The evolutionary innovation of root suberin lamellae contributed to the rise of seed plants

Functional identification of two Glycerol-3-phosphate Acyltransferase5 homologs from Chenopodium quinoa

Glycerol-3-phosphate acyltransferase5 (GPAT5) is the key enzyme in suberin biosynthesis in Arabidopsis, tomato and Sarracenia purpurea. However, little is known about whether GPAT5 function is conserved in halophytes. In this study, we identified two GPAT5 homologs, CqGPAT5a and CqGPAT5b, in Chenopodium quinoa, the typical halophyte. Using RT-qPCR, we found that CqGPAT5a and CqGPAT5b were highly expressed in quinoa roots and rapidly induced by high salt stress. CqGPAT5a and CqGPAT5b were localized to the endoplasmic reticulum and found to have glycerol-3-phosphate acyltransferase activity using yeast complementation assays. Compared with CqGPAT5b, CqGPAT5a showed relatively weaker function and less protein abundance when expressed in yeast, Arabidopsis or Nicotiana benthamiana. Subsequently, we identified a serine (S) to leucine (L) variation in the CqGPAT5a protein sequence (S251L) compared with CqGPAT5b, located in the connecting region between the second and third transmembrane domains. Site-directed mutagenesis together with yeast mutant complementation and transient expression in tobacco demonstrated that this variation significantly affected CqGPAT5a activity and protein abundance. These findings expand our understanding of GPAT5 and provide new evidence that GPAT5 may be functionally conserved in halophytes.

Exploring the function of plant root diffusion barriers in sealing and shielding for environmental adaptation

Plant roots serve as the primary interface between the plant and the soil, encountering numerous challenges ranging from water balance to nutrient uptake. One of the central mechanisms enabling plants to thrive in diverse ecosystems is the building of apoplastic diffusion barriers. These barriers control the flow of solutes into and out of the roots, maintaining water and nutrient homeostasis. In this Review, we summarize recent advances in understanding the establishment, function and ecological significance of root apoplastic diffusion barriers. We highlight the plasticity of apoplastic diffusion barriers under various abiotic stresses such as drought, salinity and nutrient deficiency. We also propose new frontiers by discussing the current bottlenecks in the study of plant apoplastic diffusion barriers.

Research Progress and Hotspots Analysis of Apoplastic Barriers in the Roots of Plants Based on Bibliometrics from 2003 to 2023

The apoplastic barriers, composed of Casparian strip (CS) and suberin lamellae (SL), are integral to the regulation of water and plant nutrient uptake in plants, as well as their resilience to abiotic stresses. This study systematically examines the research developments and emerging trends in this field from 2003 to 2023, utilizing bibliometric tools such as Web of Science, CiteSpace, and VOSviewer to analyze a dataset of 642 publications. This paper reviews the cooperation of different countries, institutions, and scholars in apoplastic barriers research based on cooperative network analysis. In the field, China has the highest number of publications, the University of Bolton has the highest number of publications, and Niko Geldner is the author with the maximum number of publications. Notably, 27 publications were identified as highly cited, with their research primarily focusing on (1) genes, proteins, enzymes, and hormones regulating the formation of apoplastic barriers; (2) the influence of adversity stress on apoplastic barriers; (3) the chemical components of apoplastic barriers; (4) the evaluations of research progress on apoplastic barriers. Combined with the keyword co-occurrence network diagram, it is proposed that future research directions in this field should be as follows: (1) physiological functions of apoplastic barriers in plant root; (2) differences in the formation of apoplastic barriers with different root systems; (3) methods to promote apoplastic barriers formation; and (4) application of molecular biology techniques. The present study provides a further understanding of the trends in apoplastic barriers, and the data analyzed can be used as a guide for future research directions.

Linking root cell wall width with plant functioning under drought conditions

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Sidhu JS, Lopez-Valdivia I, Strock CF, Schneider HM, Lynch JP. 2024. Cortical parenchyma wall width regulates root metabolic cost and maize performance under suboptimal water availability. Journal of Experimental Botany 75, https://doi.org/10.1093/jxb/erae191.

Molecular-level carbon traits underlie the multidimensional fine root economics space

Carbon influences the evolution and functioning of plants and their roots. Previous work examining a small number of commonly measured root traits has revealed a global multidimensionality of the resource economics traits in fine roots considering carbon as primary currency but without considering the diversity of carbon-related traits. To address this knowledge gap, we use data from 66 tree species from a tropical forest to illustrate that root economics space co-varies with a novel molecular-level traits space based on nuclear magnetic resonance. Thinner fine roots exhibit higher proportions of carbohydrates and lower diversity of molecular carbon than thicker roots. Mass-denser fine roots have more lignin and aromatic carbon compounds but less bioactive carbon compounds than lighter roots. Thus, the transition from thin to thick fine roots implies a shift in the root carbon economy from 'do-it-yourself' soil exploration to collaboration with mycorrhizal fungi, while the shift from light to dense fine roots emphasizes a shift from acquisitive to conservative root strategy. We reveal a previously undocumented role of molecular-level carbon traits that potentially undergird the multidimensional root economics space. This finding offers new molecular insight into the diversity of root form and function, which is fundamental to our understanding of plant evolution, species coexistence and adaptations to heterogeneous environments.

The GPAT4/6/8 clade functions in Arabidopsis root suberization nonredundantly with the GPAT5/7 clade required for suberin lamellae

Lipid polymers such as cutin and suberin strengthen the diffusion barrier properties of the cell wall in specific cell types and are essential for water relations, mineral nutrition, and stress protection in plants. Land plant-specific glycerol-3-phosphate acyltransferases (GPATs) of different clades are central players in cutin and suberin monomer biosynthesis. Here, we show that the GPAT4/6/8 clade in Arabidopsis thaliana, which is known to mediate cutin formation, is also required for developmentally regulated root suberization, in addition to the established roles of GPAT5/7 in suberization. The GPAT5/7 clade is mainly required for abscisic acid-regulated suberization. In addition, the GPAT5/7 clade is crucial for the formation of the typical lamellated suberin ultrastructure observed by transmission electron microscopy, as distinct amorphous globular polyester structures were deposited in the apoplast of the gpat5 gpat7 double mutant, in contrast to the thinner but still lamellated suberin deposition in the gpat4 gpat6 gpat8 triple mutant. Site-directed mutagenesis revealed that the intrinsic phosphatase activity of GPAT4, GPAT6, and GPAT8, which leads to monoacylglycerol biosynthesis, contributes to suberin formation. GPAT5/7 lack an active phosphatase domain and the amorphous globular polyester structure observed in the gpat5 gpat7 double mutant was partially reverted by treatment with a phosphatase inhibitor or the expression of phosphatase-dead variants of GPAT4/6/8. Thus, GPATs that lack an active phosphatase domain synthetize lysophosphatidic acids that might play a role in the formation of the lamellated structure of suberin. GPATs with active and nonactive phosphatase domains appear to have nonredundant functions and must cooperate to achieve the efficient biosynthesis of correctly structured suberin.

Suberin deficiency and its effect on the transport physiology of young poplar roots

The precise functions of suberized apoplastic barriers in root water and nutrient transport physiology have not fully been elucidated. While lots of research has been performed with mutants of Arabidopsis, little to no data are available for mutants of agricultural crop or tree species. By employing a combined set of physiological, histochemical, analytical, and transport physiological methods as well as RNA-sequencing, this study investigated the implications of remarkable CRISPR/Cas9-induced suberization defects in young roots of the economically important gray poplar. While barely affecting overall plant development, contrary to literature-based expectations significant root suberin reductions of up to 80-95% in four independent mutants were shown to not evidently affect the root hydraulic conductivity during non-stress conditions. In addition, subliminal iron deficiency symptoms and increased translocation of a photosynthesis inhibitor as well as NaCl highlight the involvement of suberin in nutrient transport physiology. The multifaceted nature of the root hydraulic conductivity does not allow drawing simplified conclusions such as that the suberin amount must always be correlated with the water transport properties of roots. However, the decreased masking of plasma membrane surface area could facilitate the uptake but also leakage of beneficial and harmful solutes.

How plants sense and respond to osmotic stress

Drought is one of the most serious abiotic stresses to land plants. Plants sense and respond to drought stress to survive under water deficiency. Scientists have studied how plants sense drought stress, or osmotic stress caused by drought, ever since Charles Darwin, and gradually obtained clues about osmotic stress sensing and signaling in plants. Osmotic stress is a physical stimulus that triggers many physiological changes at the cellular level, including changes in turgor, cell wall stiffness and integrity, membrane tension, and cell fluid volume, and plants may sense some of these stimuli and trigger downstream responses. In this review, we emphasized water potential and movements in organisms, compared putative signal inputs in cell wall-containing and cell wall-free organisms, prospected how plants sense changes in turgor, membrane tension, and cell fluid volume under osmotic stress according to advances in plants, animals, yeasts, and bacteria, summarized multilevel biochemical and physiological signal outputs, such as plasma membrane nanodomain formation, membrane water permeability, root hydrotropism, root halotropism, Casparian strip and suberin lamellae, and finally proposed a hypothesis that osmotic stress responses are likely to be a cocktail of signaling mediated by multiple osmosensors. We also discussed the core scientific questions, provided perspective about the future directions in this field, and highlighted the importance of robust and smart root systems and efficient source-sink allocations for generating future high-yield stress-resistant crops and plants.