New insights into the functional roles of CrRLKs in the control of plant cell growth and development

Receptor-like kinases (RLKs) are a family of transmembrane proteins with a variable ligand-binding extracellular domain and a cytoplasmic kinase domain. In Arabidopsis, there are ∼600 RLKs believed to have diverse functions during plant growth, development and interactions with the environment. Based on the variable extracellular domain, RLKs can be classified into different subfamilies. The CrRLK subfamily contains 17 members in Arabidopsis and characterization of some of its members suggests a role for these proteins in the regulation of growth and reproduction. This review focuses on the roles of CrRLKs in the regulation of polarized growth with emphasis on the newly identified signal transduction pathways activated downstream of CrRLKs. A picture is emerging where CrRLKs are part of a conserved signal transduction cascade important for growth maintenance in different cell types.Key words: CrRLKs, FERONIA, RAC/ROP, ROS, polar growthThe ability of plants to perceive and process environmental and internal information into coordinated responses is crucial to their adaptability and survival in constantly changing environments. Most of signal perception occurs at the plasma membrane of cells where membrane-associated receptors receive signals to activate downstream signaling cascades that regulate growth and development. In plants and animals alike, receptor-like kinases (RLKs) mediate many of the signaling events at the cell surface and in the model plant Arabidopsis they comprise a monophyletic family with more than 600 members.¹ RLKs are transmembrane proteins with a variable N-terminal extracellular domain and a Ser/Thr intracellular kinase domain. The diversity of their extracellular domains suggests involvement in the transduction of a wide range of signals and allows them to be classified into different sub-families.² The CrRLK1L subfamily (from here on referred to as CrRLK) is named after the first member characterized in Catharanthus roseus cell cultures³ and contains 17 members in Arabidopsis.⁴ Several members of this family have now been implicated in growth regulatory processes.THESEUS1 (THE1) was identified through a suppressor screen of a cellulose-deficient mutant (prc1-1) which has a short hypocotyl phenotype.⁵ Loss of THE1 function resulted in reduced growth inhibition in the prc1-1 the1 double mutant. Interestingly, the the1 mutation itself has no effect in wild type background, thus leading to the suggestion that THE1 functions as a sensor of cell wall integrity in situations where the cell wall is weakened and organ elongation would be detrimental for the plant.^4,5A second CrRLK, FERONIA (FER), was first implicated in the regulation of female control of fertility. In the female gametophyte FER is involved in sensing pollen tube arrival and promoting its rupture which is necessary for double fertilization to occur.^6,7 FER is in fact involved in several processes depending on the tissue where it is expressed. In hypocotyls, FER is involved in the integration of ethylene and brassinosteroid (BR) signals to regulate hypocotyl elongation in the dark.⁸ Moreover, FER, THE1 and the closely related HERCULES1 (HERK1), were found to regulate cell elongation by interacting with BR signaling.⁹ More recently, roles for FER in the regulation of root hair development and fungal invasion have been established.^10,11 The pollen-specific ANXUR1 (ANX1) and ANXUR2 (ANX2) are closely related to FER and act redundantly to maintain pollen tube growth integrity during its journey through the style and ensure against precocious pollen tube rupture before reaching the ovule.^12,13Apparently with different biological roles, all the CrRLK members analyzed thus far have an effect on the growth of plant cells. The present review focuses on their role during cell growth with emphasis on polar cell growth and the downstream pathways activated by CrRLKs.     

The oligodeoxynucleotide sequences corresponding to never-expressed peptide motifs are mainly located in the non-coding strand

Background  

We study the usage of specific peptide platforms in protein composition. Using the pentapeptide as a unit of length, we find that in the universal proteome many pentapeptides are heavily repeated (even thousands of times), whereas some are quite rare, and a small number do not appear at all. To understand the physico-chemical-biological basis underlying peptide usage at the proteomic level, in this study we analyse the energetic costs for the synthesis of rare and never-expressed versus frequent pentapeptides. In addition, we explore residue bulkiness, hydrophobicity, and codon number as factors able to modulate specific peptide frequencies. Then, the possible influence of amino acid composition is investigated in zero- and high-frequency pentapeptide sets by analysing the frequencies of the corresponding inverse-sequence pentapeptides. As a final step, we analyse the pentadecamer oligodeoxynucleotide sequences corresponding to the never-expressed pentapeptides.     

Proteomic analysis of somatic embryogenesis in <Emphasis Type="Italic">Vitis vinifera</Emphasis>

Two dimensional gel electrophoresis coupled to mass spectrometry has been used to study the somatic embryogenesis in Vitis vinifera, by comparing embryogenic and non embryogenic calluses of the Thompson seedless cv. More than 1,000 spots were reproducibly resolved in colloidal Coomassie brilliant blue stained gels over a pI nonlinear range of 3–10 in the first dimension and using homogeneous 12.5% polyacrylamide gels in the second dimension. The expression pattern of 35 spots differed significantly between the two samples. These spots were processed by mass spectrometry analysis and the protein identity was assigned by using both the non-redundant protein and EST databases. Several responsive proteins, some already known to be involved in the somatic embryogenesis process while others, for the first time put into relation with this process, have been described. Moreover, they have been subdivided in functional categories, and their putative role is discussed in terms of their relevance in the somatic embryogenesis process.     

Thirty polymorphic microsatellite loci from the critically endangered kakapo (Strigops habroptilus)

Thirty polymorphic microsatellite loci were developed from the critically endangered kakapo (Strigops habroptilus), using an enriched genomic library. Characterization of loci using 90 kakapo revealed an average of 3.3 alleles per locus (range: 2–5) and an average expected heterozygosity of 0.47 (range: 0.17–0.70). The probability of identity (7.2 × 10^?15) and probability of exclusion (0.999999) demonstrate that these loci are a highly informative marker set that can aid the genetic management of the kakapo.     

The Serratia-type hemolysin of Chromobacterium violaceum

Chromobacterium violaceum is a Gram-negative opportunistic human pathogen and an inhabitant of tropical soils and waterways. Although known primarily for the synthesis of the pigment violacein, and more recently as a reporter strain for quorum sensing, clinical reports of chromobacteriosis comprise the largest block of published literature on this organism. Genome sequencing has revealed many potential virulence factors in this microorganism, and this paper establishes the presence in C. violaceum of a Serratia type-hemolysin (ChlA) and transporter (ChlB). We also show that the hemolysin operon includes a third gene (chlC) that is predicted to encode a phosphorylation domain similar to the receiver domain of response regulators in bacterial signal transduction systems.     

Use of a disposable water filter for prevention of false-positive results due to nontuberculosis mycobacteria in a clinical laboratory performing routine acid-fast staining for tuberculosis

A point-of-use 0.2-microm filter was evaluated for elimination of nontuberculosis mycobacteria in laboratory water to reduce false-positive acid-fast bacillus staining results. Use of the point-of-use filter can significantly reduce the false-positive rate to 1.2% compared to samples treated with tap water (10.7%) and deionized water (8.7%).     

Spatial–Temporal Variation in Orchid Bee Communities (Hymenoptera: Apidae) in Remnants of Arboreal Caatinga in the Chapada Diamantina Region, State of Bahia, Brazil

The spatial and temporal distribution of organisms is a fundamental aspect of biological communities. The present study focused on three remnants of arboreal Caatinga in northeastern Brazil between May, 2009 and April, 2010. A total of 627 euglossine males were captured in traps baited with artificial aromatic compounds. The specimens belonged to 14 species and four genera: Euglossa Latreille, Eulaema Lepeletier, Eufriesea Cockerell, and Exaerete Hoffmannsegg. Eulaema nigrita Lepeletier (41.6), Euglossa carolina Nemésio (15.3%), Eulaema marcii Nemésio (13.6%), and Euglossa melanotricha Moure (12.8%) were the most common species sampled. The distribution of collected specimens per fragment was as follows: Braúna (280?ha)??259 individuals belonging to 14 species; Cambuí (179?ha)??161 individuals from eight species; and Pindoba (100?ha)??207 individuals represented by seven species. Braúna had the highest diversity (H???=?1.91) and estimated species richness. The largest fragment was the main source of the observed variation in species richness and abundance, indicating a non-random pattern of spatial distribution. The analysis of environmental factors indicated that seasonal variation in these factors was the principal determinant of species occurrence and abundance.     

Rapid loss of phosphorus from dying ryegrass roots: the chemical components involved

Summary Lolium perenne was grown in solution culture with either ample or deficient phosphate supply (high-P and low-P plants). The concentration in the roots of phosphorus as water-soluble compounds, phospholipid and insoluble residue was measured. A supplementary experiment showed that the concentration of each component in the roots of low-P plants was similar to that in plants grown in P-deficient soil. The time-course of the decline of each P component was determined in roots detached from the shoot and left hanging in solution. During the three weeks residue P concentration in the roots declined little. In contrast, both types of root lost about three-quarters of their lipid P in the first week. Low-P roots lost little of their water-soluble P. High-P roots contained much more water-soluble P and lost much of it during the first two weeks. By the end of three weeks their water-soluble P content was levelling out at a value similar to that in low-P roots, suggesting a non-labile pool. The rapid loss of lipid P from low-P roots comprised more than half of their total loss, and the possible ecological significance of this is discussed.     

Cycling of nutrients from dying roots to living plants,including the role of mycorrhizas

This paper presents information about the release of nitrogen and phosphorus from dying grass roots and the capture of phosphorus by other, living plants. We have paid particular attention to the part played by mycorrhizas in this phosphorus capture, and the possible importance of mycorrhizal links between dying and living roots.WhenLolium perenne plants were grown with ample nutrients and their roots then detached and buried in soil, about half the nitrogen and two-thirds of the phosphorus was lost in three weeks, but only one-fifth of the dry weight. The C:N and C:P ratios suggest that microbial growth in the roots would at first be C-limited but would become N- and P-limited within three weeks.Rapid transfer of³²P can occur from dying roots to those of a living plant if the two root systems are intermingled. The amount transferred was substantially increased in two species-combinations that are known to form mycorrhizal links between their root systems. In contrast, in a species-combination where only the living (receiver) plant could become mycorrhizal no significant increase of³²P transfer occurred. This evidence, although far from conclusive, suggests that mycorrhizal links between dying and living roots can contribute to nutrient cycling. This research indicates a major difference in nutrient cycling processes between perennial and annual crops.