Sieve Elements Research Articles

КРИТЕРИАЛЬНАЯ ЗАВИСИМОСТЬ ДЛЯ ОПРЕДЕЛЕНИЯ УДЕЛЬНОЙ ПОВЕРХНОСТИ КОНТАКТА ФАЗ

A criterion equation is obtained for determining the specific surface of phase contact on a mass-exchange sieve plate by the method of dimensional analysis

How do fertile stamens and staminodes go differently in Kingdonia uniflora? Evidence from stamen numbers, ontogeny, and structure

Kingdonia uniflora is in Circaeasteraceae and has fertile stamens and staminodes which are both variable in number; however, the differentiating process of these two types of stamens and the nectariferous structure of staminodes are still unclear. Variation in number and ontogeny (including the degeneration stage of staminodes) of stamens in K. uniflora are investigated under SEM, TEM and LM. The results indicate that there are 63 floral formulas in 80 flowers counted, and the most frequent flower floral formula (4 flowers) is P5A°11A5G6. The correlation between the stamen number and the total floral organ number is high (0.61), while the highest correlation with the total number of floral organs is the number of carpels, and there is a weak correlation between the two types of stamens (-0.23). The stamen development period is divided into five stages, with differentiation of stamens occurring at stage 2. The anther wall formation of fertile stamens is of the basic type, and the simultaneous meiosis form tetrahedral tetrads, while mature pollens are 2-celled and tricolpate. Sporogenous tissue of staminodes fails to develop further at an earlier stage, without the formation of secondary sporogenous cells. The head of mature staminodes has nectary tissue consisting of the secretory epidermis (two types of secretory cells), nectary parenchyma (about 15 layers) and vascular tissue with vessel and sieve tube elements. There are well-developed microchannels in epidermal cell walls, and the cells related to secreting nectar are rich in mitochondria, endoplasmic reticula and small vesicles. In addition, microsporogenesis, male gametophyte development, the secretory function of staminodes, and other characteristics in K. uniflora are similar to those in Ranunculaceae. This study clarifies the differentiating stage of fertile stamens and staminodes and explores the new structure (nectary) that staminodes formed, and also, it enriched the secretion modes in Ranunculales.

玉米籽粒收获机清选装置气流场数值模拟与试验

To better analyze the distribution law of airflow in the wind sieve type cleaning device, this study took the cleaning device of Yafeng 4YZL-6S corn seed harvester as an example and conducted numerical simulation and comparative analysis of the airflow field inside the cleaning device under the sieve plate opening scales of 12, 16 and 20 mm using CFD software. The numerical simulation showed that the distribution of airflow velocity above the sieve surface was uniform at a sieve plate opening scale of 16 mm. Airflow velocity measurements were performed on the test prototype using an anemometer to verify the accuracy of the numerical simulation results. The simulation test results were supplemented by field trials, which showed that when the speed of the cleaning fan was 1200 r/min and the sieve plate opening scale was 16 mm, the impurity rate in the field harvest of the operating machinery was 1.03% and the loss rate was 1.91%. The operating effect met the standard of mechanized corn grain harvesting. This paper can provide a reference for the design and working mechanism research of corn seed harvester cleaning devices.

Seasonal Cambial Activity and Formation of Secondary Phloem and Xylem in White Oaks (Quercus alba L.)

(1) Background: the cambium has seasonal activity, forming earlywood and early phloem with relatively wide conducting cells, which will function during the most favorable season, and latewood and late phloem with narrower conducting cells, which typically function during the less favorable season. However, few studies have focused on when these two contrasting tissue types are formed in relation to climatic conditions. (2) Methods: the senior author of this paper made weekly collections for an entire year of four specimens per collection back in the 1960s, using traditional anatomical methods to study in detail what the cambium was producing progressively. (3) Results: annual growth rings are evident in both secondary xylem and secondary phloem. The cambium resumes activity in early April, with simultaneous formation of wood and secondary phloem. Both latewood and late phloem production are initiated in early June, the peak of the favorable season. The cambium ends its activity in early August. Phloem growth rings are marked by radially narrow sieve elements interspersed among a band of axial parenchyma with dark contents. Most specimens produce only one fiber band per season. This feature may be used as an indirect phloem growth ring marker. Wood growth rings are marked by very wide vessels and thick-walled, radially narrow fibers. (4) Conclusions: growth rings are evident in both secondary xylem and secondary phloem. The trees produce their latewood and late phloem long before the beginning of autumn, indicating that they prepare ahead of the selective regime, a phenomenon most likely dependent on the photoperiod. Living sieve elements are present yearlong.

Hydraulic investigations of standard and high performance trays in a DN1200 column

In the course of a more fluctuating power supply due to renewable energy sources, the need for tray columns with flexible operability increases. Accordingly, further research is required to better predict the behavior at load limits – especially for fixed and float valve trays. Within this work, the hydraulic behavior of numerous valve tray configurations was investigated employing a 1.2 m diameter gas/liquid (air/water) pilot test column. Fixed and float valve tray performance has been validated using sieve trays as a reference, which have already been extensively studied in the literature. In order to obtain significant data, weeping and entrainment limits in particular, as well as froth height and pressure drop, were measured quantitatively in the experiments. By varying the geometry parameters, numerous different cases were investigated. Based on all the data obtained, reliable statements can be made about the validity and applicability of calculation models known from the literature.

Experimental study on energy consumption characteristics of rotational–perforated static mixers

AbstractAn ideal static mixer can achieve efficient mixing at low pressure drops. Owing to the excellent performance of the tridimensional rotational flow sieve tray (TRST) in a gas–liquid two‐phase system, the TRST structure was modified into a rotational–perforated static mixer (RPSM) to enhance mixing in multicomponent liquid systems. The energy consumption characteristics of the RPSM were experimentally studied based on Reynolds numbers in the range of 986–7892, gap L = 0–80 mm, and relative angle γ = 0–45°. The effects of the element installation method, number, gap, relative angle, fluid Reynolds number, fluid properties, and other parameters on the RPSM pressure drop were also investigated. An interaction analysis of each factor was performed using the factorial design method and an empirical model of the RPSM Z‐factor was established. Additionally, pressure drop in the RPSM was compared with those of other commonly used static mixers. Results show that, when the element is backward‐installed, the pressure drop is higher than that in the forward direction because the fluid is constantly twisted. Moreover, the pressure drop increases with increasing element gap, and the average increase is 43.64% and 19.28% for the forward and backward installations, respectively. The influence of the relative angle on the pressure drop is mainly reflected when the gap L = 0. Subsequently, the degree of influence of each factor was determined, and the Z‐factor was calculated and found to be consistent with the experimental values (relative error of less than 15%).

The grapevine metabolite profile of phloem sap is modified by flavescence dorée

Flavescence dorée (FD) has been recorded in French vineyards since the mid-1950s; it has rapidly become a major threat to vineyard survival in different European grape-growing areas. Infection by the phytoplasma ‘Candidatus Phytoplasma vitis’ causes leaf chlorosis and disturbs primary and secondary core metabolic pathways; it can also occlude sieve plates, therefore affecting normal solute transport through the phloem. Thus, in the present study we hypothesised that the metabolomic fingerprint of the phloem sap changes in FDp-infected vines. The metabolome of the phloem sap collected by centrifugation from the bark of the stem of healthy and infected vines (cv. ‘Loureiro’) was profiled by ESI-HRMS at two snapshot time points: E-L 33 (grape berry still hard and green) and E-L 38 (grape berry at maturity). An untargeted analysis of the phloem sap enabled the identification of 476 metabolites, whereas the targeted analysis focused on eight main classes, namely acids, sugar and polyols, amino acids, phenolic acids, hormones, vitamins and N compounds, as well as on several minor classes like fatty acids, phenols or diols. Depending on the developmental stage of the vine, major differences were observed in the composition of cv. ‘Loureiro’ phloem sap in response to FD infection in terms of sugar, organic acid and amino acid content; furthermore, compounds involved in plant defense, such as salicylic acid, ABA, vitamin C and gallic acid also significantly changed. Overall, these results have contributed towards increasing knowledge about the complex interactions between vine and FD phytoplasma.

BIOGENIC AND ANTHROPOGENIC MAGNETIC NANOPARTICLES IN THE PHLOEM SIEVE TUBES OF PLANTS

The samples of leaves and roots of Nicotiana tabacum, the stems and tubers of Solanum tuberosum and the stems of pea Pisum sativum were examined by scanning probe microscopy in atomic force and magnetic force modes after cultivation without and with addition of magnetite nanoparticles in soil. Chains of both biogenic and anthropogenic magnetic nanoparticles are detected in the wall of the phloem sieve tubes i.e., the vascular tissue of plants. Such a localization of biogenic magnetic nanoparticles supports the idea that the chains of magnetic nanoparticles in different organs of plants have common metabolic functions. Stray gradient magnetic fields about several thousand Oe, which are created by chains of both biogenic and anthropogenic magnetic nanoparticles, can significantly affect the metabolic processes through the influence on mass transfer of vesicles, granules, organelles and other components. In view of the results of this investigation, both BMNs and anthropogenic magnetite nanoparticles chains can significantly affect the processes of mass transfer of vesicles, organelles, structural elements of the membrane and others components because they create stray magnetic fields and gradient magnetic forces.

Analysis of companion cell and phloem metabolism using a transcriptome-guided model of Arabidopsis metabolism.

Companion cells and sieve elements play an essential role in vascular plants and yet the details of the metabolism that underpins their function remain largely unknown. Here we construct a tissue-scale flux balance analysis (FBA) model to describe the metabolism of phloem loading in a mature Arabidopsis (Arabidopsis thaliana) leaf. We explore the potential metabolic interactions between mesophyll cells, companion cells, and sieve elements based on the current understanding of the physiology of phloem tissue and through the use of cell-type-specific transcriptome data as a weighting in our model. We find that companion cell chloroplasts likely play a very different role to mesophyll chloroplasts. Our model suggests that, rather than carbon capture, the most crucial function of companion cell chloroplasts is to provide photosynthetically-generated ATP to the cytosol. Additionally, our model predicts that the metabolites imported into the companion cell are not necessarily the same metabolites that are exported in phloem sap; phloem loading is more efficient if certain amino acids are synthesised in the phloem tissue. Surprisingly, in our model predictions the proton pumping pyrophosphatase (H + -PPiase) is a more efficient contributor to the energisation of the companion cell plasma membrane than the H + -ATPase. A computational model provides insight into the metabolism behind Arabidopsis phloem loading, predicting a crucial role for companion cell chloroplasts in phloem loading energy metabolism. kiad154_Supplementary_Data.zip.

Xylem development and phloem conductivity in relation to the stem mechanical strength of Paeonia lactiflora

The quality of cut Paeonia lactiflora flowers is limited by their low stem mechanical strength, but the underlying mechanism of this low strength is poorly understood. In this study, two P. lactiflora cultivars with distinct stem mechanical strengths (Chui Touhong with low stem mechanical strength and Da Fugui with high stem mechanical strength) were used as test materials. The xylem development was examined at the cellular level, and the phloem conductivity was analyzed by evaluating phloem geometry. The results showed that the secondary cell wall formation of the xylem of Chui Touhong was affected primarily in fiber cells but was affected little in vessel cells. The formation of the secondary cell walls in the xylem fiber cells of Chui Touhong was delayed, resulting in longer and thinner fiber cells with a lack of cellulose and S-lignin in the secondary cell walls. Moreover, the phloem conductivity of Chui Touhong was lower than that of Da Fugui, and more callose was accumulated in the lateral walls of the phloem sieve elements of Chui Touhong. Consequently, the delayed deposition of the secondary cell walls of the xylem fiber cells was the main factor leading to the low stem mechanical strength of Chui Touhong, and the low stem mechanical strength was closely related to the low conductivity of sieve tubes and extensive callose accumulation in the phloem. These findings provide a new perspective on enhancing P. lactiflora stem mechanical strength by targeting single cell level, and lay the foundation for future works on the correlation between phloem long-distance transport and stem mechanical strength.

Label-free superior contrast with c-band ultra-violet extinction microscopy

In 1934, Frits Zernike demonstrated that it is possible to exploit the sample’s refractive index to obtain superior contrast images of biological cells. The refractive index contrast of a cell surrounded by media yields a change in the phase and intensity of the transmitted light wave. This change can be due to either scattering or absorption caused by the sample. Most cells are transparent at visible wavelengths, which means the imaginary component of their complex refractive index, also known as extinction coefficient k, is close to zero. Here, we explore the use of c-band ultra-violet (UVC) light for high-contrast high-resolution label-free microscopy, as k is naturally substantially higher in the UVC than at visible wavelengths. Using differential phase contrast illumination and associated processing, we achieve a 7- to 300-fold improvement in contrast compared to visible-wavelength and UVA differential interference contrast microscopy or holotomography, and quantify the extinction coefficient distribution within liver sinusoidal endothelial cells. With a resolution down to 215 nm, we are, for the first time in a far-field label-free method, able to image individual fenestrations within their sieve plates which normally requires electron or fluorescence superresolution microscopy. UVC illumination also matches the excitation peak of intrinsically fluorescent proteins and amino acids and thus allows us to utilize autofluorescence as an independent imaging modality on the same setup.

Toward a Realistic Representation of Sucrose Transport in the Phloem of Plants

AbstractThe significance of phloem hydrodynamics to plant mortality and survival, which impacts ecosystem‐scale carbon and water cycling, is not in dispute. The phloem provides the conduits for products of photosynthesis to be transported to different parts of the plant for consumption or storage. The Mnch pressure flow hypothesis (PFH) is the leading framework to mathematically represent this transport. It assumes that osmosis provides the necessary pressure differences to drive water and sucrose within the phloem. Mathematical models utilizing the PFH approximate the phloem by a relatively rigid slender semi‐permeable tube. However, the phloem consists of living cells that contract and expand in response to pressure fluctuations. The effect of membrane elasticity on osmotically driven sucrose front speed has rarely been considered and frames the scope here. Laboratory experiments were conducted to elucidate the elastic‐to‐plastic pressure‐deformation relation in membranes and their effect on sucrose front speeds. It is demonstrated that membrane elasticity acts to retard the sucrose front speed. The retardation emerges because of two effects: (a) part of the osmotic pressure is diverted to perform mechanical work to expand the membrane instead of pressurizing water, and (b) expansion of the membrane reduces the sucrose concentration driving osmotic potential due to volume increases and concomitant dilution effects. These results offer a novel perspective about the much discussed presence of sieve plates throughout the phloem acting as structural expansion dampers.

Activity of Arabidopsis Rubisco small subunit promoter in various tissues of chickpea.

The activity of a green tissue-specific promoter of the Rubisco small subunit gene fromArabidopsis(AraSSU) was studied using transgenic chickpea lines. We generated transgenic chickpea lines expressing anAraSSUpromoter-drivencry2Aagene throughthe Agrobacterium-mediatedtransformation method. Lines withAraSSUexpressed the gene in all green tissues at high levels (> 90ng/mg of fresh weight tissue) compared to lines generated usingCaMV35S(< 10ng/mg FW). We used vertical cross sections of various tissues of homozygous progeny using microtome for immunolocalization. The immunolocalization showed the expression of thecry2Aagene in the green mesophyll cells of the leaves of bothAraSSUand CaMV35 chickpea lines. Moreover, the accumulation ofAraSSU-regulatedCry2Aa protein was also observed in vascular tissues, including enucleate sieve elements and their companion cells. However, no expression was observed in the roots ofAraSSUlines. In the case ofCaMV35lines, the transgene expression was observed in all the tissues. Since our data indicated that theAraSSUpromoter is active in non-green tissues such as vascular bundles. Therefore, we validated this by RT-PCR. We found Cry2Aa RNA transcripts in leaves, stems without epidermis (for vascular tissues), and roots with and without epidermis. Thus,the AraSSUpromoter is active in all above-ground tissues of the chickpea plant.

Sugars and cuticular waxes impact sugarcane aphid (Melanaphis sacchari) colonization on different developmental stages of sorghum

Sugarcane aphid (SCA; Melanaphis sacchari) is a devastating pest of sorghum (Sorghum bicolor) that colonizes sorghum plants at different growth stages. Leaf surface characteristics and sugars often influence aphid settling and feeding on host plants. However, how changes in cuticular waxes and sugar levels affect SCA establishment and feeding at different development stages of sorghum have not been explored. In this study, two- and six-week-old BTx623 plants, a reference line of sorghum, was used to evaluate plant-aphid interactions. Monitoring aphid feeding behavior using Electrical Penetration Graph (EPG) technique revealed that aphids spent more time in the sieve element phase of six-week-old plants compared to two-week-old plants. Significant differences were found in the time spent to reach the first sieve element and pathway phases between the two- and six-week-old plants. However, no-choice aphid bioassays displayed that SCA population numbers were higher in two-week-old plants compared to six-week-old plants. Differences in the abundance of wax and sugar contents were analyzed to determine how these plant components influenced aphid feeding and proliferation. Among the cuticular wax compounds analyzed, α-amyrin and isoarborinone increased after 10 days of aphid infestation only in six-week-old plants. Trehalose content was significantly increased by SCA feeding on two- and six-week-old plants. Furthermore, SCA feeding depressed sucrose content and increased levels of glucose and fructose in two-week-old but not in six-week-old plants. Overall, our study indicates that plant age is a determinant for SCA feeding, and subtle changes in triterpenoids and available sugars influence SCA establishment on sorghum plants.

Putative pectate lyase PLL12 and callose deposition through polar CALS7 are necessary for long-distance phloem transport in Arabidopsis

In plants, the phloem distributes photosynthetic products for metabolism and storage over long distances. It relies on specialized cells, the sieve elements, which are enucleated and interconnected through large so-called sieve pores in their adjoining cell walls. Reverse genetics identified PECTATE LYASE-LIKE 12 (PLL12) as critical for plant growth and development. Using genetic complementations, we established that PLL12 is required exclusively late during sieve element differentiation. Structural homology modeling, enzyme inactivation, and overexpression suggest a vital role for PLL12 in sieve-element-specific pectin remodeling. While short distance symplastic diffusion is unaffected, the pll12 mutant is unable to accommodate sustained plant development due to an incapacity to accommodate increasing hydraulic demands on phloem long-distance transport as the plant grows-a defect that is aggravated when combined with another sieve-element-specific mutant callose synthase 7 (cals7). Establishing CALS7 as a specific sieve pore marker, we investigated the subcellular dynamics of callose deposition in the developing sieve plate. Using fluorescent CALS7 then allowed identifying structural defects in pll12 sieve pores that are moderate at the cellular level but become physiologically relevant due to the serial arrangement of sieve elements in the sieve tube. Overall, pectin degradation through PLL12 appears subtle in quantitative terms. We therefore speculate that PLL12 may act as a regulator to locally remove homogalacturonan, thus potentially enabling further extracellular enzymes to access and modify the cell wall during sieve pore maturation.

Detection, Identification and Molecular Characterization of the 16SrII-V Subgroup Phytoplasma Strain Associated with Pisum sativum and Parthenium hysterophorus L.

Two unrelated plant species, green pea and parthenium weed, harboring typical phytoplasma symptoms, were discovered in Yunlin, Taiwan. Green pea (Pisum sativum.) and parthenium weed (Parthenium hysterophorus L.) are both herbaceous annual plants belonging to the Fabaceae and Asteraceae families, respectively. Displayed symptoms were witches' broom, phyllody and virescence, which are typical indications of phytoplasma infection. Pleomorphic phytoplasma-like bodies were observed under the transmission electron microscope in the sieve elements of symptomatic green pea and parthenium weed. The iPhyClassifier-based virtual RFLP study demonstrated that the phytoplasma associated with the diseased plants belongs to the 16SrII-V subgroup. The disease symptoms of both plants can be explained by the identification of PHYL1 and SAP11 effectors, identical to those of peanut witches' broom phytoplasma. The phytoplasma strains identified in this study present a very close phylogenetic relationship with other 16SrII-V subgroup phytoplasma strains discovered in Taiwan. These results not only convey the local status of the 16SrII-V subgroup phytoplasma strains but also encourage attention to be given to preventing the spread of this threat before it becomes pervasive.

Wheat–faba bean intercropping can control Fusarium wilt in faba bean under F. commune and ferulic acid stress as revealed by histopathological analysis

Fusarium wilt, is an important soilborne disease restricting the cultivation of faba bean. Wheat–faba bean intercropping is one of the useful means to control Fusarium wilt in faba bean. In this study, we analyzed the histopathological effect of wheat–faba bean intercropping system on Fusarium wilt in faba bean under F. commune and ferulic acid stress. Faba bean was inoculated with F. commune. Various concentrations of ferulic acid were added to the inoculated plants to study the occurrence of Fusarium wilt, growth of faba bean seedlings, activity of cell-wall-degrading enzymes (CWDEs) produced by F. commune in stems, and structural changes in stem tissues under monocropping and intercropping systems. When ferulic acid was added to the faba bean plants inoculated with F. commune, wheat–faba bean intercropping significantly reduced the activity of CWDEs. Microstructure observation revealed that the xylem vessel was thickened, and xylem parenchymal tissue and vascular cambium produced gelatinous substance and tylose. Moreover, callose deposition was reduced in the sieve tube; death rate of vascular tissue, cortex tissue, and epidermis tissue was reduced, and faba bean biomass was observably increased. The combination of these factors reduced the occurrence of Fusarium wilt. Therefore, wheat–faba bean intercropping reduced the severity of Fusarium wilt in faba bean by decreasing the activities of CWDEs and increasing tissue structure integrity.

The sieve-element endoplasmic reticulum: A focal point of phytoplasma-host plant interaction?

The rough endoplasmic reticulum (r-ER) is of paramount importance for adaptive responses to biotic stresses due to an increased demand for de novo synthesis of immunity-related proteins and signaling components. In nucleate cells, disturbance of r-ER integrity and functionality leads to the "unfolded protein response" (UPR), which is an important component of innate plant immune signalling. In contrast to an abundance of reports on r-ER responses to biotic challenges, sieve-element endoplasmic reticulum (SE-ER) responses to phytoplasma infection have not been investigated. We found that morphological SE-ER changes, associated with phytoplasma infection, are accompanied by differential expression of genes encoding proteins involved in shaping and anchoring the reticulum. Phytoplasma infection also triggers an increased release of bZIP signals from the (SE-ER)/r-ER and consequent differential expression of UPR-related genes. The modified expression patterns seem to reflect a trade-off between survival of host cells, needed for the phytoplasmic biotrophic lifestyle, and phytoplasmas. Specialized plasmodesmata between sieve element and companion cell may provide a corridor for transfer of phytoplasma effectors inducing UPR-related gene expression in companion cells.

First Report of 'Candidatus Phytoplasma aurantifolia' Associated with the Invasive Weed Eclipta prostrata (L.) in Taiwan.

Eclipta prostrata (L.), commonly known as false daisy of the family Asteraceae, is an erect or prostrate annual herb that grows 5 to 45 cm tall. It is widespread mainly in tropical and subtropical regions like India, China, Taiwan, Thailand, and Brazil (Chung et al., 2017). E. prostrata has very wide medicinal properties accounted by several phytochemicals like thiophene derivatives, steroids, flavonoids, and polypeptides (Feng et. al., 2019). It is also used as a traditional herbal medicine for the treatment of bleeding, hemoptysis and itching, hepatitis diarrhea, and even hair loss (Timalsina et al., 2021). In September 2021, E. prostrata displaying branch proliferation and phyllody symptoms with about 30% (6 were symptomatic and 14 were healthy) incidence rate was observed in Mailiao, Yunlin, Taiwan where phytoplasma disease is permeating and has affected many crops and non-crop species including peanut, mungbean, curl-leaved tobacco, false amaranth, etc. Compared to healthy E. prostrata bearing white ray florets and cream or dull white disk florets, symptomatic ones developed phyllody which is more pronounced on the severely infected ones. Further examination by transmission electron microscope revealed a pleomorphic (circular, elliptical, and bell-shaped) phytoplasma-like organisms accumulated in the sieve elements of the symptomatic leaves. Phytoplasma infection was further confirmed by nested polymerase chain reaction using universal primers P1/P7 (carried out for 12 cycles), followed by R16F2n/R16R2 (carried out for 35 cycles) on the genomic DNA extracted by Plant Genomic DNA Purification Kit (DP022-150, GeneMark) (Lee et al. 1993). Results revealed that the conserved 16S rRNA gene with a 1.2 kb fragment size was amplified only by the symptomatic samples. Furthermore, western blotting was done using the polyclonal antibody raised against the immunodominant membrane protein (Imp) of peanut witches'-broom (PnWB) phytoplasma, a 'Candidatus Phytoplasma aurantifolia' in Taiwan that belongs group to 16SrII (Chen et al. 2021). Consistent with the nested PCR, only the symptomatic samples revealed a specific Imp signal with a size of 19 kDa. To classify the phytoplasma associated with the symptomatic E. prostrata, the DNA sequence (No. OM397418) of the P1/P7 primer pair-amplified DNA fragment was obtained using P1 and a nested primer (5'-GGGTCTTTACTGACGCTGAGG-3'), which shares 100% identity with that of GenBank accession NZ_AMWZ01000008 (complement [31109 to 32640]) of PnWB phytoplasma. Further analysis of the virtual RFLP pattern of OM397418 by iPhyClassifier confirmed that the phytoplasma identified in the symptomatic E. prostrata belongs 16SrII-V subgroup. To the best of our knowledge, this is the first report of phytoplasma disease in E. prostrata associated with the 'Ca. P. aurantifolia' in Taiwan.

A phosphoinositide hub connects CLE peptide signaling and polar auxin efflux regulation

Auxin efflux through plasma-membrane-integral PIN-FORMED (PIN) carriers is essential for plant tissue organization and tightly regulated. For instance, a molecular rheostat critically controls PIN-mediated auxin transport in developing protophloem sieve elements of Arabidopsis roots. Plasma-membrane-association of the rheostat proteins, BREVIS RADIX (BRX) and PROTEIN KINASE ASSOCIATED WITH BRX (PAX), is reinforced by interaction with PHOSPHATIDYLINOSITOL-4-PHOSPHATE-5-KINASE (PIP5K). Genetic evidence suggests that BRX dampens autocrine signaling of CLAVATA3/EMBRYO SURROUNDING REGION-RELATED 45 (CLE45) peptide via its receptor BARELY ANY MERISTEM 3 (BAM3). How excess CLE45-BAM3 signaling interferes with protophloem development and whether it does so directly or indirectly remains unclear. Here we show that rheostat polarity is independent of PIN polarity, but interdependent with PIP5K. Catalytically inactive PIP5K confers rheostat polarity without reinforcing its localization, revealing a possible PIP5K scaffolding function. Moreover, PIP5K and PAX cooperatively control local PIN abundance. We further find that CLE45-BAM3 signaling branches via RLCK-VII/PBS1-LIKE (PBL) cytoplasmic kinases to destabilize rheostat localization. Our data thus reveal antagonism between CLE45-BAM3-PBL signaling and PIP5K that converges on auxin efflux regulation through dynamic control of PAX polarity. Because second-site bam3 mutation suppresses root as well as shoot phenotypes of pip5k mutants, CLE peptide signaling likely modulates phosphoinositide-dependent processes in various developmental contexts.