Drought and heat stress mediated activation of lipid signaling in plants: a critical review

Lipids are a principal component of plasma membrane, acting as a protective barrier between the cell and its surroundings. Abiotic stresses such as drought and temperature induce various lipid-dependent signaling responses, and the membrane lipids respond differently to environmental challenges. Recent studies have revealed that lipids serve as signal mediators forreducing stress responses in plant cells and activating defense systems. Signaling lipids, such as phosphatidic acid, phosphoinositides, sphingolipids, lysophospholipids, oxylipins, and N-acylethanolamines, are generated in response to stress. Membrane lipids are essential for maintaining the lamellar stack of chloroplasts and stabilizing chloroplast membranes under stress. However, the effects of lipid signaling targets in plants are not fully understood. This review focuses on the synthesis of various signaling lipids and their roles in abiotic stress tolerance responses, providing an essential perspective for further investigation into the interactions between plant lipids and abiotic stress

Understanding the Modus Operandi of Class II KNOX Transcription Factors in Secondary Cell Wall Biosynthesis

Lignocellulosic biomass from the secondary cell walls of plants has a veritable potential to provide some of the most appropriate raw materials for producing second-generation biofuels. Therefore, we must first understand how plants synthesize these complex secondary cell walls that consist of cellulose, hemicellulose, and lignin in order to deconstruct them later on into simple sugars to produce bioethanol via fermentation. Knotted-like homeobox (KNOX) genes encode homeodomain-containing transcription factors (TFs) that modulate various important developmental processes in plants. While Class I KNOX TF genes are mainly expressed in the shoot apical meristems of both monocot and eudicot plants and are involved in meristem maintenance and/or formation, Class II KNOX TF genes exhibit diverse expression patterns and their precise functions have mostly remained unknown, until recently. The expression patterns of Class II KNOX TF genes in Arabidopsis, namely KNAT3, KNAT4, KNAT5, and KNAT7, suggest that TFs encoded by at least some of these genes, such as KNAT7 and KNAT3, may play a significant role in secondary cell wall formation. Specifically, the expression of the KNAT7 gene is regulated by upstream TFs, such as SND1 and MYB46, while KNAT7 interacts with other cell wall proteins, such as KNAT3, MYB75, OFPs, and BLHs, to regulate secondary cell wall formation. Moreover, KNAT7 directly regulates the expression of some xylan synthesis genes. In this review, we summarize the current mechanistic understanding of the roles of Class II KNOX TFs in secondary cell wall formation. Recent success with the genetic manipulation of Class II KNOX TFs suggests that this may be one of the biotechnological strategies to improve plant feedstocks for bioethanol production

Temporal transcriptome profiling of developing seeds reveals a concerted gene regulation in relation to oil accumulation in Pongamia (Millettia pinnata)

Background Pongamia (Millettia pinnata syn. Pongamia pinnata), an oilseed legume species, is emerging as potential feedstock for sustainable biodiesel production. Breeding Pongamia for favorable traits in commercial application will rely on a comprehensive understanding of molecular mechanism regulating oil accumulation during its seed development. To date, only limited genomic or transcript sequences are available for Pongamia, while a temporal transcriptome profiling of developing seeds is still lacking in this species. Results In this work, we conducted a time-series analysis of morphological and physiological characters, oil contents and compositions, as well as global gene expression profiles in developing Pongamia seeds. Firstly, three major developmental phases were characterized based on the combined evidences from embryonic shape, seed weight, seed moisture content, and seed color. Then, the gene expression levels at these three phases were quantified by RNA-Seq analyses with three biological replicates from each phase. Nearly 94% of unigenes were expressed at all three phases, whereas only less than 2% of unigenes were exclusively expressed at one of these phases. A total of 8881 differentially expressed genes (DEGs) were identified between phases. Furthermore, the qRT-PCR analyses for 10 DEGs involved in lipid metabolism demonstrated a good reliability of our RNA-Seq data in temporal gene expression profiling. We observed a dramatic increase in seed oil content from the embryogenesis phase to the early seed-filling phase, followed by a steady and moderate increase towards the maximum at the desiccation phase. We proposed that a highly active expression of most genes related to fatty acid (FA) and triacylglycerol (TAG) biosynthesis at the embryogenesis phase might trigger both the substantial oil accumulation and the membrane lipid synthesis for rapid cell proliferation at this phase, while a concerted reactivation of TAG synthesis-related genes at the desiccation phase might further promote storage lipid synthesis to achieve the maximum content of seed oils. Conclusions This study not only built a bridge between gene expression profiles and oil accumulation in developing seeds, but also laid a foundation for future attempts on genetic engineering of Pongamia varieties to acquire higher oil yield or improved oil properties for biofuel applications

Quantification of Amu River Riverbank Erosion in Balkh Province of Afghanistan during 2004–2020

In this study, we propose quantifying the Amu River riverbank erosion with the modelled river discharge in Kaldar District, Balkh Province of Afghanistan from 2004 to 2020. We propose a framework synergizing multi-source information for modelling the erosion area based on three components: (1) river discharge, (2) river width, and (3) erosion area. The total river discharge for the watershed shared by Afghanistan and Tajikistan was modelled using hydrological parameters from the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis v5 (ERA5) data through multivariate linear regression with ground station data. The river width was determined manually using the Normalized Difference Water Index (NDWI) derived from Landsat data. The riverbank erosion area was derived from the digital shoreline analysis using the NDWI. The digital shoreline analysis showed that, between 2008 and 2020, the average riverbank erosion area in Kaldar District is about 5.4 km2 per year, and, overall, 86.3 km2 during 2004–2020 due to flood events. The significantly higher land loss events occurred at 10 km2 bank erosion during the years 2008–2009 and 2015–2016, and 19 km2 peak erosion occurred during 2011–2012. A linear relation between the erosion area with respect to the discharge intensity and the specific stream power was observed with an R2 of 0.84 and RMSE of 1.761 for both

GENETIC MODIFICATION OF LIGNOCELLULOSIC BIOMASS FOR INCREASING SACCHARIFICATION EFFICIENCY IN POPLARS

Lignin is the second most abundant biopolymer present in vascular plants. Lignification was one of the processes that allowed plants to flourish in terrestrial habitats. Lignification occurs in the secondary cell wall of tracheary elements and xylary fibers for maintaining a strong water conduction system and structural support to the plant. Apart from structural support, secondary cell walls also provide abundant, renewable and affordable biomass for production of biofuels. Genetic modification of lignocellulosic biomass present in secondary cell walls is an important strategy for improving bioethanol production. However, recalcitrance of secondary cell wall biomass hinders the release of simple sugars (saccharification) due to the complex nature of secondary cell wall. Therefore, it is necessary to understand the genetic mechanism regulating secondary cell wall biosynthesis in bioenergy plants like poplar trees. This study was performed to investigate how lignin alteration in the secondary cell walls affects wood properties influencing efficiency of saccharification. We genetically manipulated expression of phenyl-oxidase genes encoding some lignin-specific laccases and peroxidases present in the secondary cell walls driven by developing xylem-tissue specific promoter, DX15. We also genetically manipulated KNAT7 transcription factor that controls secondary cell wall formation under DX15 promoter to understand the impact of such modification on chemical properties of woody materials. Consequently, we produced hundreds of transgenic poplar plants with increased saccharification efficiency without compromising the plant growth and biomass production. Therefore, we report here some novel genetic manipulation strategies for increasing saccharification efficiency of lignocellulosic biomass in poplars

Understanding the Modus Operandi of Class II KNOX Transcription Factors in Secondary Cell Wall Biosynthesis

Lignocellulosic biomass from the secondary cell walls of plants has a veritable potential to provide some of the most appropriate raw materials for producing second-generation biofuels. Therefore, we must first understand how plants synthesize these complex secondary cell walls that consist of cellulose, hemicellulose, and lignin in order to deconstruct them later on into simple sugars to produce bioethanol via fermentation. Knotted-like homeobox (KNOX) genes encode homeodomain-containing transcription factors (TFs) that modulate various important developmental processes in plants. While Class I KNOX TF genes are mainly expressed in the shoot apical meristems of both monocot and eudicot plants and are involved in meristem maintenance and/or formation, Class II KNOXTF genes exhibit diverse expression patterns and their precise functions have mostly remained unknown, until recently. The expression patterns of Class II KNOX TF genes in Arabidopsis, namely KNAT3, KNAT4, KNAT5, and KNAT7, suggest that TFs encoded by at least some of these genes, such as KNAT7 and KNAT3, may play a significant role in secondary cell wall formation. Specifically, the expression of the KNAT7 gene is regulated by upstream TFs, such as SND1 and MYB46, while KNAT7 interacts with other cell wall proteins, such as KNAT3, MYB75, OFPs, and BLHs, to regulate secondary cell wall formation. Moreover, KNAT7 directly regulates the expression of some xylan synthesis genes. In this review, we summarize the current mechanistic understanding of the roles of Class II KNOX TFs in secondary cell wall formation. Recent success with the genetic manipulation of Class II KNOX TFs suggests that this may be one of the biotechnological strategies to improve plant feedstocks for bioethanol production

Understanding the Modus Operandi of Class II KNOX Transcription Factors in Secondary Cell Wall Biosynthesis

Lignocellulosic biomass from the secondary cell walls of plants has a veritable potential to provide some of the most appropriate raw materials for producing second-generation biofuels. Therefore, we must first understand how plants synthesize these complex secondary cell walls that consist of cellulose, hemicellulose, and lignin in order to deconstruct them later on into simple sugars to produce bioethanol via fermentation. Knotted-like homeobox (KNOX) genes encode homeodomain-containing transcription factors (TFs) that modulate various important developmental processes in plants. While Class I KNOX TF genes are mainly expressed in the shoot apical meristems of both monocot and eudicot plants and are involved in meristem maintenance and/or formation, Class II KNOX TF genes exhibit diverse expression patterns and their precise functions have mostly remained unknown, until recently. The expression patterns of Class II KNOX TF genes in Arabidopsis, namely KNAT3, KNAT4, KNAT5, and KNAT7, suggest that TFs encoded by at least some of these genes, such as KNAT7 and KNAT3, may play a significant role in secondary cell wall formation. Specifically, the expression of the KNAT7 gene is regulated by upstream TFs, such as SND1 and MYB46, while KNAT7 interacts with other cell wall proteins, such as KNAT3, MYB75, OFPs, and BLHs, to regulate secondary cell wall formation. Moreover, KNAT7 directly regulates the expression of some xylan synthesis genes. In this review, we summarize the current mechanistic understanding of the roles of Class II KNOX TFs in secondary cell wall formation. Recent success with the genetic manipulation of Class II KNOX TFs suggests that this may be one of the biotechnological strategies to improve plant feedstocks for bioethanol production

Drought and heat stress mediated activation of lipid signaling in plants: a critical review

Lipids are a principal component of plasma membrane, acting as a protective barrier between the cell and its surroundings. Abiotic stresses such as drought and temperature induce various lipid-dependent signaling responses, and the membrane lipids respond differently to environmental challenges. Recent studies have revealed that lipids serve as signal mediators forreducing stress responses in plant cells and activating defense systems. Signaling lipids, such as phosphatidic acid, phosphoinositides, sphingolipids, lysophospholipids, oxylipins, and N-acylethanolamines, are generated in response to stress. Membrane lipids are essential for maintaining the lamellar stack of chloroplasts and stabilizing chloroplast membranes under stress. However, the effects of lipid signaling targets in plants are not fully understood. This review focuses on the synthesis of various signaling lipids and their roles in abiotic stress tolerance responses, providing an essential perspective for further investigation into the interactions between plant lipids and abiotic stress

Genetic Modification of KNAT7 Transcription Factor Expression Enhances Saccharification and Reduces Recalcitrance of Woody Biomass in Poplars

The precise role of KNAT7 transcription factors (TFs) in regulating secondary cell wall (SCW) biosynthesis in poplars has remained unknown, while our understanding of KNAT7 functions in other plants is continuously evolving. To study the impact of genetic modifications of homologous and heterologous KNAT7 gene expression on SCW formation in transgenic poplars, we prepared poplar KNAT7 (PtKNAT7) overexpression (PtKNAT7-OE) and antisense suppression (PtKNAT7-AS) vector constructs for the generation of transgenic poplar lines via Agrobacterium-mediated transformation. Since the overexpression of homologous genes can sometimes result in co-suppression, we also overexpressed Arabidopsis KNAT7 (AtKNAT7-OE) in transgenic poplars. In all these constructs, the expression of KNAT7 transgenes was driven by developing xylem (DX)-specific promoter, DX15. Compared to wild-type (WT) controls, many SCW biosynthesis genes downstream of KNAT7 were highly expressed in poplar PtKNAT7-OE and AtKNAT7-OE lines. Yet, no significant increase in lignin content of woody biomass of these transgenic lines was observed. PtKNAT7-AS lines, however, showed reduced expression of many SCW biosynthesis genes downstream of KNAT7 accompanied by a reduction in lignin content of wood compared to WT controls. Syringyl to Guaiacyl lignin (S/G) ratios were significantly increased in all three KNAT7 knockdown and overexpression transgenic lines than WT controls. These transgenic lines were essentially indistinguishable from WT controls in terms of their growth phenotype. Saccharification efficiency of woody biomass was significantly increased in all transgenic lines than WT controls. Overall, our results demonstrated that developing xylem-specific alteration of KNAT7 expression affects the expression of SCW biosynthesis genes, impacting at least the lignification process and improving saccharification efficiency, hence providing one of the powerful tools for improving bioethanol production from woody biomass of bioenergy crops and trees

Putrescine Mitigates High Temperature Effects by Modulating Morpho-Physiological and Biochemical Attributes in Brassica juncea Seedlings

A variety of environmental issues are affecting crops all across the world, but rising temperatures are posing the greatest threat. High temperature has been found to drastically inhibit seedling emergence and cause leaf necrosis at the seedling stage, which results in poor plant stand and significantly decreased yields. Polyamines (PAs) are positively charged, low-molecular-weight aliphatic nitrogenous bases present in all living organisms and are involved in various biological processes in plant growth and development, including senescence and response to different abiotic stresses. Putrescine (Put) functions as a master growth regulator that promotes optimal plant development and greater stress tolerance. Here, the current study aimed to elucidate how Put (1 mM) functions in reducing the negative impacts of high temperature on four varieties of Brassica juncea (RH-1707, RH-1708, RH-1566 and RH-1999-42). Exposure of plants to high temperature resulted in decrease in growth parameters, chlorophyll content and relative water content. Simultaneously, increases were found in antioxidant enzymes, electrolyte leakage, lipid peroxidation, hydrogen peroxide content and stomatal density. High temperature more significantly affected varieties RH-1707 and RH-1708, while RH-1566 and RH-1999-42 showed lesser effects. Exogenous application of Put mitigated the negative impacts of high temperature by enhancing growth, chlorophyll content, relative water content and antioxidant enzyme activities and, simultaneously, it reduces oxidative damage and stomatal density. This study specifies that varieties RH-1707 and RH-1708 are sensitive whereas RH-1566 and RH-1999-42 are tolerant of high temperature and provides an insight into the effectiveness of Put in mitigating the effects of high temperature to a significant extent in B. juncea seedlings