Explore the vast range of titles available.

A fungal retroelement encodes a peptide that translocates into the host cytoplasm, binds a host ROP GTPase, and supports fungal virulence. This suggests neo-functionalization of repetitive DNA in Blumeria graminis. Abstract Pathogens overcome plant immunity by means of secreted effectors. Host effector targets often act in pathogen defense, but might also support fungal accommodation or nutrition. The barley ROP GTPase HvRACB is involved in accommodation of fungal haustoria of the powdery mildew fungus Blumeria graminis f.sp. hordei (Bgh) in barley epidermal cells. We found that HvRACB interacts with the ROP-interactive peptide 1 (ROPIP1) that is encoded on the active non-long terminal repeat retroelement Eg-R1 of Bgh. Overexpression of ROPIP1 in barley epidermal cells and host-induced post-transcriptional gene silencing (HIGS) of ROPIP1 suggested that ROPIP1 is involved in virulence of Bgh. Bimolecular fluorescence complementation and co-localization supported that ROPIP1 can interact with activated HvRACB in planta. We show that ROPIP1 is expressed by Bgh on barley and translocated into the cytoplasm of infected barley cells. ROPIP1 is recruited to microtubules upon co-expression of MICROTUBULE ASSOCIATED ROP GTPase ACTIVATING PROTEIN (HvMAGAP1) and can destabilize cortical microtubules. The data suggest that Bgh ROPIP targets HvRACB and manipulates host cell microtubule organization for facilitated host cell entry. This points to a possible neo-functionalization of retroelement-derived transcripts for the evolution of a pathogen virulence effector.

Pollen tubes expand by tip growth and extend directionally toward the ovule to deliver sperms during pollination. They provide an excellent model system for the study of cell polarity control and tip growth, because they grow into uniformly shaped cylindrical cells in culture. Mechanisms underlying tip growth are poorly understood in pollen tubes. It has been demonstrated that ROP1, a pollen‐specific member of the plant‐specific Rop subfamily of Rho GTPases, is a central regulator of pollen tube tip growth. Recent studies in pollen from Arabidopsis and other species have revealed a ROP‐mediated signalling network that is localized to the apical PM region of pollen tubes. The results provide evidence that the localization of this signalling network establishes the site for tip growth and the localized activation of this signalling network regulates the dynamics of tip F‐actin. These results have shown that the ROP1‐mediated dynamics of tip F‐actin is a key cellular mechanism behind tip growth in pollen tubes. Current understanding of the molecular basis for the regulation of the tip actin dynamics will be discussed.

Engulfment and Motility (ELMO) proteins are involved in the regulation of small GTPase activity in eukaryotic organisms, but little is known about ELMO proteins in plants. We isolated the barley ELMO Domain Containing Protein, HvELMOD_C, in a yeast two hybrid screen for proteins interacting with HvMAGAP1 (Microtubule Associated ROP-GTPase Activating Protein 1). HvMAGAP1 is considered as an antagonist of barley RACB, a member of the RHO of plant (ROP) family GTPases, which functions as a susceptibility factor in the interaction of barley with the barley powdery mildew fungus Blumeria graminis f.sp. hordei. HvELMOD_C interacts with the central RHO-GAP domain of HvMAGAP1. Cytoplasmic HvELMOD_C translocates to microtubules on co-expression of HvMAGAP1 but not on co-expression of HvMAGAP1-R185G, a mutant of the catalytically active arginine R185 in the RHO-GAP domain. HvELMOD_C, when simultaneously expressed with HvMAGAP1, abolished the resistance-inducing effect of HvMAGAP1 to B. graminis f.sp. hordei. Therefore, HvELMOD_C might function as a new modulator of HvMAGAP1 and thus ROP activity in barley.

BACKGROUND: The germination of both pollen and fern spores results in the emergence of a cell--pollen tube from pollen, rhizoid from spore--that grows in a polar fashion, primarily at its apical end. In both of these tip-growing cells, the delivery of secretory vesicles to the growing end is guided in part by a calcium gradient, with calcium entering at the tip where it is most highly concentrated. The similarities between the two systems extend beyond tip-focused calcium gradients to encompass signalling pathways and elements including calmodulin, nitric oxide, annexins and Rop-GTPases. SCOPE AND AIMS: This review is limited to those pathways and elements that function similarly in fern and pollen systems based on currently available evidence. The aim is to illustrate the common mechanisms by which tip growth occurs, facilitate further investigations into this area, and examine the implications for the evolutionarily conserved control of tip growth. CONCLUSIONS: The interplay of calcium, nitric oxide and other effectors in both pollen and fern spores suggests certain signalling pathways became important regulators of germination and growth early in the evolution of land plants. Both large- and small-scale comparative genomic methods have shown to be promising in their ability to find new and relevant comparisons for further research. Cross-species comparisons may serve to speed up this process by highlighting both basic pathways and system-specific deviations.