Light acclimation,retrograde signalling,cell death and immune defences in plants

This review confronts the classical view of plant immune defence and light acclimation with recently published data. Earlier findings have linked plant immune defences to nucleotide‐binding site leucine‐rich repeat (NBS‐LRR)‐dependent recognition of pathogen effectors and to the role of plasma membrane‐localized NADPH‐dependent oxidoreductase (AtRbohD), reactive oxygen species (ROS) and salicylic acid (SA). However, recent results suggest that plant immune defence also depends on the absorption of excessive light energy and photorespiration. Rapid changes in light intensity and quality often cause the absorption of energy, which is in excess of that required for photosynthesis. Such excessive light energy is considered to be a factor triggering photoinhibition and disturbance in ROS/hormonal homeostasis, which leads to cell death in foliar tissues. We highlight here the tight crosstalk between ROS‐ and SA‐dependent pathways leading to light acclimation, and defence responses leading to pathogen resistance. We also show that LESION SIMULATING DISEASE 1 (LSD1) regulates and integrates these processes. Moreover, we discuss the role of plastid–nucleus signal transduction, photorespiration, photoelectrochemical signalling and ‘light memory’ in the regulation of acclimation and immune defence responses. All of these results suggest that plants have evolved a genetic system that simultaneously regulates systemic acquired resistance (SAR), cell death and systemic acquired acclimation (SAA).     

Pathologies of non‐marine bivalve shells from the Late Triassic of Poland

Gorzelak, P., Nied?wiedzki, G. & Skawina, A. 2010: Pathologies of non‐marine bivalve shells from the Late Triassic of Poland. Lethaia, Vol. 43, pp. 285–289. Shells of Late Triassic non‐marine bivalves from Lisowice (Lipie ?l?skie clay pit, southern Poland), which co‐occur with remains of several vertebrate taxa (mammal‐like reptiles, carnivorous dinosaurs, pterosaurs, temnospondyl amphibians, hybodont sharks, dipnoan and ganoid fish), bear evidence of pathologies. Distribution, dimension and shape of some of these injuries (radiate tooth marks) closely match the dental morphology of lungfish (here probably represented by the genus Ceratodus). Thus, we interpret these pathologies as evidence of unsuccessful predatory attack on bivalves by this fish. This interpretation is also consistent with modern examples of such behaviour among lungfish. The feasibility that other culprits caused other pathologies (shell scarring and wedges) on the bivalves analysed is also discussed. Discovery of these traces constitutes important evidence of predator–prey interaction, which provides ‘fingerprints’ of trophic structure within this Late Triassic freshwater ecosystem. □Freshwater bivalves, lungfish, pathologies, predation, Triassic.     

High levels of genetic diversity in populations of Iris aphylla L. (Iridaceae), an endangered species in Poland

We used RAPDs (Random Amplified Polymorphic DNAs) to investigate genetic diversity and its partition within and between three populations of Iris aphylla in Poland. Analysis of Molecular Variance (AMOVA) of 84 distinct RAPD multiband genotypes revealed higher variation within populations (77.2%) than genetic differentiation between them (22.8%, P  < 0.002). Values of genetic diversity indices ( H ) were similar in all three sites (0.21–0.24). The differentiation of the populations corresponded to low average gene flow ( Nm  = 0.81). Our results indicated that genetic diversity was independent of population size. We concluded that although sexual reproduction and gene flow between populations of I. aphylla were very limited, they preserved high levels of genetic diversity. Relatively large number of seeds, which migrated in the past to populations, as well as patterns of reproduction and life history of I. aphylla may explain this situation.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 142 , 65–72.     

To sink or float: the fate of dormant offspring is determined by maternal behaviour in Daphnia

• 1 As the ephippia (chitinous shells enclosing diapausing eggs) of pelagic crustaceans of the genus Daphnia have been occasionally reported to float at the water surface, we considered that this might be an adaptation promoting their passive dispersal. We investigated the mechanisms by which ephippia appear at the water surface.
• 2 While field surveys revealed that floating Daphnia ephippia are often numerous in various freshwater habitats, laboratory tests showed that newly formed ephippia are not buoyant initially. Once transferred to the surface by whatever means, however, they may remain there due either to surface tension or gas absorption.
• 3 Video recordings showed that all ephippia at the water surface in laboratory vessels were shed there by ephippial females when moulting (despite the attendant risk of exposure to UV radiation). This implies that the moulting behaviour of female Daphnia may determine the fate of their dormant offspring, predetermining whether they remain in the natal environment (when the ephippium is released into the water column) or disperse (when it is deposited at the water surface).
• 4 Our findings reveal a potential mechanism underlying the high dispersal capacity of freshwater cladocerans inhabiting island‐like aquatic habitats.

     

Identification of a proline-rich Akt substrate as a 14-3-3 binding partner

Akt (also called protein kinase B) is one of the major downstream targets of the phosphatidylinositol 3-kinase pathway. This protein kinase has been implicated in insulin signaling, stimulation of cellular growth, and inhibition of apoptosis as well as transformation of cells. Although a number of cellular proteins have been identified as putative targets of the enzyme, additional substrates may play a role in the varied responses elicited by this enzyme. We have used a combination of 14-3-3 binding and recognition by an antibody to the phosphorylation consensus of the enzyme to identify and isolate one of the major substrates of Akt, which is also a 14-3-3 binding protein. This 40-kDa protein, designated PRAS40, is a proline-rich Akt substrate. Demonstration that it is a substrate of Akt was accomplished by showing that 1) PRAS40 was phosphorylated in vitro by purified Akt on the same site that was phosphorylated in insulin-treated cells; 2) activation of an inducible Akt was alone sufficient to stimulate the phosphorylation of PRAS40; and 3) cells lacking Akt1 and Akt2 exhibit a diminished ability to phosphorylate this protein. Thus, PRAS40 is a novel substrate of Akt, the phosphorylation of which leads to the binding of this protein to 14-3-3.     

Multivalent binding of PWWP2A to H2A.Z regulates mitosis and neural crest differentiation

Replacement of canonical histones with specialized histone variants promotes altering of chromatin structure and function. The essential histone variant H2A.Z affects various DNA‐based processes via poorly understood mechanisms. Here, we determine the comprehensive interactome of H2A.Z and identify PWWP2A as a novel H2A.Z‐nucleosome binder. PWWP2A is a functionally uncharacterized, vertebrate‐specific protein that binds very tightly to chromatin through a concerted multivalent binding mode. Two internal protein regions mediate H2A.Z‐specificity and nucleosome interaction, whereas the PWWP domain exhibits direct DNA binding. Genome‐wide mapping reveals that PWWP2A binds selectively to H2A.Z‐containing nucleosomes with strong preference for promoters of highly transcribed genes. In human cells, its depletion affects gene expression and impairs proliferation via a mitotic delay. While PWWP2A does not influence H2A.Z occupancy, the C‐terminal tail of H2A.Z is one important mediator to recruit PWWP2A to chromatin. Knockdown of PWWP2A in Xenopus results in severe cranial facial defects, arising from neural crest cell differentiation and migration problems. Thus, PWWP2A is a novel H2A.Z‐specific multivalent chromatin binder providing a surprising link between H2A.Z, chromosome segregation, and organ development.     

The type II isoform of bovine brain protein L-isoaspartyl methyltransferase has an endoplasmic reticulum retention signal (...RDEL) at its C-terminus.

Bovine brain is known to contain two major isoforms of protein L-isoaspartyl methyltransferase (PIMT), an enzyme that facilitates repair of atypical L-isoaspartyl peptide bonds in proteins. Although the two isoforms can be separated by anion-exchange chromatography, they appear to have similar, if not identical, substrate specificities in vitro. The more basic type I isoform has been extensively characterized, and its complete sequence has been reported. The present study was undertaken in an attempt to understand the structural and functional uniqueness of the more acidic type II isoform. Electrospray mass spectrometry of the intact enzymes revealed that the type II isoform is approximately 43 amu heavier than the type I isoform. Cyanogen bromide cleavage followed by HPLC with on-line mass analysis revealed that the type II isoform contains a unique C-terminal fragment which is 43 amu heavier than the corresponding fragment from the type I isoform. Amino acid composition analysis and direct sequencing of this fragment indicate that the type II isoform ends in the sequence ...RDEL, while the type I is known to end in ...RWK. Since ...RDEL, like ...KDEL, serves as an effective endoplasmic reticulum retention signal, we propose that the type II isoform serves to repair damaged proteins within the endoplasmic reticulum or, perhaps, within some other specialized compartment of the cell. Comparison of the protein sequences of the two bovine brain isoforms to DNA sequences for rodent PIMT reported by others suggests that the type II isoform may be produced by splicing within the codon for Arg224.     

Chilled Galleria mellonella larvae: mechanism of supernumerary moulting

ABSTRACT. Supernumerary larval instars were produced when Galleria mellonella L. (Lepidoptera) larvae were chilled at 0°C. Although sensitivity to cooling stress of the last instar and younger larvae were generally the same, only penultimate and the last instar larvae showed a significant correlation between their age and the number of additional larval moults. Chilling stress induced a rapid and persistent increase in the JH titre of the last instar larvae. Severing the ventral nerve cord resulted in a predictable loss of the ability to produce supernumerary moults in chilled last instar larvae. The data suggest that sensory input stimulates allatotropic hormone secretion by the brain of chilled larvae. The possible mechanism controlling supernumerary moulting is discussed.     

Serotonin modulates a photic response in circadian locomotor rhythmicity of adults of the blow fly, Calliphora vicina

Abstract. The present experiments were undertaken to explore a role for serotonin (5-hydroxytryptamine, 5-HT) in modulating photic signal transduction in photoreceptors of the blow fly, Calliphora vicina. Injection of p-chlorophenylalanine (pCPA) into the haemolymph appeared to reduce sensitivity to the photic effects of constant ‘bright’ light (LL hyperactivity and circadian arrhythmicity). After drug injection in bright LL, flies continued with a free-running rhythm as in constant darkness (DD) or with a lengthened period τ as in ‘dim’ LL. When 5-HT was injected into flies kept in dim LL, they became hyperactive and arrhythmic as in bright LL. This finding suggests a potential role for serotonin as mediator of circadian changes in the insect visual system including extraretinal photoreceptors.