(X.M., J.M.B., S.V.B.)Ethylene (ET) signal transduction may regulate plant growth and defense, depending on which components are recruited into the pathway in response to different stimuli. We report here that the ET pathway controls both insect resistance (IR) and plant growth enhancement (PGE) in Arabidopsis (Arabidopsis thaliana) plants responding to harpin, a protein produced by a plant pathogenic bacterium. PGE may result from spraying plant tops with harpin or by soaking seeds in harpin solution; the latter especially enhances root growth. Plants treated similarly develop resistance to the green peach aphid (Myzus persicae). The salicylic acid pathway, although activated by harpin, does not lead to PGE and IR. By contrast, PGE and IR are induced in both wild-type plants and genotypes that have defects in salicylic acid signaling. In response to harpin, levels of jasmonic acid (JA) decrease, and the COI1 gene, which is indispensable for JA signal transduction, is not expressed in wild-type plants. However, PGE and IR are stimulated in the JA-resistant mutant jar1-1. In the wild type, PGE and IR develop coincidently with increases in ET levels and the expression of several genes essential for ET signaling. The ET receptor gene ETR1 is required because both phenotypes are arrested in the etr1-1 mutant. Consistently, inhibition of ET perception nullifies the induction of both PGE and IR. The signal transducer EIN2 is required for IR, and EIN5 is required for PGE because IR and PGE are impaired correspondingly in the ein2-1 and ein5-1 mutants. Therefore, harpin activates ET signaling while conscribing EIN2 and EIN5 to confer IR and PGE, respectively. Ethylene (ET) plays important roles in plant defense (Dong, , 2001Wang et al., 2002) and in growth and development (Price et al., 2003;Guo and Ecker, 2004). Action by ET in these processes essentially depends on its perception by plants, which determines how the pathway is executed. In the absence of an ET signal, ET receptors, like ETR1 and ERS1 (Gamble et al., 2002), activate the Raf-like kinase CTR1, which in turn inhibits the downstream pathway (Clark et al., 1998). When ET is present, its binding inactivates the receptors, causing deactivation of CTR1, which allows the metal-transporter EIN2 protein (Alonso et al., 1999) or the uncharacterized component EIN5 (Roman et al., 1995) to positively regulate the pathway. Downstream, the EIN3 or ERF1 families of transcription factors may regulate the transcription of effector genes (Kieber, 1997;Chao et al., 1997). According to epistatic analysis, EIN3 and EIN5 act allelically, while EIN2 and EIN3 may act sequentially (Bleecker and Kende, 2000). EIN3 can bind to the promoter region of ERF1 (Chao et al., 1997;Solano et al., 1998). Consistently, expression of ERF genes confers constitutive ET response in ein3 backgrounds (Solano et al., 1998). Thus, EIN2 and EIN3 or EIN5 may act through ERF1 to regulate ETdependent processes (Guzmán and Ecker, 1990;Wang et al., 2002; Li et al., 2003, Traw andBergelson, 2003). However, E...

The PIN family of auxin efflux transporters exhibit polar plasma membrane (PM) localization and play a key role in auxin gradient-mediated developmental processes. Auxin inhibits PIN2 endocytosis and promotes its PM localization. However, the underlying mechanisms remain elusive. Here, we show that the inhibitory effect of auxin on PIN2 endocytosis was impaired in SCF TIR1/AFB auxin signaling mutants. Similarly, reducing membrane sterols impaired auxin inhibition of PIN2 endocytosis. Gas chromatography-mass spectrometry analyses indicate that membrane sterols were significantly reduced in SCF TIR1/AFB mutants, supporting a link between membrane sterols and auxin signaling in regulating PIN2 endocytosis. We show that auxin promoted PIN2 recycling from endosomes to the PM and increased PIN2 steady state levels in the PM fraction. Furthermore, we show that the positive effect of auxin on PIN2 levels in the PM was impaired by inhibiting membrane sterols or auxin signaling. Consistent with this, the sterol biosynthetic mutant fk-J79 exhibited pronounced defects in primary root elongation and gravitropic response. Our data collectively indicate that, although there are distinct processes involved in endocytic regulation of specific PM-resident proteins, the SCF TIR1/AFB -dependent processes are required for auxin regulation of endocytosis, recycling, and PM accumulation of the auxin efflux transporter PIN2 in Arabidopsis thaliana.

Harpin(Xoo), encoded by the hpaG(Xoo) gene of Xanthomonas oryzae pv. oryzae, is a member of the harpin group of proteins that induce pathogen resistance and hypersensitive cell death (HCD) in plants. We elaborated whether both processes are correlated in hpaG(Xoo)-expressing tobacco (HARTOB) plants, which produced harpin(Xoo) intracellularly. Resistance to fungal, bacterial, and viral pathogens increased in HARTOB, in correlation with the expression of hpaG(Xoo), the gene NPR1 that regulates several resistance pathways, and defense genes GST1, Chia5, PR-1a, and PR-1b that are mediated by different signals. However, reactive oxygen intermediate burst, the expression of HCD marker genes hsr203 and hin1, and cell death did not occur spontaneously in HARTOB, though they did in untransformed and HARTOB plants treated exogenously with harpin(Xoo). Thus, the transgenic expression of harpin(Xoo) confers nonspecific pathogen defense in the absence of HCD.

Prior research on interorganizational trust (IOT) has drawn on multiple theories across disciplines, resulting in mixed findings. This meta-analysis combines the three major theories of IOT, namely, transaction cost economics, social embeddedness theory, and resource dependence theory, to retheorize about these IOT relationships. Specifically, we consolidate 168 tests of IOT across theories and corroborate the additive predictive validity of each of the three theories and their combined explanations on IOT development. In particular, by combining IOT theories, we find an inverted U-shaped relationship between relationship duration and IOT; we also find an intertemporal link among the three IOT theories, and relationship duration as the spanning factor functions to moderate the IOT relationships across theories. These findings serve to reconcile prior conflicting findings and shed new light on IOT development. We conclude our meta-analysis by providing directions for future research.