Doil Choi and colleagues report the genome sequence of the hot pepper, Capsicum annuum, as well as the resequencing of two cultivated peppers and a wild species, Capsicum chinense. Comparative genomic analysis across Solanaceae provides insights into genome expansion, pungency, ripening and disease resistance in hot peppers.

Using mRNA differential display analysis, we isolated a salt-induced transcript that showed a significant sequence homology with an EREBP/AP2 DNA binding motif from oilseed rape plants. With this cDNA fragment as a probe, cDNA clone Tsi1 (for Tobacco stress-induced gene1) was isolated from a tobacco cDNA library. RNA gel blot analysis indicated that transcripts homologous with Tsi1 were induced not only in NaCl-treated leaves but also in leaves treated with ethephon or salicylic acid. Transient expression analysis using a Tsi1::smGFP fusion gene in BY-2 cells indicated that the Tsi1 protein was targeted to the nucleus. Fusion protein of Tsi1 with GAL4 DNA binding domain strongly activated transcription in yeast, and the transactivating activity was localized to the 13 C-terminal amino acids of Tsi1. Electrophoretic mobility shift assays revealed that Tsi1 could bind specifically to the GCC and the DRE/CRT sequences, although the binding activity to the former was stronger than that to the latter. Furthermore, Agrobacterium-mediated transient expression and transgenic plants expressing Tsi1 demonstrated that overexpression of the Tsi1 gene induced expression of several pathogenesis-related genes under normal conditions, resulting in improved tolerance to salt and pathogens. These results suggest that Tsi1 might be involved as a positive trans-acting factor in two separate signal transduction pathways under abiotic and biotic stress.

Summary: A hot pepper (Capsicum annuum) cDNA clone encoding pathogenesis‐related protein 10 (CaPR‐10) was isolated by differential screening of a cDNA library prepared from pepper leaves inoculated with tobacco mosaic virus pathotype (TMV‐P₀).CaPR‐10transcripts were induced in the incompatible interaction with TMV‐P₀orXanthomonas campestrispv.vesicatoria(Xcv) but not induced in the compatible interaction. Characterization of enzymatic properties of CaPR‐10 indicated that the recombinant protein exhibits a ribonucleolytic activity against TMV RNA, as well as against pepper total RNA, and shows its putative antiviral activity in several conditions. The CaPR‐10 protein existed at very low level in leaf tissue but was dramatically induced as soon as plants were inoculated with TMV‐P₀, and this was correlated with the increase of its ribonucleolytic activity. Immunoblot analysis and pull‐down assays using proteins extracted from pepper leaves showed that TMV‐P₀inoculation led to the phosphorylation of CaPR‐10, a modification that should affect its capacity for RNase function. We present data that the induction and subsequent phosphorylation of CaPR‐10 increased its ribonucleolytic activity to cleave invading viral RNAs, and this activity should be important to its antiviral pathway during viral attackin vivo.

Using a tobacco rattle virus (TRV)-based virus-induced gene silencing (VIGS) system, expression of phytogene desaturase (PDS) and ribulose-1,5-bisphosphate carboxylase small-subuit (rbcS) genes was suppressed in Nicotiana benthamiana and pepper plants (Capsicum annuum L. cv. Bukang). The silenced phenotypes of pale yellow (rbcS), and photobleached leaves (PDS), were invariably obvious 2 weeks after inoculation with the TRV-based vector. In a parallel experiment, the same set of genes was silenced in N. benthamiana and yielded identical phenotypes to pepper 1 week after inoculation. Northern blot analyses showed that the endogenous levels of CarbcS and CaPDS transcripts were dramatically reduced in the silenced leaf tissues. These observations confirm that the silenced phenotype is closely correlated with the pattern of tissue expression. To our knowledge, this is the first high frequency VIGS method in pepper plants. It should provide a tool for large-scale gene silencing studies in pepper functional genomics.

• Plants respond to pathogens by regulating a network of signaling pathways that fine-tune transcriptional activation of defense-related genes. • The aim of this study was to determine the role of Capsicum annuum WRKY zinc finger-domain transcription factor 1 (CaWRKY1) in defense. In previous studies, CaWRKY1 was found to be rapidly induced in C. annuum (chili pepper) leaves by incompatible and compatible pathogen inoculations, but the complexity of the network of the WRKY family prevented the function of CaWRKY1 in defense from being elucidated. • Virus-induced gene silencing of CaWRKY1 in chili pepper leaves resulted in decreased growth of Xanthomonas axonopodis pv. vesicatoria race 1. CaWRKY1-overexpressing transgenic plants showed accelerated hypersensitive cell death in response to infection with tobacco mosaic virus and Pseudomonas syringe pv. tabaci. Lower levels of pathogenesis-related gene induction were observed in CaWRKY1-overexpressing transgenic plants following salicylic acid (SA) treatments. • This work suggests that the newly characterized CaWRKY1, which is strongly induced by pathogen infections and the signal molecule SA, acts as a regulator to turn off systemic acquired resistance once the pathogen challenge has diminished and to prevent spurious activation of defense responses at suboptimal concentrations of SA.

Biocontrol offers a promising alternative to synthetic fungicides for the control of a variety of pre- and post-harvest diseases of crops. Black rot, which is caused by the pathogenic fungus Ceratocytis fimbriata, is the most destructive post-harvest disease of sweet potato, but little is currently known about potential biocontrol agents for this fungus. Here, we isolated several microorganisms from the tuberous roots and shoots of field-grown sweet potato plants, and analyzed their ribosomal RNA gene sequences. The microorganisms belonging to the genus Pantoea made up a major portion of the microbes residing within the sweet potato plants, and fluorescence microscopy showed these microbes colonized the intercellular spaces of the vascular tissue in the sweet potato stems. Four P. dispersa strains strongly inhibited C. fimbriata mycelium growth and spore germination, and altered the morphology of the fungal hyphae. The detection of dead C. fimbriata cells using Evans blue staining suggested that these P. dispersa strains have fungicidal rather than fungistatic activity. Furthermore, P. dispersa strains significantly inhibited C. fimbriata growth on the leaves and tuberous roots of a susceptible sweet potato cultivar (“Yulmi”). These findings suggest that P. dispersa strains could inhibit black rot in sweet potato plants, highlighting their potential as biocontrol agents.