CO2 uptake and chlorophyll a fluorescence of Suaeda fruticosa grown under diurnal rhythm and after transfer to continuous dark

A cystathionine beta-synthase domain containing protein, OsCBSCBS4, interacts with OsSnRK1A and OsPKG and functions in abiotic stress tolerance in rice

The Cystathionine-β-Synthase (CBS) domain-containing proteins (CDCPs) constitute a functionally diverse protein superfamily, sharing an evolutionary conserved CBS domain either in pair or quad. Rice genome (Oryza sativa subsp. indica) encodes 42 CDCPs; their functions remain largely unexplored. This study examines OsCBSCBS4, a quadruple CBS domain containing protein towards its role in regulating the abiotic stress tolerance in rice. Gene expression analyses revealed upregulation of OsCBSCBS4 in response to diverse abiotic stresses. Further, the cytoplasm-localised OsCBSCBS4 showed interaction with two different kinases, a cytoplasmic localised cGMP-dependant protein kinase (OsPKG) and the nucleo-cytoplasmic catalytic subunit of sucrose-nonfermentation 1-related protein kinase 1 (OsSnRK1A). The interaction with the latter assisted in trafficking of OsCBSCBS4 to the nucleus as well. Overexpression of OsCBSCBS4 in rice resulted in enhanced tolerance to drought and salinity stress, via maintaining better physiological parameters and antioxidant activity. Additionally, OsCBSCBS4-overexpressing rice plants exhibited reduced yield penalty under stress conditions. The in silico docking and in vitro binding analyses of OsCBSCBS4 with ATP suggest its involvement in cellular energy balance. Overall, this study provides novel insight into the unexplored functions of OsCBSCBS4 and demonstrates it as a new promising target for augmenting crop resilience.

Thriving under Salinity: Growth, Ecophysiology and Proteomic Insights into the Tolerance Mechanisms of Obligate Halophyte Suaeda fruticosa

Studies on obligate halophytes combining eco-physiological techniques and proteomic analysis are crucial for understanding salinity tolerance mechanisms but are limited. We thus examined growth, water relations, ion homeostasis, photosynthesis, oxidative stress mitigation and proteomic responses of an obligate halophyte Suaeda fruticosa to increasing salinity under semi-hydroponic culture. Most biomass parameters increased under moderate (300 mmol L-1 of NaCl) salinity, while high (900 mmol L-1 of NaCl) salinity caused some reduction in biomass parameters. Under moderate salinity, plants showed effective osmotic adjustment with concomitant accumulation of Na+ in both roots and leaves. Accumulation of Na+ did not accompany nutrient deficiency, damage to photosynthetic machinery and oxidative damage in plants treated with 300 mmol L-1 of NaCl. Under high salinity, plants showed further decline in sap osmotic potential with higher Na+ accumulation that did not coincide with a decline in relative water content, Fv/Fm, and oxidative damage markers (H2O2 and MDA). There were 22, 54 and 7 proteins in optimal salinity and 29, 46 and 8 proteins in high salinity treatment that were up-regulated, down-regulated or exhibited no change, respectively, as compared to control plants. These data indicate that biomass reduction in S. fruticosa at high salinity might result primarily from increased energetic cost rather than ionic toxicity.

A glutathione-independent DJ-1/Pfp1 domain containing glyoxalase III, OsDJ-1C, functions in abiotic stress adaptation in rice

MAIN CONCLUSION

Overexpression of OsDJ-1C in rice improves root architecture, photosynthesis, yield and abiotic stress tolerance through modulating methylglyoxal levels, antioxidant defense, and redox homeostasis. Exposure to abiotic stresses leads to elevated methylglyoxal (MG) levels in plants, impacting seed germination and root growth. In response, the activation of NADPH-dependent aldo-keto reductase and glutathione (GSH)-dependent glyoxalase enzymes helps to regulate MG levels and reduce its toxic effects. However, detoxification may not be carried out effectively due to the limitation of GSH and NADPH in plants under stress. Recently, a novel enzyme called glyoxalase III (GLY III) has been discovered which can detoxify MG in a single step without needing GSH. To understand the physiological importance of this pathway in rice, we overexpressed the gene encoding GLYIII enzyme (OsDJ-1C) in rice. It was observed that OsDJ-1C overexpression in rice regulated MG levels under stress conditions thus, linked well with plants' abiotic stress tolerance potential. The OsDJ-1C overexpression lines displayed better root architecture, improved photosynthesis, and reduced yield penalty compared to the WT plants under salinity, and drought stress conditions. These plants demonstrated an improved GSH/GSSG ratio, reduced level of reactive oxygen species, increased antioxidant capacity, and higher anti-glycation activity thereby indicating that the GLYIII mediated MG detoxification plays a significant role in plants' ability to reduce the impact of abiotic stress. Furthermore, these findings imply the potential of OsDJ-1C in crop improvement programs.

Impact of individual, combined and sequential stress on photosynthesis machinery in rice (Oryza sativa L)

Abiotic stresses such as heat, drought and submergence are major threats to global food security. Despite simultaneous or sequential occurrence of these stresses being recurrent under field conditions, crop response to such stress combinations is poorly understood. Rice is a staple food crop for the majority of human beings. Exploitation of existing genetic diversity in rice for combined and/or sequential stress is a useful approach for developing climate-resilient cultivars. We phenotyped ~400 rice accessions under high temperature, drought, or submergence and their combinations. A cumulative performance index revealed Lomello as the best performer across stress and stress combinations at the seedling stage. Lomello showed a remarkable ability to maintain a higher quantum yield of photosystem (PS) II photochemistry. Moreover, the structural integrity of the photosystems, electron flow through both PSI and PSII and the ability to protect photosystems against photoinhibition were identified as the key traits of Lomello across the stress environments. A higher membrane stability and an increased amount of leaf chlorophyll under stress may be due to an efficient management of reactive oxygen species (ROS) at the cellular level. Further, an efficient electron flow through the photosystems and, thus, a higher photosynthetic rate in Lomello is expected to act as a sink for ROS by reducing the rate of electron transport to the high amount of molecular oxygen present in the chloroplast. However, further studies are needed to identify the molecular mechanism(s) involved in the stability of photosynthetic machinery and stress management in Lomello during stress conditions.

DTH8 overexpression induces early flowering, boosts yield, and improves stress recovery in rice cv IR64

Rice yield and heading date are the two discrete traits controlled by quantitative trait loci (QTLs). Both traits are influenced by the genetic make-up of the plant as well as the environmental factors where it thrives. Drought and salinity adversely affect crop productivity in many parts of the world. Tolerance to these stresses is multigenic and complex in nature. In this study, we have characterized a QTL, DTH8 (days to heading) from Oryza sativa L. cv IR64 that encodes a putative HAP3/NF-YB/CBF subunit of CCAAT-box binding protein (HAP complex). We demonstrate DTH8 to be positively influencing the yield, heading date, and stress tolerance in IR64. DTH8 up-regulates the transcription of RFT1, Hd3a, GHD7, MOC1, and RCN1 in IR64 at the pre-flowering stage and plays a role in early flowering, increased number of tillers, enhanced panicle branching, and improved tolerance towards drought and salinity stress at the reproductive stage. The presence of DTH8 binding elements (CCAAT) in the promoter regions of all of these genes, predicted by in silico analysis of the promoter region, indicates the regulation of their expression by DTH8. In addition, DTH8 overexpressing transgenic lines showed favorable physiological parameters causing less yield penalty under stress than the WT plants. Taken together, DTH8 is a positive regulator of the network of genes related to early flowering/heading, higher yield, as well as salinity and drought stress tolerance, thus, enabling the crops to adapt to a wide range of climatic conditions.

Ion transporters and their regulatory signal transduction mechanisms for salinity tolerance in plants

Soil salinity is one of the most serious threats to plant growth and productivity. Due to global climate change, burgeoning population and shrinking arable land, there is an urgent need to develop crops with minimum reduction in yield when cultivated in salt-affected areas. Salinity stress imposes osmotic stress as well as ion toxicity, which impairs major plant processes such as photosynthesis, cellular metabolism, and plant nutrition. One of the major effects of salinity stress in plants includes the disturbance of ion homeostasis in various tissues. In the present study, we aimed to review the regulation of uptake, transport, storage, efflux, influx, and accumulation of various ions in plants under salinity stress. We have summarized major research advancements towards understanding the ion homeostasis at both cellular and whole-plant level under salinity stress. We have also discussed various factors regulating the function of ion transporters and channels in maintaining ion homeostasis and ionic interactions under salt stress, including plant antioxidative defense, osmo-protection, and osmoregulation. We further elaborated on stress perception at extracellular and intracellular levels, which triggers downstream intracellular-signaling cascade, including secondary messenger molecules generation. Various signaling and signal transduction mechanisms under salinity stress and their role in improving ion homeostasis in plants are also discussed. Taken together, the present review focuses on recent advancements in understanding the regulation and function of different ion channels and transporters under salt stress, which may pave the way for crop improvement.

Physiological and molecular signatures reveal differential response of rice genotypes to drought and drought combination with heat and salinity stress

Rice is the staple food for more than 3.5 billion people worldwide. The sensitivity of rice to heat, drought, and salinity is well documented. However, rice response to combinations of these stresses is not well understood. A contrasting set of rice genotypes for heat (N22, Gharib), drought (Moroberekan, Pusa 1121) and salinity (Pokkali, IR64) were selected to characterize their response under drought, and combination of drought with heat and salinity at the sensitive seedling stage. Sensitive genotypes (IR64, Pusa 1121, Gharib) recorded higher reactive oxygen species accumulation (20-40%), membrane damage (8-65%) and reduction in photosynthetic efficiency (10-23%) across the stress and stress combinations as compared to stress tolerant checks. On the contrary, N22 and Pokkali performed best under drought + heat, and drought + salinity combination, respectively. Moreover, gene expression pattern revealed the highest expression of catalase (CAT), ascorbate peroxidase (APX) and GATA28a in N22 under heat + drought, whereas the highest expression of CAT, APX, superoxide dismutase (SOD), DEHYDRIN, GATA28a and GATA28b in Pokkali under drought + salinity. Interestingly, the phenotypic variation and expression level of genes highlighted the role of different set of physiological traits and genes under drought and drought combination with heat and salinity stress. This study reveals that rice response to stress combinations was unique with rapid readjustment at physiological and molecular levels. Moreover, phenotypic changes under stress combinations showed substantial adaptive plasticity in rice, which warrant further investigations at molecular level.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-022-01162-y.

Stress-Responsive cis-Regulatory Elements Underline Podophyllotoxin Biosynthesis and Better Performance of Sinopodophyllum hexandrum Under Water Deficit Conditions

Sinopodophyllum hexandrum is an endangered medicinal herb known for its bioactive lignan podophyllotoxin (PTOX), which is used for the preparation of anticancer drugs. In its natural habitat, S. hexandrum is exposed to a multitude of adversities, such as fluctuating temperatures, water deficit, and high UV radiations. Transcriptional regulation of genes, which is regulated by the condition-specific binding of transcriptional factors to precise motifs in the promoter region, underlines responses to an environmental cue. Therefore, analysis of promoter sequences could ascertain the spatio-temporal expression of genes and overall stress responses. Unavailability of genomic information does not permit such analysis in S. hexandrum, especially on regulation of PTOX pathway. Accordingly, this study describes isolation and in silico analysis of 5'-upstream regions of ShPLR (PINORESINOL-LARICIRESINOL REDUCTASE) and ShSLD (SECOISOLARICIRESINOL DEHYDROGENASE), the two key genes of the PTOX biosynthetic pathway. Data showed a range of motifs related to basal transcription, stress-responsive elements, such as those for drought, low temperature, and light, suggesting that the expression of these genes and resulting PTOX accumulation would be affected by, at least, these environmental cues. While the impact of temperature and light on PTOX accumulation is well studied, the effect of water deficit on the physiology of S. hexandrum and PTOX accumulation remains obscure. Given the presence of drought-responsive elements in the promoters of the key genes, the impact of water deficit on growth and development and PTOX accumulation was studied. The results showed decline in relative water content and net photosynthetic rate, and increase in relative electrolyte leakage with stress progression. Plants under stress exhibited a reduction in transpiration rate and chlorophyll content, with a gradual increase in osmoprotectant content. Besides, stressed plants showed an increase in the expression of genes involved in the phenylpropanoid pathway and PTOX biosynthesis, and an increase in PTOX accumulation. Upon re-watering, non-irrigated plants showed a significant improvement in biochemical and physiological parameters. Summarily, our results demonstrated the importance of osmoprotectants during water deficit and the revival capacity of the species from water deficit, wherein PTOX synthesis was also modulated. Moreover, isolated promoter sequences could be employed in genetic transformation to mediate the expression of stress-induced genes in other plant systems.

Rewilding staple crops for the lost halophytism: Toward sustainability and profitability of agricultural production systems

Abiotic stress tolerance has been weakened during the domestication of all major staple crops. Soil salinity is a major environmental constraint that impacts over half of the world population; however, given the increasing reliance on irrigation and the lack of available freshwater, agriculture in the 21st century will increasingly become saline. Therefore, global food security is critically dependent on the ability of plant breeders to create high-yielding staple crop varieties that will incorporate salinity tolerance traits and account for future climate scenarios. Previously, we have argued that the current agricultural practices and reliance on crops that exclude salt from uptake is counterproductive and environmentally unsustainable, and thus called for a need for a major shift in a breeding paradigm to incorporate some halophytic traits that were present in wild relatives but were lost in modern crops during domestication. In this review, we provide a comprehensive physiological and molecular analysis of the key traits conferring crop halophytism, such as vacuolar Na⁺ sequestration, ROS desensitization, succulence, metabolic photosynthetic switch, and salt deposition in trichomes, and discuss the strategies for incorporating them into elite germplasm, to address a pressing issue of boosting plant salinity tolerance.

Natural variation in the fast phase of chlorophyll a fluorescence induction curve (OJIP) in a global rice minicore panel

Photosynthesis can be probed through Chlorophyll a fluorescence induction (FI), which provides detailed insight into the electron transfer process in Photosystem II, and beyond. Here, we have systematically studied the natural variation of the fast phase of the FI, i.e. the OJIP phase, in rice. The OJIP phase of the Chl a fluorescence induction curve is referred to as "fast transient" lasting for less than a second; it is obtained after a dark-adapted sample is exposed to saturating light. In the OJIP curve, "O" stands for "origin" (minimal fluorescence), "P" for "peak" (maximum fluorescence), and J and I for inflection points between the O and P levels. Further, F_o is the fluorescence intensity at the "O" level, whereas F_m is the intensity at the P level, and F_v (= F_m - F_o) is the variable fluorescence. We surveyed a set of quantitative parameters derived from the FI curves of 199 rice accessions, grown under both field condition (FC) and growth room condition (GC). Our results show a significant variation between Japonica (JAP) and Indica (IND) subgroups, under both the growth conditions, in almost all the parameters derived from the OJIP curves. The ratio of the variable to the maximum (F_v/F_m) and of the variable to the minimum (F_v/F_o) fluorescence, the performance index (PI_abs), as well as the amplitude of the I-P phase (A_I-P) show higher values in JAP compared to that in the IND subpopulation. In contrast, the amplitude of the O-J phase (A_O-J) and the normalized area above the OJIP curve (S_m) show an opposite trend. The performed genetic analysis shows that plants grown under GC appear much more affected by environmental factors than those grown in the field. We further conducted a genome-wide association study (GWAS) using 11 parameters derived from plants grown in the field. In total, 596 non-unique significant loci based on these parameters were identified by GWAS. Several photosynthesis-related proteins were identified to be associated with different OJIP parameters. We found that traits with high correlation are usually associated with similar genomic regions. Specifically, the thermal phase of FI, which includes the amplitudes of the J-I and I-P subphases (A_J-I and A_I-P) of the OJIP curve, is, in turn, associated with certain common genomic regions. Our study is the first one dealing with the natural variations in rice, with the aim to characterize potential candidate genes controlling the magnitude and half-time of each of the phases in the OJIP FI curve.

Tolerance and decolorization potential of duckweed (Lemna gibba) to C.I. Basic Green 4

With growing human culture and industrialization, many pollutants are being introduced into aquatic ecosystems. In recent years, dyes have become a major water pollutant used in the manufacture of paints and other production purposes. In this research, the potential of duckweed (Lemna gibba) plant was investigated spectrophotometrically as an obvious bioagent for the biological decolorization of the organic dye C.I. Basic Green 4 (Malachite Green, BG4). Photosynthetic efficiency analysis showed that the photosynthetic apparatus of L. gibba is very tolerant to BG4. Significant induction of reactive oxygen species (ROS) scavenging enzymes was observed after 24h of biodecolorization process in L. gibba treated with 15 and 30 mg/l BG4. The experimental results showed that L. gibba has a strong ability to extract BG4 from contaminated water and the best results were obtained at 25–30°C and pH 8.0. We conclude that duckweed L. gibba can be used as a potent decolorization organism for BG4.

Endosphere Microbiome and Metabolic Differences Between the Spots and Green Parts of Tricyrtis macropoda Leaves

Background

Plant leaves are important organs for photosynthesis and biological energy production. The leaves of Tricyrtis macropoda have an unusual spotted pattern. However, whether the spots of T. macropoda affect the plant microbiome and metabolites is unclear. In this study, we compared differences in the endosphere microbiome and plant metabolites in green parts and spots and the effects of spots on the photosynthesis of leaves.

Methods

16S/ITS sequences and metabolite spectra were obtained by high-throughput amplicon sequencing and ultra-high-performance liquid chromatography–high-resolution mass spectrometry, respectively. Changes in the diversity of the endophytic microbial community and metabolites were studied, and the effect of T. macropoda leaf spots on photosynthesis was examined by chlorophyll fluorescence.

Results

The results showed that the relative abundance of Cercospora fungi in the leaf spots of T. macropoda was significantly higher than that in the green parts (P < 0.05) while Colletotrichum fungi showed low abundance in the spots. Alkaloid and ketone metabolites were decreased in the green parts compared with the spots, and amino acids, organic acids, lipids, and other compounds were increased in the green parts compared with the spots. A combined analysis of microbial communities and metabolites showed a significant correlation between the endophytic fungal communities and metabolite production. The changes in these metabolites may cause changes in local leaf color. In addition, we found that the spot areas of T. macropoda can be photosynthetically normal.

Conclusion

This research showed the relationship between endophytic microorganisms and metabolites, and the findings advance our understanding of endophyte–plant interactions and provide a new direction for investigating the relationship between endophytes and phenotypes.

Morphological and physiological factors contributing to early vigor in the elite rice cultivar 9,311

Huanghuazhan (HHZ) and 9,311 are two elite rice cultivars in China. They have achieved high yield through quite different mechanisms. One of the major features that gives high yield capacity to 9,311 is its strong early vigor, i.e., faster establishment of its seedling as well as its better growth in its early stages. To understand the mechanistic basis of early vigor in 9,311, as compared to HHZ the cultivar, we have examined, under controlled environmental conditions, different morphological and physiological traits that may contribute to its early vigor. Our results show that the fresh weight of the seeds, at germination, not only determined the seedling biomass at 10 days after germination (DAG), but was also responsible for ~ 80% of variations in plant biomass between the two cultivars even up to 30 DAG. Furthermore, the 9,311 cultivar had a larger root system, which led to its higher nitrogen uptake capacity. Other noteworthy observations about 9,311 being a better cultivar than HHZ are: (i) Ten out of 15 genes involved in nitrogen metabolism were much more highly expressed in its roots; (ii) it had a higher water uptake rate, promoting better root-to-shoot nitrogen transfer; and (iii) consistent with the above, it had higher leaf photosynthetic rate and stomatal conductance. All of the above identified features explain, to a large extent, why the 9,311, as compared to HHZ, exhibits much more vigorous early growth.