Zhendong Tian

Novel potato C2H2-type zinc finger protein gene, StZFP1, which responds to biotic and abiotic stress, plays a role in salt tolerance.

Many TFIIIA-type zinc finger proteins (ZFPs) play important roles in stress responses in plants. In the present study, a novel zinc finger protein gene, StZFP1, was cloned from potato. StZFP1 is a typical TFIIIA-type two-finger zinc finger gene with one B-box domain, one L-box domain and a DLN-box/EAR motif. The StZFP1 genes belong to a small gene family with an estimated copy number of four or five, located on chromosome I. StZFP1 is constitutively expressed in leaves, stems, roots, tubers and flowers of adult plants. Expression of StZFP1 can be induced by salt, dehydration and exogenously applied ABA. StZFP1 expression is also responsive to infection by the late blight pathogen Phytophthora infestans. Transient expression analysis of StZFP1:GFP fusion protein revealed that StZFP1 is preferentially localised in the nucleus. Ectopic expression of StZFP1, driven by the Arabidopsis rd29A promoter in transgenic tobacco, increased plant tolerance to salt stress. These results demonstrate that StZFP1 might be involved in potato responses to salt and dehydration stresses through an ABA-dependent pathway.

A Phytophthora infestans RXLR effector targets plant PP1c isoforms that promote late blight disease

Plant pathogens deliver effectors to alter host processes. Knowledge of how effectors target and manipulate host proteins is critical to understand crop disease. Here, we show that in planta expression of the RXLR effector Pi04314 enhances leaf colonization by Phytophthora infestans via activity in the host nucleus and attenuates induction of jasmonic and salicylic acid-responsive genes. Pi04314 interacts with three host protein phosphatase 1 catalytic (PP1c) isoforms, causing their re-localization from the nucleolus to the nucleoplasm. Re-localization of PP1c-1 also occurs during infection and is dependent on an R/KVxF motif in the effector. Silencing the PP1c isoforms or overexpression of a phosphatase-dead PP1c-1 mutant attenuates infection, demonstrating that host PP1c activity is required for disease. Moreover, expression of PP1c–1mut abolishes enhanced leaf colonization mediated by in planta Pi04314 expression. We argue that PP1c isoforms are susceptibility factors forming holoenzymes with Pi04314 to promote late blight disease.

U-box E3 ubiquitin ligase PUB17 acts in the nucleus to promote specific immune pathways triggered by Phytophthora infestans

Highlight Ubiquitin E3 ligase PUB17 functions in the nucleus to regulate transcriptional responses positively in PAMP-triggered immunity and programmed cell death following perception of specific elicitors at the plant cell surface.

Cloning and molecular characterization of the potato RING finger protein gene StRFP1 and its function in potato broad-spectrum resistance against Phytophthora infestans

Really interesting new gene (RING) finger proteins function as ubiquitin ligase and play key roles in biotic and abiotic stresses. A new RING-H2 finger protein gene, StRFP1, was cloned from Phytophthora infestans-inoculated leaves of potato (Solanum tuberosum) clone 386209.10, which is free of R1-R11 genes. The deduced amino acid sequence was characterized by an N-terminal transmembrane domain, a GLD region and a RING-H2 finger signature. StRFP1 is homologous to the tobacco NtACRE132 protein and belongs to the ATL family. The DNA gel blot analysis and mapping revealed that StRFP1, an intron-free gene, had one to two copies in the potato genome and was located on chromosome 3. RT-PCR assays showed that StRFP1 was constitutively expressed in potato plants and significantly induced in detached potato leaves by P. infestans and plant defense-related signal molecules, abscisic acid, salicylic acid and methyl jasmonate. Transient expression studies revealed that StRFP1 fused with GFP localized to the plasma membrane or out of that in onion epidermal cells. The function of StRFP1 in potato resistance against late blight was further investigated by constructing overexpression and RNA interference (RNAi) vectors, which were introduced into potato cv. E-potato 3, respectively. By challenging the detached leaves with mixture races of P. infestans, all of the StRFP1-overexpressing plants displayed slower disease development than non-transformed controls in terms of the lesion growth rate (LGR). In contrast, StRFP1-silencing plants through RNAi were more susceptible to pathogen infection. The present results demonstrate that StRFP1 contributes to broad-spectrum resistance against P. infestans in potato.

Comparative cDNA-AFLP analysis reveals that DL-β-amino-butyric acid induces resistance through early activation of the host-defense genes in potato

DL-beta-amino-butyric acid (BABA) has been found to protect potato plants against late blight caused by Phytophthora infestans. This paper compares gene expression profiles of a potato clone harboring horizontal resistance to P. infestans in response to BABA and the pathogen by using cDNA-amplified fragment length polymorphism (cDNA-AFLP), aiming at fudermental elucidation of molecular mechanisms of BABA induced resistance (BABA-IR). In total, 101 transcript derived fragments (TDFs) showed significant differential expression among the treated and their respective control samples. About half of differentially expressed fragments (49) were overlapped in both BABA and P. infestans induction systems, and homology analysis showed that these TDFs in common involved in signaling, cell wall strengthening and synthesis of antimicrobial compounds, reflecting both BABA-IR and the natural resistance shared similar defense mechanisms to a great extent. Analysis of the transcription profiles demonstrated that an early activation of plant basal defense system could be crucial for BABA-IR. Some differentially expressed TDFs homologous to genes encoding proteins related to jasmonic acid-and salicylic acid-dependent signaling pathways, were up-regulated by BABA. Similar genes associated with these pathways were also identified in the pathogen inoculated samples, reinforcing that the extensive cross-talk between BABA-IR and horizontal resistance may be important to coordinate the genes responsible for P. infestans infection in potato.

Conditional QTL underlying resistance to late blight in a diploid potato population

A large number of quantitative trait loci (QTL) for resistance to late blight of potato have been reported with a “conventional” method in which each phenotypic trait reflects the cumulative genetic effects for the duration of the disease process. However, as genes controlling response to disease may have unique contributions with specific temporal features, it is important to consider the phenotype as dynamic. Here, using the net genetic effects evidenced at consecutive time points during disease development, we report the first conditional mapping of QTL underlying late blight resistance in potato under five environments in Peru. Six conditional QTL were mapped, one each on chromosome 2, 7 and 12 and three on chromosome 9. These QTL represent distinct contributions to the phenotypic variation at different stages of disease development. By comparison, when conventional mapping was conducted, only one QTL was detected on chromosome 9. This QTL was the same as one of the conditional QTL. The results imply that conditional QTL reflect genes that function at particular stages during the host–pathogen interaction. The dynamics revealed by conditional QTL mapping could contribute to the understanding of the molecular mechanism of late blight resistance and these QTL could be used to target genes for marker development or manipulation to improve resistance.

A novel leucine-rich repeat receptor-like kinase gene in potato, StLRPK1, is involved in response to diverse stresses

A potato gene, StLRPK1 (Solanum tuberosum L. leucine-rich-repeat receptor-like protein kinases 1), encoding a protein belonging to leucine-rich repeat receptor-like kinases (LRR-RLKs) was identified. It encodes 796 amino acids with 88% of identity to SRF3 of Arabidopsis thaliana and contains a signal peptide, five LRR motifs, a transmembrane domain, two proline-rich regions and a serine/threonine protein kinase domain. The transcripts were present at high levels in flowers and young leaves, while low in other tested organs. The mRNA of StLRPK1 was inducible in potato leaves by Phytophthora infestans, a pathogen causing late blight disease, and showed different profiles after treatment with salicylic acid, methyl jasmonate, ethylene, abscissic acid, wounding, 40°C, 4°C and a salinity stress. The results suggest that StLRPK1 may participate in the responses against environmental stresses and disease resistance in potato.

Potato NPH3/RPT2-Like Protein StNRL1, Targeted by a Phytophthora infestans RXLR Effector, Is a Susceptibility Factor

An effector from the potato late blight pathogen targets a host protein that negatively regulates immunity. Plant pathogens deliver effectors to manipulate host processes. We know little about how fungal and oomycete effectors target host proteins to promote susceptibility, yet such knowledge is vital to understand crop disease. We show that either transient expression in Nicotiana benthamiana, or stable transgenic expression in potato (Solanum tuberosum), of the Phytophthora infestans RXLR effector Pi02860 enhances leaf colonization by the pathogen. Expression of Pi02860 also attenuates cell death triggered by the P. infestans microbe-associated molecular pattern INF1, indicating that the effector suppresses pattern-triggered immunity. However, the effector does not attenuate cell death triggered by Cf4/Avr4 coexpression, showing that it does not suppress all cell death activated by cell surface receptors. Pi02860 interacts in yeast two-hybrid assays with potato NPH3/RPT2-LIKE1 (NRL1), a predicted CULLIN3-associated ubiquitin E3 ligase. Interaction of Pi02860 in planta was confirmed by coimmunoprecipitation and bimolecular fluorescence complementation assays. Virus-induced gene silencing of NRL1 in N. benthamiana resulted in reduced P. infestans colonization and accelerated INF1-mediated cell death, indicating that this host protein acts as a negative regulator of immunity. Moreover, whereas NRL1 virus-induced gene silencing had no effect on the ability of the P. infestans effector Avr3a to suppress INF1-mediated cell death, such suppression by Pi02860 was significantly attenuated, indicating that this activity of Pi02860 is mediated by NRL1. Transient overexpression of NRL1 resulted in the suppression of INF1-mediated cell death and enhanced P. infestans leaf colonization, demonstrating that NRL1 acts as a susceptibility factor to promote late blight disease.

The Potato ERF Transcription Factor StERF3 Negatively Regulates Resistance to Phytophthora infestans and Salt Tolerance in Potato

Ethylene response factors (ERFs) are unique to the plant kingdom and play crucial roles in plant response to various biotic and abiotic stresses. We show here that a potato StERF3, which contains an ERF-associated amphiphilic repression (EAR) motif in its C-terminal region, negatively regulates resistance to Phytophthora infestans and salt tolerance in potato. The StERF3 promoter responds to induction by salicylic acid, ABA ethylene and NaCl, as well as P. infestans, the causal agent of potato late blight disease. StERF3 could bind to the GCC box element of the HIS3 promoter and activate transcription of HIS3 in yeast cells. Importantly, silencing of StERF3 in potato produced an enhanced foliage resistance to P. infestans and elevated plant tolerance to NaCl stress accompanied by the activation of defense-related genes (PR1, NPR1 and WRKY1). In contrast, StERF3-overexpressing plants showed reduced expression of these defense-related genes and enhanced susceptibility to P. infestans, suggesting that StERF3 functions as a negative regulator of downstream defense- and/or stress-related genes in potato. StERF3 is localized to the nucleus. Interestingly, yeast two-hybrid assay and a bimolecular fluorescence complementation (BiFC) test clarified that StERF3 could interact with other proteins in the cytoplasm which may lead to its re-localization between the nucleus and cytoplasm, revealing a novel means of StERF3 regulation. Taken together, these data provide new insights into the mechanism underlying how StERF3 negatively regulates late blight resistance and abiotic tolerance in potato and may have a potential use in engineering late blight resistance in potato.

Functional analysis of potato genes involved in quantitative resistance to Phytophthora infestans

The most significant threat to potato production worldwide is the late blight disease, which is caused by the oomycete pathogen Phytophthora infestans. Based on previous cDNA microarrays and cDNA-amplified fragment length polymorphism analysis, 63 candidate genes that are expected to contribute to developing a durable resistance to late blight were selected for further functional analysis. We performed virus-induced gene silencing (VIGS) to these candidate genes on both Nicotiana benthamiana and potato, subsequently inoculated detached leaves and assessed the resistance level. Ten genes decreased the resistance to P. infestans after VIGS treatment. Among those, a lipoxygenase (LOX; EC 1.13.11.12) and a suberization-associated anionic peroxidase affected the resistance in both N. benthamiana and potato. Our results identify genes that may play a role in quantitative resistance mechanisms to late blight.