Relatives growing together: pair density and kinship

Kin selection is often used to explain the evolution altruism towards relatives through favouring the evolution of kin recognition. However, it remains unclear whether kin recognition is affected by plant pair density and different degrees of relatedness. A two-factor experimental design of kinship (three kinship degrees including siblings, closely related strangers and distantly related strangers) and pair density (including relative small, medium and large pair densities) was conducted in this study. Plant competitive traits including rosette size, specific leaf area (SLA), stem elongation, root and leaf allocation, seed biomass and vegetative biomass were measured to reflect interactions among plants living with different relatives of Arabidopsis thaliana accessions [Columbia (Col-0), Landsberg erecta (Ler) and Wassileskijia (Ws)] in three different pair densities. The SLA only showed kinship effect, and siblings showed higher SLA than non-siblings in each pair density. The plant total biomass was only affected by pair density, which increased with decreases of pair density. The rosette size, stem elongation, root allocation and leaf allocation showed interactive effects of kinship and pair density. In the large pair density, the rosette size of siblings was lower than distantly related strangers, compared to closely related strangers; the stem elongation and root allocation were lower, while the seed biomass of siblings was higher than the closely or distantly related strangers. In the medium pair density, plants living with siblings or with closely related neighbours showed higher root allocation than with distantly related neighbours. In the small pair density, the plant rosette acted similarly to of which in the large pair density, and siblings showed higher root allocation than the two strangers. The other traits in each pair density showed no significant differences among kinship treatments. A relatively large pair density achieves kin recognition by deducing root competition ability and mutual shading, with increased efficient light capture and fitness. Similar such root and efficient light capture strategies were selected in medium pair density. Except the efficient light capture strategies, small pair density also displays allocation trade-offs between roots (decreased) and leaves (increased) for siblings. Moreover, kin responses on those attributes are also adjusted by kinship degree. Thus, kinships and pair density are important variables to mediate kin interactions.     

A Plant Plasma Membrane ATP Binding Cassette–Type Transporter Is Involved in Antifungal Terpenoid Secretion

ATP binding cassette (ABC) transporters, which are found in all species, are known mainly for their ability to confer drug resistance. To date, most of the ABC transporters characterized in plants have been localized in the vacuolar membrane and are considered to be involved in the intracellular sequestration of cytotoxins. Working on the assumption that certain ABC transporters might be involved in defense metabolite secretion and their expression might be regulated by the concentration of these metabolites, we treated a Nicotiana plumbaginifolia cell culture with sclareolide, a close analog of sclareol, an antifungal diterpene produced at the leaf surface of Nicotiana spp; this resulted in the appearance of a 160-kD plasma membrane protein, which was partially sequenced. The corresponding cDNA (NpABC1) was cloned and shown to encode an ABC transporter. In vitro and in situ immunodetection showed NpABC1 to be localized in the plasma membrane. Under normal conditions, expression was found in the leaf epidermis. In cell culture and in leaf tissues, NpABC1 expression was strongly enhanced by sclareolide and sclareol. In parallel with NpABC1 induction, cells acquired the ability to excrete a labeled synthetic sclareolide derivative. These data suggest that NpABC1 is involved in the secretion of a secondary metabolite that plays a role in plant defense.     

Kin recognition in plants with distinct lifestyles: implications of biomass and nutrient niches

Kin recognition has been demonstrated by plant biomass allocation and morphology traits as well as by nitrogen (N) uptake, but has not been examined from a nutrient-niche view yet. In this study, four species with distinct lifestyles, including Glycine max (L.) Merr. (herbaceous legume), Belamcanda chinensis (L.) DC. (herbaceous non-legume), Caesalpinia pulcherrima (L.) Sw. (woody legume), and Populus tomentosa (L.) Carr. (woody non-legume) were used to demonstrate kin recognition by estimating their biomass and allocation, as well as nutrient niches based on their uptake efficiency for N, phosphorus (P), sulfur (S), potassium (K), calcium (Ca), magnesium (Mg), and iron (Fe). For G. max, kin recognition was achieved by increased biomass, and by reduced nutrient-uptake efficiency of N, P, S, K, Ca, Mg, and Fe (decreased nutrient niches) to decrease nutrient competition among kin plants compared to the strangers. Although B. chinensis and C. pulcherrima had no biomass response, kin plants of B. chinensis increased, whereas C. pulcherrima decreased their S-uptake efficiency compare to strangers. Therefore, kin competition occurred in B. chinensis through increased nutrient niche whereas kin recognition occurred in C. pulcherrima through decreased nutrient niche. By comparison, P. tomentosa showed the co-occurrence of kin recognition and competition by increased root allocation and decreased P-uptake efficiency. These findings suggest that the biomass allocation and plant nutrient niches based on their nutrient-uptake efficiency can be used as potential parameters to identify kin recognition.     

植物亲缘识别的研究进展

植物的亲缘识别(kin recognition)指植物通过识别周边个体与自己的亲缘关系, 调整自身的生长生态策略、促进亲缘个体的生存与繁衍。研究表明, 植物主要通过特定的叶片挥发物、根系分泌物、感光载体等途径, 识别周边个体与自己的亲缘关系, 改变自身形态学策略(如根系大小、根冠比、种子数量等)或者生理代谢策略(次生代谢物质、防御蛋白等), 调整与周边个体的竞争强度, 缓和与近亲缘个体之间的竞争, 加强与远亲缘或非亲缘个体的竞争。同时亲缘识别的强度也受环境因子(养分等)的影响。结合目前的研究进展, 该文分析了导致亲缘识别的研究结果存在差异或争议的主要原因, 认为主要与实验材料的选择、亲缘关系的界定标准、环境条件及测定的指标不统一有关。将来的研究应重点从生理生化、分子、代谢水平上深入研究植物亲缘识别的机理。     

Recent advance of kin recognition in plant

Plants have the ability to discriminate kin members from strangers in competitive interactions and show altruistic behavior towards related individuals. Studies have showed that plants recognize their neighbors and adjust their ecological strategy mainly through leaf volatiles, root secretions and photographic carrier. The target plants can modify their morphological traits (root size, root:shoot ratio, seed numbers etc.) or metabolism characteristics (secondary metabolites, defense-related proteins etc.) when groups of plants shared common resources, so as to minimize competition with close relatives. The density of kin recognition is influenced by environmental conditions. The main reasons for controversial experimental results of kin recognition are associated with plant materials, standard of kin selection, ecological factors and measured indices. Further studies are required to understand the mechanisms of kin interactions in plants from physiological, biochemical, molecular and metabolic levels.     

Quantitative Variation in Responses to Root Spatial Constraint within Arabidopsis thaliana

Among the myriad of environmental stimuli that plants utilize to regulate growth and development to optimize fitness are signals obtained from various sources in the rhizosphere that give an indication of the nutrient status and volume of media available. These signals include chemical signals from other plants, nutrient signals, and thigmotropic interactions that reveal the presence of obstacles to growth. Little is known about the genetics underlying the response of plants to physical constraints present within the rhizosphere. In this study, we show that there is natural variation among Arabidopsis thaliana accessions in their growth response to physical rhizosphere constraints and competition. We mapped growth quantitative trait loci that regulate a positive response of foliar growth to short physical constraints surrounding the root. This is a highly polygenic trait and, using quantitative validation studies, we showed that natural variation in EARLY FLOWERING3 (ELF3) controls the link between root constraint and altered shoot growth. This provides an entry point to study how root and shoot growth are integrated to respond to environmental stimuli.     

Characterisation of root amino acid exudation in white clover (Trifolium repens L.)

Lateral roots are crucial for the plasticity of root responses to environmental conditions in soil. The bacterivorous microfauna has been shown to increase root branching and to foster auxin producing soil bacteria. However, information on modifications of plant internal auxin content by soil bacteria and bacterivores is missing. Therefore, the effects of a rhizosphere bacterial community and a common soil amoeba (Acanthamoeba castellanii) on root branching and on auxin (indole-3-acetic acid) metabolism in Lepidium sativum and Arabidopsis thaliana were investigated. In a first experimental series, bacteria increased conjugated auxin concentrations in L. sativum shoots, but did not alter free bioactive auxin content nor root branching. In contrast, in presence of soil bacteria plus amoebae free auxin concentrations in shoots and root branching increased, demonstrating that effects of bacteria on auxin metabolism in plants were strongly modified by the bacterivorous amoebae. In a second experiment, A. thaliana reporter plants for auxin (DR5) and cytokinin (ARR5) responded similarly with increased root branching in the presence of amoebae. Surprisingly, in reporter plants cytokinin but not auxin responses were detectable, accompanied by higher soil nitrate concentrations in the presence of amoebae. Likely, increased nitrate concentrations in the rhizosphere led to an accumulation of cytokinin and interactions with free auxin in plants and finally to increased root growth in the presence of amoebae. Altogether, the results show that mutual control mechanisms exist between plant hormone metabolism and microbial signalling, and that effects on hormonal concentrations of plants by free-living bacteria are strongly influenced by bacterial grazers like amoebae.     

Kin and sex recognition in a dioecious grass

Plants have evolved complex mechanisms to recognize and respond to the presence of neighboring plants, and the genetic identity of a neighbor has been shown to make a difference in this response. Studies have found that plants are able to differentiate among self- versus non-self and among sibling (kin) competitors. Here, we present data for the dioecious grass Distichlis spicata on seedling recognition of kin and sex. D. spicata exhibits extreme spatial segregation of the sexes (SSS) in the field, and previous work has shown that intra-sexual competition is less than inter-sexual competition in the field. In this experiment, we conducted experiments in the lab, exposing the seedlings to liquid media in which seedlings had been previously grown, rather than have the seedling physically contact one another. We found that inter-sexual interactions caused a decrease in the total dry weight and an increase in root/shoot ratio of the plants compared with intra-sexual interactions. These findings suggest that D. spicata plants can recognize and respond to plant sex and that inter-sexual competition contributes to SSS, even when additional interactions, such as mycorrhizal fungi are controlled, and physical interactions between plants are removed. In the kin recognition analysis, we found that plants paired with another plant from the same mother had significantly greater lateral root number and length than plants paired with non-kin, suggesting that in this highly clonal grass, kin recognition may be an important mechanism in competitive interactions.     

New Insights into Evolution of the ABC Transporter Family in Mesostigma viride,a Unicellular Charophyte Algae

ATP-binding cassette (ABC) transporters play an important role in driving the exchange of multiple molecules across cell membranes. The plant ABC transporter family is among the largest protein families, and recent progress has advanced our understanding of ABC classification. However, the ancestral form and deep origin of plant ABCs remain elusive. In this study, we identified 59 ABC transporters in Mesostigma viride, a unicellular charophyte algae that represents the earliest diverging lineage of streptophytes, and 1034 ABCs in genomes representing a broad taxonomic sampling from distantly related plant evolutionary lineages, including chlorophytes, charophytes, bryophytes, lycophytes, gymnosperms, basal angiosperms, monocots, and eudicots. We classified the plant ABC transporters by comprehensive phylogenetic analysis of each subfamily. Our analysis revealed the ancestral type of ABC proteins as well as duplication and gene loss during plant evolution, contributing to our understanding of the functional conservation and diversity of this family. In summary, this study provides new insight into the origin and evolution of plant ABC transporters.     

GxySBA ABC Transporter of Agrobacterium tumefaciens and Its Role in Sugar Utilization and vir Gene Expression

Monosaccharides available in the extracellular milieu of Agrobacterium tumefaciens can be transported into the cytoplasm, or via the periplasmic sugar binding protein, ChvE, play a critical role in controlling virulence gene expression. The ChvE-MmsAB ABC transporter is involved in the utilization of a wide range of monosaccharide substrates but redundant transporters are likely given the ability of a chvE-mmsAB deletion strain to grow, albeit more slowly, in the presence of particular monosaccharides. In this study, a putative ABC transporter encoded by the gxySBA operon is identified and shown to be involved in the utilization of glucose, xylose, fucose, and arabinose, which are also substrates for the ChvE-MmsAB ABC transporter. Significantly, GxySBA is also shown to be the first characterized glucosamine ABC transporter. The divergently transcribed gene gxyR encodes a repressor of the gxySBA operon, the function of which can be relieved by a subset of the transported sugars, including glucose, xylose, and glucosamine, and this substrate-induced expression can be repressed by glycerol. Furthermore, deletion of the transporter can increase the sensitivity of the virulence gene expression system to certain sugars that regulate it. Collectively, the results reveal a remarkably diverse set of substrates for the GxySBA transporter and its contribution to the repression of sugar sensitivity by the virulence-controlling system, thereby facilitating the capacity of the bacterium to distinguish between the soil and plant environments.     

Whole-Genome Survey of the Putative ATP-Binding Cassette Transporter Family Genes in Vitis vinifera

The ATP-binding cassette (ABC) protein superfamily constitutes one of the largest protein families known in plants. In this report, we performed a complete inventory of ABC protein genes in Vitis vinifera, the whole genome of which has been sequenced. By comparison with ABC protein members of Arabidopsis thaliana, we identified 135 putative ABC proteins with 1 or 2 NBDs in V. vinifera. Of these, 120 encode intrinsic membrane proteins, and 15 encode proteins missing TMDs. V. vinifera ABC proteins can be divided into 13 subfamilies with 79 “full-size,” 41 “half-size,” and 15 “soluble” putative ABC proteins. The main feature of the Vitis ABC superfamily is the presence of 2 large subfamilies, ABCG (pleiotropic drug resistance and white-brown complex homolog) and ABCC (multidrug resistance-associated protein). We identified orthologs of V. vinifera putative ABC transporters in different species. This work represents the first complete inventory of ABC transporters in V. vinifera. The identification of Vitis ABC transporters and their comparative analysis with the Arabidopsis counterparts revealed a strong conservation between the 2 species. This inventory could help elucidate the biological and physiological functions of these transporters in V. vinifera.     

Chloroplast protein PLGG1 is involved in abscisic acid-regulated lateral root development and stomatal movement in Arabidopsis

The plant hormone abscisic acid (ABA) plays a crucial role in root architecture; however, the molecular mechanism of ABA-regulated lateral root (LR) growth is not well known. We screened an Arabidopsis thaliana mutant with LR growth that was sensitive to ABA from a T-DNA insertion mutant library, which was an allelic mutant of plgg1-1, termed plgg1-2. PLGG1 encodes a chloroplast protein that transports plastidic glycolate and glycerate. The length and number of LRs at the root-hypocotyl junction of plgg1-1 and plgg1-2 were significantly impaired under exogenous ABA treatment, and the transgenic plant complementary lines of plgg1-2 restored LR growth in response to ABA. In addition, we found that PLGG1 is involved in other major ABA responses, including ABA-inhibited seed germination, ABA-mediated stomatal movement, and drought tolerance. These findings open new perspectives on elucidating the mechanism of ABA response, and provide clues for analysing the functions of chloroplast proteins in regulating root growth.     

Overexpression of AtALMT1 in the Arabidopsis thaliana ecotype Columbia results in enhanced Al-activated malate excretion and beneficial bacterium recruitment

AtALMT1 (Arabidopsis thaliana ALuminum activated Malate Transporter 1) encodes an Arabidopsis thaliana malate transporter that has a pleiotropic role in Arabidopsis stress tolerance. Malate released through AtALMT1 protects the root tip from Al rhizotoxicity, and recruits beneficial rhizobacteria that induce plant immunity. To examine whether the overexpression of AtALMT1 can improve these traits, the gene, driven by the cauliflower mosaic virus 35S promoter, was introduced into the Arabidopsis ecotype Columbia. Overexpression of the gene enhanced both Al-activated malate excretion and the recruitment of beneficial bacteria Bacillus subtilis strain FB17. These findings suggest that overexpression of AtALMT1 can be used as an approach to enhance a plant's ability to release malate into the rhizosphere, which can enhance plant tolerance to some environmental stress factors.     

Grasshopper oral secretions increase salicylic acid and abscisic acid levels in wounded leaves of Arabidopsis thaliana

Recent investigations showed that the model plant Arabidopsis thaliana specifically responds to herbivory-associated molecular patterns by activating a sophisticated signaling network. The lipase activity of insect oral secretions was shown to elevate oxylipin levels when applied to puncture wounds in leaves. The results also demonstrated that the oral secretions of the generalist Schistocerca gregaria contained other, probably non-proteinous, elicitors of plant defense responses which induced mitogen-activated protein kinases, calcium signaling and ethylene levels.¹ This addendum presents data on the levels of additional phytohormones that are elevated after application of S. gregaria oral secretion to wounded leaves. Abscisic acid and salicylic acid levels are significantly elevated after elicitation with S. gregaria oral secretions, adding another layer of complexity to the herbivory-induced response of A. thaliana.Key words: abscisic acid, Arabidopsis, herbivory, salicylic acid, Schistocerca gregaria     

Mdr65 decreases toxicity of multiple insecticides in Drosophila melanogaster

ABC transporters are ubiquitous membrane-bound proteins, present in both prokaryotes and eukaryotes. The major function of eukaryotic ABC transporters is to mediate the efflux of a variety of substrates (including xenobiotics) out of cells. ABC transporters have been widely investigated in humans, particularly for their involvement in multidrug resistance (MDR). Considerably less is known about their roles in transport and/or excretion in insects. ABC transporters are only known to function as exporters in insects. Drosophila melanogaster has 56 ABC transporter genes, including eight which are phylogenetically most similar to the human Mdr genes (ABCB1 clade). We investigated the role of ABC transporters in the ABCB1 clade in modulating the susceptibility to insecticides. We took advantage of the GAL4/UAS system in D. melanogaster to knockdown the expression levels of Mdr65, Mdr50, Mdr49 and ABCB6 using transgenic UAS-RNAi lines and conditional driver lines. The most notable effects were increased sensitivities to nine different insecticides by silencing of Mdr65. Furthermore, a null mutation of Mdr65 decreased the malathion, malaoxon and fipronil LC₅₀ values by a factor of 1.9, 2.1 and 3.9, respectively. Altogether, this data demonstrates the critical role of ABC transporters, particularly Mdr65, in altering the toxicity of specific, structurally diverse, insecticides in D. melanogaster.