<Emphasis Type="Italic">PAD4</Emphasis>, <Emphasis Type="Italic">LSD1</Emphasis> and <Emphasis Type="Italic">EDS1</Emphasis> regulate drought tolerance,plant biomass production,and cell wall properties

Key message

Arabidopsis and poplar with modified PAD4, LSD1 and EDS1 genes exhibit successful growth under drought stress. The acclimatory strategies depend on cell division/cell death control and altered cell wall composition.

Abstract

The increase of plant tolerance towards environmental stresses would open much opportunity for successful plant cultivation in these areas that were previously considered as ineligible, e.g. in areas with poor irrigation. In this study, we performed functional analysis of proteins encoded by PHYTOALEXIN DEFICIENT 4 (PAD4), LESION SIMULATING DISEASE 1 (LSD1) and ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1) genes to explain their role in drought tolerance and biomass production in two different species: Arabidopsis thaliana and Populus tremula × tremuloides. Arabidopsis mutants pad4-5, lsd1-1, eds1-1 and transgenic poplar lines PAD4-RNAi, LSD1-RNAi and ESD1-RNAi were examined in terms of different morphological and physiological parameters. Our experiments proved that Arabidopsis PAD4, LSD1 and EDS1 play an important role in survival under drought stress and regulate plant vegetative and generative growth. Biomass production and acclimatory strategies in poplar were also orchestrated via a genetic system of PAD4 and LSD1 which balanced the cell division and cell death processes. Furthermore, improved rate of cell division/cell differentiation and altered physical properties of poplar wood were the outcome of PAD4- and LSD1-dependent changes in cell wall structure and composition. Our results demonstrate that PAD4, LSD1 and EDS1 constitute a molecular hub, which integrates plant responses to water stress, vegetative biomass production and generative development. The applicable goal of our research was to generate transgenic plants with regulatory mechanism that perceives stress signals to optimize plant growth and biomass production in semi-stress field conditions.

     

The <Emphasis Type="Italic">Populus trichocarpa PtHSP17.8</Emphasis> involved in heat and salt stress tolerances

Key message

PtHSP17.8 was regulated by various abiotic stresses. Overexpression of PtHSP17.8 enhanced the tolerance to heat and salt stresses through maintain ROS homeostasis and cooperate with stress-related genes in Arabidopsis.

Abstract

Small heat shock proteins (sHSPs) play important roles in response to diverse biotic and abiotic stresses, especially in heat tolerance. However, limited information is available on the stress tolerance roles of sHSPs in woody species. To explore the function of sHSPs in poplar, we isolated and characterized PtHSP17.8 from Populus trichocarpa. Phylogenetic analysis and subcellular localization revealed that PtHSP17.8 was a cytosolic class I sHSP. The gene expression profile of PtHSP17.8 in various tissues showed that it was significantly accumulated in stem and root, which was consistent with the GUS expression pattern driven by promoter of PtHSP17.8. The expression of PtHSP17.8 could be induced by various abiotic stresses and significantly activated by heat stress. Overexpression of PtHSP17.8 enhanced the tolerance to heat and salt stresses in Arabidopsis. The seedling survival rate, root length, relative water content, antioxidative enzyme activities, proline, and soluble sugar content were increased in transgenic Arabidopsis under heat and salt stresses, but not in normal condition. The co-expression network of PtHSP17.8 were constructed and demonstrated many stress responsive genes included. The stress-related genes in the co-expression network were up-regulated in the PtHSP17.8 overexpression seedlings. These results suggest that PtHSP17.8 confers heat and salt tolerances in plants.

     

Endophytic microbes <Emphasis Type="Italic">Bacillus</Emphasis> sp. LZR216-regulated root development is dependent on polar auxin transport in <Emphasis Type="Italic">Arabidopsis</Emphasis> seedlings

Key message

Endophytic microbes Bacillus sp. LZR216 isolated from Arabidopsis root promoted Arabidopsis seedlings growth. It may be achieved by promoting the lateral root growth and inhibiting the primary root elongation.

Abstract

Plant roots are colonized by an immense number of microbes, including epiphytic and endophytic microbes. It was found that they have the ability to promote plant growth and protect roots from biotic and abiotic stresses. But little is known about the mechanism of the endophytic microbes-regulated root development. We isolated and identified a Bacillus sp., named as LZR216, of endophytic bacteria from Arabidopsis root. By employing a sterile experimental system, we found that LZR216 promoted the Arabidopsis seedlings growth, which may be achieved by promoting the lateral root growth and inhibiting the primary root elongation. By testing the cell type-specific developmental markers, we demonstrated that Bacillus sp. LZR216 increases the DR5::GUS and DR5::GFP expression but decreases the CYCB1;1::GUS expression in Arabidopsis root tips. Further studies indicated that LZR216 is able to inhibit the meristematic length and decrease the cell division capability but has little effect on the quiescent center function of the root meristem. Subsequently, it was also shown that LZR216 has no significant effects on the primary root length of the pin2 and aux1-7 mutants. Furthermore, LZR216 down-regulates the levels of PIN1-GFP, PIN2-GFP, PIN3-GFP, and AUX1-YFP. In addition, the wild-type Arabidopsis seedlings in the present of 1 or 5 µM NPA (an auxin transport inhibitor) were insensitive to LZR216-inhibited primary root elongation. Collectively, LZR216 regulates the development of root system architecture depending on polar auxin transport. This study shows a new insight on the ability of beneficial endophytic bacteria in regulating postembryonic root development.

     

Identification,isolation and expression analysis of eight stress-related <Emphasis Type="Italic">R2R3</Emphasis>-<Emphasis Type="Italic">MYB</Emphasis> genes in tartary buckwheat (<Emphasis Type="Italic">Fagopyrum tataricum</Emphasis>)

Key message

Eight R2R3 - MYB genes in tartary buckwheat were identified, and their expression patterns were comprehensively analyzed, which reveals role in plant response to abiotic stresses.

Abstract

The proteins of the R2R3-MYB superfamily play key roles in the growth and development processes as well as defense responses in plants. However, their characteristics and functions have not been fully investigated in tartary buckwheat (Fagopyrum tataricum), a strongly abiotic resistant coarse cereal. In this article, eight tartary buckwheat R2R3-MYB genes were isolated with full-length cDNA and DNA sequences. Phylogenetic analysis of the members of the R2R3-MYB superfamily between Arabidopsis and tartary buckwheat revealed that the assumed functions of the eight tartary buckwheat R2R3-MYB proteins are divided into five Arabidopsis functional subgroups that are involved in abiotic stress. Expression analysis during abiotic stress and exogenous phytohormone treatments identified that the eight R2R3-MYB genes responded to one or more treatments. This study is the first comprehensive analysis of the R2R3-MYB gene family in tartary buckwheat under abiotic stress.

     

Overexpression of <Emphasis Type="Italic">ThGSTZ1</Emphasis> from <Emphasis Type="Italic">Tamarix hispida</Emphasis> improves tolerance to exogenous ABA and methyl viologen

Key message

Molecular analysis of a zeta subfamily GST gene from T. hispida involved in ABA and methyl viologen tolerance in transgenic Arabidopsis and Tamarix.

Abstract

Glutathione S-transferase (GST) genes are important for the improvement of plant abiotic stress tolerance, and our previous study demonstrated that the ThGSTZ1 gene from Tamarix hispida improves plant salt and drought tolerance. To further understand the role of ThGSTZ1 in the response of plants to abscisic acid (ABA) and oxidative stress, three ThGSTZ1-overexpressing transgenic Arabidopsis thaliana lines were analyzed in the current study. The results showed that the transgenic lines exhibited higher biomass accumulation, higher activities of GST and other protective enzymes, and less reactive oxygen species (ROS) and cell damage than wild-type (WT) plants under ABA and methyl viologen (MV) stress. In addition, the analysis of a transgenic T. hispida line transiently expressing ThGSTZ1 confirmed these results. The activities of GST, glutathione peroxidase, and superoxide dismutase were markedly higher in the ThGSTZ1-overexpressing lines compared with the control lines under both ABA and MV treatments, and the transgenic lines also exhibited a lower degree of electrolyte leakage (EL) and a decreased H₂O₂ content. All these results suggested that ThGSTZ1 can also improve plant ABA and oxidation tolerance by regulating ROS metabolism and that ThGSTZ1 represents an excellent candidate gene for molecular breeding to increase plant stress tolerance.

     

Functional divergence of <Emphasis Type="Italic">GhCFE5</Emphasis> homoeologs revealed in cotton fiber and <Emphasis Type="Italic">Arabidopsis</Emphasis> root cell development

Key message

In GhCFE5 homoeologs, GhCFE5D interacted with more actin homologs and stronger interaction activity than GhCFE5A. GhCFE5D - but not GhCFE5A -overexpression severely disrupted actin cytoskeleton organization and significantly suppressed cell elongation.

Abstract

Homoeologous genes are common in polyploid plants; however, their functional divergence is poorly elucidated. Allotetraploid Upland cotton (Gossypium hirsutum, AADD) is the most widely cultivated cotton; accounting for more than 90 % of the world’s cotton production. Here, we characterized GhCFE5A and GhCFE5D homoeologs from G. hirsutum acc TM-1. GhCFE5 homoeologs are expressed preferentially in fiber cells; and a significantly greater accumulation of GhCFE5A mRNA than GhCFE5D mRNA was found in all tested tissues. Overexpression of GhCFE5D but not GhCFE5A seriously inhibits the Arabidopsis hypocotyl and root cell elongation. Yeast two-hybrid assay and bimolecular fluorescence complementation (BiFC) analysis showed that compared with GhCFE5A, GhCFE5D interacts with more actin homologs and has a stronger interaction activity both from Arabidopsis and Upland cotton. Interestingly, subcellular localization showed that GhCFE5 resides on the cortical endoplasmic reticulum (ER) network and is colocalized with actin cables. The interaction activities between GhCFE5 homoeologs and actin differ in their effects on F-actin structure in transgenic Arabidopsis root cells. The F-actin changed direction from vertical to lateral, and the actin cytoskeleton organization was severely disrupted in GhCFE5D-overexpressing root cells. These data support the functional divergence of GhCFE5 homoeologs in the actin cytoskeleton structure and cell elongation, implying an important role for GhCFE5 in the evolution and selection of cotton fiber.

     

Mechanisms of thaxtomin A-induced root toxicity revealed by a thaxtomin A sensitive <Emphasis Type="Italic">Arabidopsis</Emphasis> mutant (<Emphasis Type="Italic">ucu2</Emphasis>-<Emphasis Type="Italic">2/gi</Emphasis>-<Emphasis Type="Italic">2</Emphasis>)

Key message

The Arabidopsis mutant ( ucu2 - 2/gi - 2 ) is thaxtomin A, isoxaben and NPA-sensitive indicated by root growth and ion flux responses providing new insights into these compounds mode of action and interactions.

Abstract

Thaxtomin A (TA) is a cellulose biosynthetic inhibitor (CBI) that promotes plant cell hypertrophy and cell death. Electrophysiological analysis of steady-state K⁺ and Ca²⁺ fluxes in Arabidopsis thaliana roots pretreated with TA for 24 h indicated a disturbance in the regulation of ion movement across the plant cell membrane. The observed inability to control solute movement, recorded in rapidly growing meristematic and elongation root zones, may partly explain typical root toxicity responses to TA treatment. Of note, the TA-sensitive mutant (ucu2-2/gi-2) was more susceptible with K⁺ and Ca²⁺ fluxes altered between 1.3 and eightfold compared to the wild-type control where fluxes altered between 1.2 and threefold. Root growth inhibition assays showed that the ucu2-2/gi-2 mutant had an increased sensitivity to the auxin 2,4-D, but not IAA or NAA; it also had increased sensitivity to the auxin efflux transport inhibitor, 1-naphthylphthalamic acid (NPA), but not 2,3,5- Triiodobenzoic acid (TIBA), when compared to the WT. The NPA sensitivity data were supported by electrophysiological analysis of H⁺ fluxes in the mature (but not elongation) root zone. Increased sensitivity to the CBI, isoxaben (IXB), but not dichlobenil was recorded. Increased sensitivity to both TA and IXB corresponded with higher levels of accumulation of these toxins in the root tissue, compared to the WT. Further root growth inhibition assays showed no altered sensitivity of ucu2-2/gi-2 to two other plant pathogen toxins, alternariol and fusaric acid. Identification of a TA-sensitive Arabidopsis mutant provides further insight into how this CBI toxin interacts with plant cells.

     

Revision of the <Emphasis Type="Italic">Rhynchospora glomerata</Emphasis> species complex,focusing on the taxonomic status of <Emphasis Type="Italic">R. leptocarpa</Emphasis> (Cyperaceae)

Rhynchospora glomerata and its closest relatives comprise a group of beakesedges widespread and frequent in much of North America. The classification of the R. glomerata complex remains unresolved and controversial. The goals of this study are to determine the number of taxa in the complex and their ranks, and identify their best diagnostic characters. Measurements of eight characters from each of 101 specimens from throughout the geographic range of the complex furnished data for morphometric analyses. These analyses reveal the R. glomerata complex contains three species and no infraspecific taxa: R. capitellata, R. glomerata, and R. leptocarpa. We detected 10 validly published basionyms in the complex, five of which required lectotypification. Accordingly, we designated lectotypes for R. glomerata var. discutiens, R. glomerata var. minor, R. glomerata var. paniculata, and R. glomerata var. robustior, and the second-step lectotype for R. capitellata var. controversa.     

Update on <Emphasis Type="Italic">transparent testa</Emphasis> mutants from <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>: characterisation of new alleles from an isogenic collection

Main conclusion

We present a comprehensive overview on flavonoid-related phenotypes of A. thaliana tt and tds mutants, provide tools for their characterisation, increase the number of available alleles and demonstrate that tds3 is allelic to tt12 and tds5 to aha10.Flavonoid biosynthesis is one of the best-studied secondary metabolite pathways in plants. In the model system Arabidopsis thaliana it leads to the synthesis of three phenolic compound classes: flavonol glycosides, anthocyanins and proanthocyanidins (PAs). PAs appear brown in their oxidised polymeric forms, and most A. thaliana mutants impaired in flavonoid accumulation were identified through screens for lack of this seed coat pigmentation. These mutants are referred to as transparent testa (tt) or tannin-deficient seed (tds). More than 20 mutants of these types have been published, probably representing most of the genes relevant for PA accumulation in A. thaliana. However, data about the genes involved in PA deposition or oxidation are still rather scarce. Also, for some of the known mutants it is unclear if they represent additional loci or if they are allelic to known genes. For the present study, we have performed a systematic phenotypic characterisation of almost all available tt and tds mutants and built a collection of mutants in the genetic background of the accession Columbia to minimise effects arising from ecotype variation. We have identified a novel tt6 allele from a forward genetic screen and demonstrated that tds3 is allelic to tt12 and tds5 to aha10.

     

Combined drought and heat stress in <Emphasis Type="Italic">Camellia oleifera</Emphasis> cultivars: leaf characteristics,soluble sugar and protein contents,and Rubisco gene expression

Key message

Leaf relative water content, leaf area, leaf fresh weight, and SPAD chlorophyll meter readings along with Co - rbcL and Co - rbcS expression can be used for evaluating Camellia oleifera responses to combined drought and heat stress and subsequent recovery after rainfall events.

Abstract

Leaf characteristics, soluble protein and total soluble sugar contents as well as Rubisco-related gene expression in three cultivars of C. oleifera were measured during a combined drought and heat stress period and after subsequent rainfall events. Leaf relative water content (RWC) was significantly correlated with leaf area (LA), leaf fresh weight (FW), SPAD chlorophyll meter readings, and the levels of Co-rbcL and Co-rbcS expression. Results suggest that leaf RWC, LA, leaf FW, SPAD readings together with Co-rbcL and Co-rbcS expression can be used for evaluating responses of C. oleifera cultivars to combined drought and heat stress and subsequent recovery after rainfall events. Rubisco activase might be used for evaluating plant recovery after rainfall. This study identified cultivars differing in tolerance to the combined stress and recovery. Information derived from this study should be valuable for improving survivability and productivity of C. oleifera cultivars.