these inductions. Nevertheless, no changes were detectedbetween check and sucrose treatments in the gun4epi,whereas NF treatment enhanced the trends of increased sucrose but reduced starch,suggesting the roles of OsGUN4 on balance of photosynthesis and starch biosynthesis. Dynamic activity changes of starch biosynthetic enzymes were in accordance with the contents of carbon metabolites. Moreover, RNA sequencing revealed that a great deal DEGs were associated with starch metabolic pathways, with 62 genes being up-regulated and 25 down-regulated in gun4epi. Many genes involved in starch biosynthesis performed down-regulated expression, including the transcription factor of bZIP58 and its target genes of OsBEIIb and OsSSI, which are vital for the formation of amylopectin and starch granules, while displayed up-regulatedexpression of OsSSIIIa and OsGBSSI that promotes the formation of amylose. ConclusionIn conclusion, these findings confirm that OsGUN4 play regulatory roles on biosynthetic genes and enzyme activity in starch biosynthesis.

Leaf-scale quantification of the effect of photosynthetic gas exchange on Δ17O of atmospheric CO2

<p> </p><p> </p><p>Understanding the processes affecting the triple oxygen isotope composition of atmospheric CO<sub>2</sub> during photosynthesis can help to constrain the interaction and fluxes between the atmosphere and the biosphere. We conducted leaf cuvette experiments under controlled conditions, using sunflower (<em>Helianthus annuus</em>), an annual C<sub>3</sub> species with high photosynthetic capacity and stomatal conductance for CO<sub>2</sub>, an evergreen C<sub>3</sub> species, ivy (<em>Hedera hybernica</em>) with lower values for these traits, and a C<sub>4</sub> species maize (<em>Zea mays)</em> that has a high photosynthetic capacity and low stomatal conductance. The experiments were conducted at different light intensities and using CO<sub>2</sub> with different <sup>17</sup>O- excess. Our results demonstrate that two key factors determine the effect of photosynthetic gas exchange on Δ<sup>17</sup>O of atmospheric CO<sub>2</sub>: The relative difference in Δ<sup>17</sup>O of the CO<sub>2</sub> entering the leaf and Δ<sup>17</sup>O of leaf water, and the back-diffusion flux from the leaf to the atmosphere, which can be quantified by the c<sub>m</sub>/c<sub>a</sub> ratio.  At low c<sub>m</sub>/c<sub>a</sub> the discrimination is governed by diffusion into the leaf, and at high c<sub>m</sub>/c<sub>a</sub> by back-diffusion of CO<sub>2</sub> that has equilibrated with the leaf water. Plants with a higher c<sub>m</sub>/c<sub>a</sub> ratio modify the Δ<sup>17</sup>O of atmospheric CO<sub>2</sub> more strongly than plants with lower c<sub>m</sub>/c<sub>a</sub>. </p><p>Based on the leaf cuvette experiments using both C<sub>4</sub> and C<sub>3</sub> plants, the global discrimination in <sup>17</sup>O-excess of atmospheric CO<sub>2</sub> due to assimilation is estimated to be -0.6±0.2‰. The main uncertainty in the global estimation is due to the uncertainty in the c<sub>m</sub>/c<sub>a</sub> ratio.</p><p> </p><p> </p><p> </p>