Summary Discovery of red‐shifted chlorophyll d and f in cyanobacteria has opened up new avenues to estimate global carbon fixation driven by far‐red light. Shaded habitats in humid subtropical forest ecosystems contain an increased proportion of far‐red light components relative to residual white light. After an extensive survey of shaded ecosystems within subtropical forests, wide occurrence of red‐shifted chlorophyll‐producing cyanobacteria was demonstrated by isolated Chl f‐producing and Chl d‐containing cyanobacteria. Chl f‐producing cyanobacteria were classified into the genera of Aphanocapsa and Chroococcidiopsis and two undescribed genera within Leptolyngbyaceae. Newly isolated Chl d‐containing Acaryochloris sp. CCNUM4 showed the closest phylogenetic relationship with Acaryochloris species isolated from marine environments. Acaryochloris sp. CCNUM4 produced Chl d as major photopigment, and Chl f‐producing cyanobacteria use Chl a under white light conditions but Chl a + f under far‐red light conditions. Their habitats are widely distributed in subtropical forest ecosystems and varied from mosses on limestone to macrophyte and freshwater in the streams and ponds. This study presents a significant advance in the knowledge of distribution and diversity of red‐shifted chlorophyll‐producing cyanobacteria in terrestrial ecosystems. The results suggest that Chl f‐producing and Chl d‐containing cyanobacteria might be important primary producers in far‐red light dominant niches worldwide.

Epac1 is a guanine nucleotide exchange factor for the small G protein Rap and is involved in membranelocalized processes such as integrin-mediated cell adhesion and cell-cell junction formation. Cyclic AMP (cAMP) directly activates Epac1 by release of autoinhibition and in addition induces its translocation to the plasma membrane. Here, we show an additional mechanism of Epac1 recruitment, mediated by activated ezrin-radixin-moesin (ERM) proteins. Epac1 directly binds with its N-terminal 49 amino acids to ERM proteins in their open conformation. Receptor-induced activation of ERM proteins results in increased binding of Epac1 and consequently the clustered localization of Epac1 at the plasma membrane. Deletion of the N terminus of Epac1, as well as disruption of the Epac1-ERM interaction by an interfering radixin mutant or small interfering RNA (siRNA)-mediated depletion of the ERM proteins, impairs Epac1-mediated cell adhesion. We conclude that ERM proteins are involved in the spatial regulation of Epac1 and cooperate with cAMPand Rap-mediated signaling to regulate adhesion to the extracellular matrix.Cyclic AMP (cAMP) is a second messenger that relays a wide range of hormone responses. The discovery of Epac as a direct effector of cAMP (15, 29) has triggered the elucidation of many cAMP-regulated processes that could not be explained by the previously known effectors protein kinase A (PKA) and cyclic nucleotide-regulated ion channels (21). Both Epac family members, Epac1 and Epac2, act as guanine nucleotide exchange factors (GEFs) for the small G proteins Rap1 and Rap2. Thereby, Epac functions in processes such as exocytosis (28,48,59), cell-cell junction formation (13,20,30,53,64), and cell-extracellular matrix (ECM) adhesion (55). Adhesion to the ECM induced by Epac1 and Rap is mediated by actin-linked integrin molecules and is implicated in diverse biological processes such as homing of endothelial progenitor cells to ischemic tissue (9), remodeling of the vasculature (10, 36), and transendothelial migration of leukocytes (37, 60).Epac1 and Epac2 are multidomain proteins containing a C-terminal catalytic region, which consists of a CDC25 homology domain responsible for GEF activity, a Ras exchange motif (REM), which stabilizes the CDC25 homology domain, and a Ras association (RA) domain. In the autoinhibited state, the catalytic site is sterically covered by the N-terminal regulatory region, which harbors a DEP (Dishevelled, Egl-10, and pleckstrin) domain and one or two cyclic nucleotide-binding domains in Epac1 and Epac2, respectively. As demonstrated by the crystal structures of both active and inactive Epac2, autoinhibition is released by a conformational change induced by the binding of cAMP (56, 57).After its production at the plasma membrane (PM) by adenylate cylases, cAMP becomes compartmentalized due to local degradation by spatially restricted phosphodiesterases (1). Further compartmentalization of cAMP signaling is established by the confined targeting of the cAMP effector proteins. Numerous adapt...

Arap3 is a phosphoinositide (PI) 3 kinase effector that serves as a GTPase activating protein (GAP) for both Arf and Rho G-proteins. The protein has multiple pleckstrin homology (PH) domains that bind preferentially phosphatidyl-inositol-3,4,5-trisphosphate (PI(3,4,5,)P 3 ) to induce translocation of Arap3 to the plasma membrane upon PI3K activation. Arap3 also contains a Ras association (RA) domain that interacts with the small G-protein Rap1 and a sterile alpha motif (SAM) domain of unknown function. In a yeast two-hybrid screen for new interaction partners of Arap3, we identified the PI 5′-phosphatase SHIP2 as an interaction partner of Arap3. The interaction between Arap3 and SHIP2 was observed with endogenous proteins and shown to be mediated by the SAM domain of Arap3 and SHIP2. In vitro, these two domains show specificity for a heterodimeric interaction. Since it was shown previously that Arap3 has a higher affinity for PI(3,4,5,)P 3 than for PI(3,4)P 2 , we propose that the SAM domain of Arap3 can function to recruit a negative regulator of PI3K signaling into the effector complex.