Molecular cloning and characterization of NPR1 gene from Arachis hypogaea.

The NPR1 gene was an important regulator for a plant disease resistance. The cDNA of NPR1 gene was cloned from peanut cultivar Ri Hua 1 by rapid amplification of cDNA ends-polymerase chain reaction (RACE-PCR). The full length cDNA of Arachis hypogaea NPR1 consisted of 2,078 base pairs with a 1,446 bp open-reading frame encoding 481 amino acids. The predicted NPR1 contained the highly conserved functional domains (BTB/POZ domain from M1 to D116), protein-protein interaction domains (three ankyrin repeats from K158 to L186; N187 to L217 and R221 to D250) and one NPR1-like domain (C262 to S469). The DNA sequence of the NPR1 gene was 2,332 or 2,223 bp. Both two sequences contained three introns and four exons. The NPR1 transcripts were expressed mainly in roots and leaves, while fewer signals were detected in the stems. Amount of the NPR1 transcript was significantly increased 1 h after salicylic acid challenge and was eventually 5.3 times greater than that in the control group. Both the DNA sequence and the coding sequence were obtained from eight cultivars and nine wild species of Arachis. Maximum likelihood analyses of d N/d S ratios for 25 sequences from different species showed that different selection pressures may have acted on different branches.

Isolation and analysis of differentially expressed genes from peanut in response to challenge with Ralstonia solanacearum

Background: Bacterial wilt caused by Ralstonia solanacearum is the most devastating disease in peanut. Planting resistant peanut cultivars is deemed as the sole economically viable means for effective control of the disease. To understand the molecular mechanism underlying resistance and facilitate breeding process, differences in gene expression between seeds of Rihua 1 (a Virginia type peanut variety resistant to bacterial wilt) inoculated with the bacterial pathogen suspension (10(9) cfu ml-1) and seeds of the same cultivar treated with water (control), were studied using the GenefishingTM technology. Results: A total of 25 differentially expressed genes were isolated. Expression of genes encoding cyclophilin and ADP-ribosylation factor, respectively, were further studied by real time RT-PCR, and full length cDNAs of both genes were obtained by rapid amplification of cDNA ends. Conclusions: The study provided candidate genes potentially useful for breeding peanut cultivars with both high yield and bacterial wilt resistance, although confirmation of their functions through transgenic studies is still needed.

Identification of a novel mutation in FAD2B from a peanut EMS mutant with elevated oleate content.

A Virginia type peanut mutant with more than 60% oleate content (E2-4-83-12) was selected from an EMS mutagenized population of LF2 (an export type peanut cultivar with 44.2% oleate) by near infrared reflectance spectroscopy. Cloning and sequencing of FAD2B from LF2 and E2-4-83-12 identified a novel mutation (C313T in the coding region) causing an H105Y substitution in the first histidine box of the FAD2B protein. GC-MS analysis of fatty acids in yeast cells harboring pYES2 with the mutated FAD2B detected no linoleate, confirming that FAD2B from E2-4-83-12 was dysfunctional. Loss-of-function FAD2A and FAD2B together contributed to elevated oleate phenotype of the peanut EMS mutant.

Identification of chilling-responsive transcripts in peanut (Arachis hypogaea L. )

To isolate differentially expressed peanut genes responsive to chilling, a suppression subtractive hybridization (SSH) cDNA library was constructed for a chilling tolerant peanut cultivar A4 with mRNAs extracted from the seeds imbibed at 2ºC and 15ºC, respectively, for 24 hrs. A total of 466 cDNA clones were sequenced, from which 193 unique transcripts (73 contigs and 120 singlets) were assembled. Of these unique transcripts, 132 (68.4 percent) were significantly similar to the sequences in GenBank non-redundant (nr) protein database, which belonged to diverse functional categories including metabolism, signal transduction, stress response, cell defense and transcriptional regulation. The remaining 61 (31.6 percent) showed no similarity to either hypothetical or known proteins. Six differentially expressed transcripts were further confirmed with real-time quantitative PCR (RT-qPCR).

Sodium azide mutagenesis resulted in a peanut plant with elevated oleate content

Screening of peanut seeds resulting from 0.39 percent sodium azide treatment with NIRS calibration equation for bulk seed samples identified a plant with more than 60 percent oleate. Oleate content in individual seeds of the plant, as predicted by NIRS calibration equation for intact single peanut seeds, ranged from 50.05 percent ~ 68.69 percent. Three seeds with >60 percent oleate thus identified were further confirmed by gas chromatography. Multiple sequence alignments of the FAD2B gene from Huayu 22 (wild type) and peanut seeds with elevated oleate (mutant type) revealed a C281T transition in the coding region causing an I94T substitution in the oleoyl-PC desaturase, which may be responsible for reduction in the enzyme activity.

Novel protocol to identify true hybrids in normal oleate x high oleate crosses in peanut

A novel hybrid identification protocol was developed for F0:1 peanut seeds resulting from crosses between normal oleate cultivars with wild type FAD2B gene and high oleate genotypes with an A insertion in FAD2B gene. Presence of a series of overlapped peaks in trace file of the PCR product amplified with bF19/R1 primers was an indication of hybridity. This protocol may facilitate high oleate breeding and genetic studies in peanut.

Simple method to prepare DNA templates from a slice of peanut cotyledonary tissue for polymerase chain reaction

An efficient DNA extraction method was developed for peanut seed, where only 3-5 mg cotyledonary tissue was enough for more than 50 PCR reactions with a reaction volume of 15 ul. Both low copy number and high copy number DNA sequences were successfully amplified. Processing one seed sample only took about half an hour. Sampling had no significant effects on germination and development. The DNA extraction method makes it possible to identify transformants and conduct molecular marker studies prior to sowing, and thus may greatly hasten research progress.

A rapid and cheap protocol for preparation of PCR templates in peanut

This paper describes a simple, low cost and reliable DNA template preparation protocol for polymerase chain reaction (PCR) using immature leaves from peanut seeds or leaves from field-grown plants. The technique may find wide utility in studies involving PCR-based molecular markers, rapid screening for transformants and gene cloning.