Differential accumulation of the mRNA of the auxin-repressed gene CsGRP1 and the auxin-induced peg formation during gravimorphogenesis of cucumber seedlings

CaARP1/CaSGT1 Module Regulates Vegetative Growth and Defense Response of Pepper Plants against Phytophthora capsici

Pepper (Capsicum annuum L.) suffers severe quality and yield loss from oomycete diseases caused by Phytophthora capsici. CaSGT1 was previously determined to positively regulate the immune response of pepper plants against P. capsici, but by which mechanism remains elusive. In the present study, the potential interacting proteins of CaSGT1 were isolated from pepper using a yeast two-hybrid system, among which CaARP1 was determined to interact with CaSGT1 via bimolecular fluorescence complementation (BiFC) and microscale thermophoresis (MST) assays. CaARP1 belongs to the auxin-repressed protein family, which is well-known to function in modulating plant growth. The transcriptional and protein levels of CaARP1 were both significantly induced by infection with P. capsici. Silencing of CaARP1 promotes the vegetative growth of pepper plants and attenuates its disease resistance to P. capsici, as well as compromising the hypersensitive response-like cell death in pepper leaves induced by PcINF1, a well-characterized typical PAMP from P. capsici. Chitin-induced transient expression of CaARP1 in pepper leaves enhanced its disease resistance to P. capsici, which is amplified by CaSGT1 co-expression as a positive regulator. Taken together, our result revealed that CaARP1 plays a dual role in the pepper, negatively regulating the vegetative growth and positively regulating plant immunity against P. capsici in a manner associated with CaSGT1.

Molecular characterization of the Brassica rapa auxin-repressed, superfamily genes, BrARP1 and BrDRM1

Two auxin-repressed superfamily genes, auxin-repressed protein 1 (ARP1) and dormancy-associated protein 1 (DRM1), are highly expressed in both the dormant buds and non-growing tissues of several plant species. To further identify the function of these proteins in Chinese cabbage (Brassica rapa L. ssp. pekinensis), we examined comprehensive expression patterns of BrARP1 and BrDRM1 under various developmental and stress conditions. We also examined these same genes in transgenic Arabidopsis plants. Both genes were expressed in all tissues tested, but their levels were highest in mature tissues accompanied by low levels of the growth-associated marker, B. rapa ribosomal protein 27. Expression of both genes was induced by abiotic stresses, such as chilling, heat shock, and salt treatment. Overexpression of either BrARP1 or BrDRM1 in Arabidopsis causes a reduction in vegetative growth and seed productivity, without affecting morphology. The lengths of petioles and siliques were greatly reduced. Simultaneous expression of both genes showed an additive effect on the growth suppression, resulting in significant reduction in plant size. Knock-out of Arabidopsis ARP1, DRM1, or both, neither affected growth rate nor final size. Results suggest BrARP1 and BrDRM1 are either involved in growth arrest, or stop growth, possibly from inhibition of either cell elongation or cell expansion, thereby creating a "growth brake".

Transcriptome analysis of resistant soybean roots infected by Meloidogyne javanica

Soybean is an important crop for Brazilian agribusiness. However, many factors can limit its production, especially root-knot nematode infection. Studies on the mechanisms employed by the resistant soybean genotypes to prevent infection by these nematodes are of great interest for breeders. For these reasons, the aim of this work is to characterize the transcriptome of soybean line PI 595099-Meloidogyne javanica interaction through expression analysis. Two cDNA libraries were obtained using a pool of RNA from PI 595099 uninfected and M. javanica (J(2)) infected roots, collected at 6, 12, 24, 48, 96, 144 and 192 h after inoculation. Around 800 ESTs (Expressed Sequence Tags) were sequenced and clustered into 195 clusters. In silico subtraction analysis identified eleven differentially expressed genes encoding putative proteins sharing amino acid sequence similarities by using BlastX: metallothionein, SLAH4 (SLAC1 Homologue 4), SLAH1 (SLAC1 Homologue 1), zinc-finger proteins, AN1-type proteins, auxin-repressed proteins, thioredoxin and nuclear transport factor 2 (NTF-2). Other genes were also found exclusively in nematode stressed soybean roots, such as NAC domain-containing proteins, MADS-box proteins, SOC1 (suppressor of overexpression of constans 1) proteins, thioredoxin-like protein 4-Coumarate-CoA ligase and the transcription factor (TF) MYBZ2. Among the genes identified in non-stressed roots only were Ser/Thr protein kinases, wound-induced basic protein, ethylene-responsive family protein, metallothionein-like protein cysteine proteinase inhibitor (cystatin) and Putative Kunitz trypsin protease inhibitor. An understanding of the roles of these differentially expressed genes will provide insights into the resistance mechanisms and candidate genes involved in soybean-M. javanica interaction and contribute to more effective control of this pathogen.

P-chlorophenoxyisobutyric acid impairs auxin response for gravity-regulated peg formation in cucumber (Cucumis sativus) seedlings

Cucumber (Cucumis sativus L.) seedlings form a specialized protuberance, the peg, on the transition zone between the hypocotyl and the root. When cucumber seeds germinate in a horizontal position, the seedlings develop a peg on the lower side of the transition zone. To verify the role of auxin action in peg formation, we examined the effect of the anti-auxin, p-chlorophenoxyisobutyric acid (PCIB), on peg formation and mRNA accumulation of auxin-regulated genes. Application of PCIB to cucumber seedlings inhibited peg formation. The application of indole-3-acetic acid (IAA) competed with PCIB and induced peg formation. Furthermore, application of PCIB decreased auxin-inducible CsIAA1 mRNA and increased auxin-repressible CsGRP1 mRNA in the lower side of the transition zone. The differential accumulation of CsIAA1 and CsGRP1 mRNAs in the transition zone of cucumber seedlings grown in a horizontal position was smaller in the PCIB-treated seedlings. These results demonstrate that endogenous auxin redistributes and induces the differential expression of auxin-regulated genes, and ultimately results in the suppression or induction of peg formation in the gravistimulated transition zone of cucumber seedlings.