Climacteric and non-climacteric fruits have traditionally been viewed as representing two distinct programmes of ripening associated with differential respiration and ethylene hormone effects. In climacteric fruits, such as tomato and banana, the ripening process is marked by increased respiration and is induced and co-ordinated by ethylene, while in non-climacteric fruits, such as strawberry and grape, it is controlled by an ethylene-independent process with little change in respiration rate. The two contrasting mechanisms, however, both lead to texture, colour, and flavour changes that probably reflect some common programmes of regulatory control. It has been shown that a SEPALLATA(SEP)4-like gene is necessary for normal ripening in tomato. It has been demonstrated here that silencing a fruit-related SEP1/2-like (FaMADS9) gene in strawberry leads to the inhibition of normal development and ripening in the petal, achene, and receptacle tissues. In addition, analysis of transcriptome profiles reveals pleiotropic effects of FaMADS9 on fruit development and ripening-related gene expression. It is concluded that SEP genes play a central role in the developmental regulation of ripening in both climacteric and non-climacteric fruits. These findings provide important information to extend the molecular control of ripening in a non-climacteric fruit beyond the limited genetic and cultural options currently available.
Arabidopsis thaliana accessions are universally resistant at the adult leaf stage to white rust ( Albugo candida ) races that infect the crop species Brassica juncea and Brassica oleracea . We used transgressive segregation in recombinant inbred lines to test if this apparent species-wide (nonhost) resistance in A. thaliana is due to natural pyramiding of multiple Resistance ( R ) genes. We screened 593 inbred lines from an Arabidopsis multiparent advanced generation intercross (MAGIC) mapping population, derived from 19 resistant parental accessions, and identified two transgressive segregants that are susceptible to the pathogen. These were crossed to each MAGIC parent, and analysis of resulting F 2 progeny followed by positional cloning showed that resistance to an isolate of A. candida race 2 (Ac2V) can be explained in each accession by at least one of four genes encoding nucleotide-binding, leucine-rich repeat (NLR) immune receptors. An additional gene was identified that confers resistance to an isolate of A. candida race 9 (AcBoT) that infects B. oleracea . Thus, effector-triggered immunity conferred by distinct NLR-encoding genes in multiple A. thaliana accessions provides species-wide resistance to these crop pathogens.
Several grapevine varieties are grown in vineyards worldwide including interspecific (Vitis vinifera × Vitis spp), intraspecific (V. vinifera L. × V. vinifera L.) and inter×intraspecific (interspecific×intraspecific) hybrids with unknown origin, ambiguous naming and genetic identity. In this study, the genetic relations among eighteen grapevine hybrids and original varieties ( Vitis vinifera L.) which have mostly been described by ampelography data were analysed using AFLP (Amplified Fragments Length Polymorphism) molecular marker technology. AFLP polymorphic fragments generated by a combination of restriction digestion and PCR amplifications were assessed for analysis of the polymorphisms among accessions. Polymorphic bands were scored and genetic similarity (GS) was calculated by Dice coefficient. Cluster analysis and principle coordinate analyses (PCO) of the results addressed the genetic distance among inter-intraspecific hybrids and original grapevine varieties; detected the level of genetic similarity between varieties and specific mutant or clone; assessed the genetic relations among varieties involved in the same pedigree; recognized same genotypes under different names (synonymes) and proposed the genetic identity for an unknown, in ampelography data variety cultivated in UK vineyards.
This research studies on the evaluation of online courses are usually conducted for investigating the differences between face-to-face and Web-based environments with respect to achievement. Most of the findings indicated “no significant difference” (Russell, 1999). However, only looking at achievement as a quality measure is reducing the complex phenomena into a single variable. Therefore, an analysis of the system with its components is needed. A study on students’ frustrations with a Web-based distance education course (Hara & Kling, 1999) showed that there were two foci of frustration among students in the course. The first focus was technological problems; students without access to technical support were especially frustrated. The second focus involved the course content and the instructor’s practices in managing communications with students. Students were frustrated because of a lack of immediate feedback from the instructor and ambiguous instructions on the Web and via e-mail.
The pathosystem of Arabidopsis thaliana and diploid biotrophic oomycete Hyaloperonospora arabidopsidis (Hpa) has been a model for investigating the molecular basis of Flor's gene-for-gene hypothesis.The isolates Hpa-Noks1 and Hpa-Cala2 are virulent on Arabidopsis accession RMX-A02 whilst an F 1 generated from a cross between these two isolates was avirulent.The F 2 progeny segregated 3,1 (avirulent, virulent), indicating a single major effect AVR locus in this pathogen.SNP-based linkage mapping confirmed a single AVR locus within a 14 kb map interval containing two genes encoding putative effectors.The Hpa-Cala2 allele of one gene, designated H. arabidopsidis cryptic1 (HAC1), encodes a protein with a signal peptide and an RxLR/dEER motif, and triggers a defense response in RMX-A02.The second gene is heterozygous in Hpa-Cala2.One allele, designated Suppressor of HAC1 Cala2 (S-HAC1 Cala2 ) encodes a protein with a signal peptide and a dKEE motif with no RxLR motif; the other allele (s-hac1 Cala2 ) encodes a protein with a signal peptide, a dEEE motif and is divergent in sequence from the S-HAC1 Cala2 allele.In selfed progeny from Hpa-Cala2, dominant S-HAC1 Cala2 allele carrying progeny correlates with virulence in RMX-A02, whereas homozygous recessive s-hac1 Cala2 carrying progeny were avirulent.Genetic investigations suggested other heterozygous suppressor loci might exist in the Hpa-Cala2 genome.
Protein ids and corresponding domains of putative NLR-IDs from all plant species. Table of domain architectures detected in each protein classified as NLR-fusion. (XLSX 114 kb)
Nucleotide-binding and leucine-rich repeat receptors (NLRs) are intracellular plant immune receptors that recognize pathogen effectors secreted into the plant cell. Canonical NLRs typically contain three conserved domains including a central nucleotide binding (NB-ARC) domain, C-terminal leucine-rich repeats (LRRs) and an N-terminal domain. A subfamily of plant NLRs contain additional noncanonical domain(s) that have potentially evolved from the integration of the effector targets in the canonical NLR structure. These NLRs with extra domains are thus referred to as NLRs with integrated domains (NLR-IDs). Here, we first summarize our current understanding of NLR-ID activation upon effector binding, focusing on the NLR pairs Pik-1/Pik-2, RGA4/RGA5, and RRS1/RPS4. We speculate on their potential oligomerization into resistosomes as it was recently shown for certain canonical plant NLRs. Furthermore, we discuss how our growing understanding of the mode of action of NLR-ID continuously informs engineering approaches to design new resistance specificities in the context of rapidly evolving pathogens.
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