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Seaweed extracts are a prominent class of biostimulants that enhance plant health and tolerance to biotic and abiotic stresses due to their unique bioactive components. However, the mechanisms of action of biostimulants are still unknown. Here, we have used a metabolomic approach, a UHPLC-MS method, to uncover the mechanisms induced following application to Arabidopsis thaliana of a seaweed extract derived from Durvillaea potatorum and Ascophyllum nodosum. We have identified, following the application of the extract, key metabolites and systemic responses in roots and leaves across 3 timepoints (0, 3, 5 days). Significant alterations in metabolite accumulation or reduction were found for those belonging to broad groups of compounds such as lipids, amino acids, and phytohormones; and secondary metabolites such as phenylpropanoids, glucosinolates, and organic acids. Strong accumulations of TCA cycle and N-containing and defensive metabolites such as glucosinolates were also found revealing the enhancement of carbon and nitrogen metabolism and defence systems. Our study has demonstrated that application of seaweed extract dramatically altered the metabolomic profiles of Arabidopsis and revealed differences in roots and leaves that varied across the timepoints tested. We also show clear evidence of systemic responses that were initiated in the roots and resulted in metabolic alterations in the leaves. Collectively, our results suggest that this seaweed extract promotes plant growth and activates defence systems by altering various physiological processes at the individual metabolite level. [ABSTRACT FROM AUTHOR]

Seaweed extracts are important sources of plant biostimulants that boost agricultural productivity to meet current world demand. The ability of seaweed extracts based on either of the Phaeophyceaean species Ascophyllum nodosum or Durvillaea potatorum to enhance plant growth or suppress plant disease have recently been shown. However, very limited information is available on the mechanisms of suppression of plant disease by such extracts. In addition, there is no information on the ability of a combination of extracts from A. nodosum and D. potatorum to suppress a plant pathogen or to induce plant defense. The present study has explored the transcriptome, using RNA-seq, of Arabidopsis thaliana following treatment with extracts from the two species, or a mixture of both, prior to inoculation with the root pathogen Phytophthora cinnamomi. Following inoculation, five time points (0−24 h post-inoculation) that represented early stages in the interaction of the pathogen with its host were assessed for each treatment and compared with their respective water controls. Wide scale transcriptome reprogramming occurred predominantly related to phytohormone biosynthesis and signaling, changes in metabolic processes and cell wall biosynthesis, there was a broad induction of proteolysis pathways, a respiratory burst and numerous defense-related responses were induced. The induction by each seaweed extract of defense-related genes coincident with the time of inoculation showed that the plants were primed for defense prior to infection. Each seaweed extract acted differently in inducing plant defense-related genes. However, major systemic acquired resistance (SAR)-related genes as well as salicylic acid-regulated marker genes (PR1 , PR5 , and NPR1) and auxin associated genes were found to be commonly up-regulated compared with the controls following treatment with each seaweed extract. Moreover, each seaweed extract suppressed P. cinnamomi growth within the roots of inoculated A. thaliana by the early induction of defense pathways and likely through ROS-based signaling pathways that were linked to production of ROS. Collectively, the RNA-seq transcriptome analysis revealed the induction by seaweed extracts of suites of genes that are associated with direct or indirect plant defense in addition to responses that require cellular energy to maintain plant growth during biotic stress. [ABSTRACT FROM AUTHOR]

The putative RNA helicase encoded by the Arabidopsis gene At1g32490 is a homolog of the yeast splicing RNA helicases Prp2 and Prp22. We isolated a temperature-sensitive allele ( rsw12) of the gene in a screen for root radial swelling mutants. Plants containing this allele grown at the restrictive temperature showed weak radial swelling, were stunted with reduced root elongation, and contained reduced levels of cellulose. The role of the protein was further explored by microarray analysis. By using both fold change cutoffs and a weighted gene coexpression network analysis (WGCNA) to investigate coexpression of genes, we found that the radial swelling phenotype was not linked to genes usually associated with primary cell wall biosynthesis. Instead, the mutation has strong effects on expression of secondary cell wall related genes. Many genes potentially associated with secondary walls were present in the most significant WGCNA module, as were genes coding for arabinogalactans and proteins with GPI anchors. The proportion of up-regulated genes that possess introns in rsw12 was above that expected if splicing was unrelated to the activity of the RNA helicase, suggesting that the helicase does indeed play a role in splicing in Arabidopsis. The phenotype may be due to a change in the expression of one or more genes coding for cell wall proteins. [ABSTRACT FROM AUTHOR]

Dynamin-related proteins are large GTPases that deform and cause fission of membranes. The DRP1 family of Arabidopsis thaliana has five members of which DRP1A, DRP1C, and DRP1E are widely expressed. Likely functions of DRP1A were identified by studying rsw9, a null mutant of the Columbia ecotype that grows continuously but with altered morphology. Mutant roots and hypocotyls are short and swollen, features plausibly originating in their cellulose-deficient walls. The reduction in cellulose is specific since non-cellulosic polysaccharides in rsw9 have more arabinose, xylose, and galactose than those in wild type. Cell plates in rsw9 roots lack DRP1A but still retain DRP1E. Abnormally placed and often incomplete cell walls are preceded by abnormally curved cell plates. Notwithstanding these division abnormalities, roots and stems add new cells at wild-type rates and organ elongation slows because rsw9 cells do not grow as long as wild-type cells. Absence of DRP1A reduces endocytotic uptake of FM4-64 into the cytoplasm of root cells and the hypersensitivity of elongation and radial swelling in rsw9 to the trafficking inhibitor monensin suggests that impaired endocytosis may contribute to the development of shorter fatter roots, probably by reducing cellulose synthesis. [ABSTRACT FROM PUBLISHER]

The Arabidopsis radial swelling mutant rsw10 showed ballooning of root trichoblasts, a lower than wild-type level of cellulose and altered levels of some monosaccharides in non-cellulosic polysaccharides. Map-based cloning showed that the mutated gene ( At1g71100) encodes a ribose 5-phosphate isomerase (RPI) and that the rsw10 mutation replaces a conserved glutamic acid residue with lysine. Although RPI is intimately involved with many biochemical pathways, media supplementation experiments suggest that the visible phenotype results from a defect in the production of pyrimidine-based sugar–nucleotide compounds, most likely uridine 5′-diphosphate–glucose, the presumed substrate of cellulose synthase. Two of three RPI sequences in the nuclear genome are cytoplasmic, while the third has a putative chloroplast transit sequence. The sequence encoding both cytoplasmic enzymes could complement the mutation when expressed behind the CaMV 35S promoter, while fusion of the RSW10 promoter region to the GUS reporter gene established that the gene is expressed in many aerial tissues as well as the roots. The prominence of the rsw10 phenotype in roots probably reflects RSW10 being the only cytosolic RPI in this tissue and the gene encoding the plastid RPI being relatively weakly expressed. We could not, however, detect a decrease in total RPI activity in root extracts. The rsw10 phenotype is prominent near the root tip where cells undergo division, endoreduplication and cell expansion and so are susceptible to a restriction in de novo pyrimidine production. The two cytosolic RPIs probably arose in an ancient duplication event, their present expression patterns representing subfunctionalization of the expression of the original ancestral gene. [ABSTRACT FROM AUTHOR]

Summary: rsw3 is a temperature-sensitive mutant of Arabidopsis thaliana showing radially swollen roots and a deficiency in cellulose. The rsw3 gene was identified by a map-based strategy, and shows high similarity to the catalytic α-subunits of glucosidase II from mouse, yeast and potato. These enzymes process N-linked glycans in the ER, so that they bind and then release chaperones as part of the quality control pathway, ensuring correct protein folding. Putative β-subunits for the glucosidase II holoenzyme identified in the Arabidopsis and rice genomes share characteristic motifs (including an HDEL ER-retention signal) with β-subunits in mammals and yeast. The genes encoding the putative α- and β-subunits are single copy and, like the rsw3 phenotype, widely expressed. rsw3 reduces cell number more strongly than cell size in stamen filaments and probably stems. Most features of the rsw3 phenotype are shared with other cellulose-deficient mutants, but some – notably, production of multiple rosettes and a lack of secreted seed mucilage – are not and may reflect glucosidase II affecting processes other than cellulose synthesis. The rsw3 root phenotype develops more slowly than the rsw1 and rsw2 phenotypes when seedlings are transferred to the restrictive temperature. This is consistent with rsw3 reducing glycoprotein delivery from the ER to the plasma membrane whereas rsw1 and rsw2 act more rapidly by affecting the properties of already delivered enzymes. [ABSTRACT FROM AUTHOR]

Plant priming is an induced physiological state where plants are protected from biotic and abiotic stresses. Whether seaweed extracts promote priming is largely unknown as is the mechanism by which priming may occur. In this study, we examined the effect of a seaweed extract (SWE) on two distinct stages of plant priming (priming phase and post-challenge primed state) by characterising (i) plant gene expression responses using qRT-PCR and (ii) signal transduction responses by evaluating reactive oxygen species (ROS) production. The SWE is made from the brown algae Ascophyllum nodosum and Durvillaea potatorum. The priming phase was examined using both Arabidopsis thaliana and Solanum lycopersicum. At this stage, the SWE up-regulated key priming-related genes, such as those related to systemic acquired resistance (SAR) and activated the production of ROS. These responses were found to be temporal (lasting 3 days). The post-challenge primed state was examined using A. thaliana challenged with a root pathogen. Similarly, defence response-related genes, such as PR1 and NPR1, were up-regulated and ROS production was activated (lasting 5 days). This study found that SWE induces plant priming-like responses by (i) up-regulating genes associated with plant defence responses and (ii) increasing production of ROS associated with signalling responses. [ABSTRACT FROM AUTHOR]