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The colonization of land by vascular plants is an extremely important phase in Earth’s life history. This key evolutionary process is thought to have begun during the Middle Cambrian1 period and culminated in the Silurian/Early Devonian period (interval about 509–393 million years ago (Ma)), and is documented primarily by microfossils (that is, by dispersed spores, phytodebris including fragments of algae, tissues, sporangia and cuticles), tubes and rare megafossils2 . A newly recognized fossil cooksonioid plant with in situ spores from the Barrandian area, Czech Republic, is of the highest importance because it represents extremely ancient megafossil evidence of land plant diploid generation: sporophytes (~432 Ma). The robust size of this plant places it among the largest known early polysporangiate land plants and it is probable that it attained adequate size for both aeration and effective photosynthetic competence. This would mean not only that sporophytes were photosynthetically autonomous but also that the they might have been able to sustain a relatively gametophyte-independent existence. Ancient fossil Cooksoniaplants from the Czech Republic are among the largest known early polysporangiate plants from when vascular plants were colonizing the land. They were of sufficient size to support effective photosynthesis.

The exocyst complex localizes to distinct foci at the plasma membrane of Arabidopsis thalianacells. Their localization at the plasma membrane is insensitive to BFA treatment but is decreased in an exocyst-subunit mutant. In turn, exocyst-subunit mutants show decreased exocytosis.

Activated cortical domains (ACDs) are regions of the plant cell cortex performing localized membrane turnover, delimited by concerted action of the cortical cytoskeleton and endomembrane compartments. Arabidopsis thalianarhizodermis consists of two cell types differing by a single ACD (trichoblasts, carrying tip-growing root hairs, and hairless atrichoblasts), providing a model for the study of ACD determination. We compiled a set of genes specifically upregulated in root hairs from published transcriptome data, and compared it with a “virtual Arabidopsis root hair proteome”, i.e. a list of computationally identified homologs of proteins from the published soybean root hair proteome. Both data sets were enriched in genes and proteins associated with root hairs in functional studies, but there was little overlap between the transcriptome and the proteome: the former captured gene products specific to root hairs, while the latter selected those abundant in root hairs but not necessarily specific to them. Decisive steps in ACD specification may be performed by signaling proteins of high expression specifity and low abundance. Nevertheless, 73 genes specifically transcribed in Arabidopsis trichoblasts or root hairs encode homologs of abundant root hair proteins from soybean. Most of them encode "housekeeping" proteins required for rapid tip growth. However, among the "candidates" is also a generative actin isoform, ACT11. Preliminary characterization of an act11mutant allele indeed suggests a hitherto unexpected role for this gene in root and root hair development.

The concept of plant intelligence, as proposed by Anthony Trewavas, has raised considerable discussion. However, plant intelligence remains loosely defined; often it is either perceived as practically synonymous to Darwinian fitness, or reduced to a mere decorative metaphor. A more strict view can be taken, emphasizing necessary prerequisites such as memory and learning, which requires clarifying the definition of memory itself. To qualify as memories, traces of past events have to be not only stored, but also actively accessed. We propose a criterion for eliminating false candidates of possible plant intelligence phenomena in this stricter sense: an “intelligent” behavior must involve a component that can be approximated by a plausible algorithmic model involving recourse to stored information about past states of the individual or its environment. Re-evaluation of previously presented examples of plant intelligence shows that only some of them pass our test.

Auxin (IAA) is versatile signaling molecule of plants, currently classified as plant hormone. But there are data suggesting that auxin is acting also as plant-specific morphogen, electric-responses inducing transmitter, and as general signaling molecule used for plant-bacteria communication. Our previous data revealed that auxin is associated with secretory endosomes and also highly enriched within cell walls of cells active in transcellular auxin transport. Our present data, based on in vivo non-invasive auxin flux recordings, reveal that auxin is secreted out of synaptic-like domains specialized for efflux of auxin in root apex cells highly active in polar cell-cell transport of auxin. We obtained both genetic and pharmacological evidence that phospholipase Dζ2 drives vesicular secretion of auxin for its polar transcellular transport in the transition zone of the root apex. Secretion of auxin via secretory vesicles has far-reaching consequences not only for our understanding of cell-cell auxin transport but also for plant sciences as a whole.

© 1997 Federation of European Biochemical Societies.

Rab GTPases play a central role in the control of vesicular membrane traffic. These proteins cycle between cytosolic and membrane-bound compartments in a guanine nucleotide-dependent manner, a process that is regulated by several accessory proteins. Of particular interest are the Rab guanosine nucleotide diphosphate dissociation inhibitor proteins (Rab-GDI) which bind to prenylated Rab GTPases, slow the rate of GDP dissociation and escort GDP bound Rab proteins to their target membranes and retrieve them after completion of their catalytic cycle. We have cloned from Arabidopsis thalianaa cDNA coding for the Rab guanosine diphosphate dissociation inhibitor ( AtGDI1) by functional complementation of the Saccharomyces cerevisiae sec19-1mutant. The ArabidopsiscDNA potentially encodes a 49 850 Da protein which is homologous to yeast GDI (49%) and to other members of the Rab-GDI family (49–63%). Northern blot analysis indicates that the mRNA is expressed in all tissues examined. The existence of a plant homologue of the Rab-GDI family indicates that the basic vesicle traffic control machinery may be highly conserved in plants as it is in yeast and mammals.

In a recent addendum, Oren Tzfadia and Gad Galili (PSB 2014; 9:e26732) showed that several Arabidopsisexocyst subunits possess consensus Atg8-interacting motifs (AIMs), which may mediate their interaction with the autophagy-associated Atg8 protein, providing thus a mechanistic base for participation of exocyst (sub)complexes in autophagy. However, the bioinformatically identified AIMs are short peptide motifs that may occur by chance. We thus performed an exhaustive search in a large collection of plant exocyst-derived sequences from our previous bioinformatic study and found that AIMs are over-represented among exocyst subunits of all lineages examined, including moss and club moss, compared with a representative sample of the Arabidopsisproteome. This is consistent with the proposed exocyst AIMs being biologically meaningful and evolutionarily ancient. Moreover, among the numerous EXO70 paralogs, the monocot-specific EXO70F clade appears to be exempt from the general AIM enrichment, suggesting a modification of the autophagy connection in a subset of exocyst variants.