The phylogenetic relationship of possible progenitors of the cultivated peanut

The cultivated peanut (Arachis hypogaea L.) is an allotetraploid composed of A and B genomes. The phylogenetic relationship among the cultivated peanut, wild diploid, and tetraploid species in the section Arachis was studied based on sequence comparison of stearoyl-ACP desaturase and oleoyl-PC desaturase. The topology of the trees for both fatty acid desaturases displayed two clusters; one cluster with A genome diploid species and the other with B genome diploid species. The two homeologous genes obtained for each of the two fatty acid desaturases from the tetraploid species A. hypogaea and A. monticola were separated into the A and B genome clusters, respectively. The gene phylogenetic trees showed that A. hypogaea is more closely related to the diploid species A. duranensis and A. ipaensis than to the wild tetraploid species A. monticola, suggesting that A. monticola is not a progenitor of the cultivated peanut. In addition, for the stearoyl-ACP desaturase, the A. duranensis sequence was identical with one of the sequences of A. hypogaea and the A. ipaensis sequence was identical with the other. These results support the hypothesis that A. duranensis and A. ipaensis are the most likely diploid progenitors of the cultivated tetraploid A. hypogaea.     

An integrated genetic linkage map of cultivated peanut (Arachis hypogaea L.) constructed from two RIL populations

Construction and improvement of a genetic map for peanut (Arachis hypogaea L.) continues to be an important task in order to facilitate quantitative trait locus (QTL) analysis and the development of tools for marker-assisted breeding. The objective of this study was to develop a comparative integrated map from two cultivated × cultivated recombinant inbred line (RIL) mapping populations and to apply in mapping Tomato spotted wilt virus (TSWV) resistance trait in peanut. A total of 4,576 simple sequence repeat (SSR) markers from three sources: published SSR markers, newly developed SSR markers from expressed sequence tags (EST) and from bacterial artificial chromosome end-sequences were used for screening polymorphisms. Two cleaved amplified polymorphic sequence markers were also included to differentiate ahFAD2A alleles and ahFAD2B alleles. A total of 324 markers were anchored on this integrated map covering 1,352.1 cM with 21 linkage groups (LGs). Combining information from duplicated loci between LGs and comparing with published diploid maps, seven homoeologous groups were defined and 17 LGs (A1-A10, B1-B4, B7, B8, and B9) were aligned to corresponding A-subgenome or B-subgenome of diploid progenitors. One reciprocal translocation was confirmed in the tetraploid-cultivated peanut genome. Several chromosomal rearrangements were observed by comparing with published cultivated peanut maps. High consistency with cultivated peanut maps derived from different populations may support this integrated map as a reliable reference map for peanut whole genome sequencing assembling. Further two major QTLs for TSWV resistance were identified for each RILs, which illustrated the application of this map.     

Endoplasmic oleoyl-PC desaturase references the second double bond

The regiospecificity for the gene product of fad2,(1) the microsomal oleoyl-PC desaturase from higher plants, differs from some previous suggestions. Rather than only referencing the carboxyl group (a Delta(12) desaturase) or the methyl terminus (an omega-6 desaturase), this desaturase locates the second double bond in its substrates by first referencing the existing double bond. This specificity was demonstrated for the oleoyl-PC desaturase cDNA from the developing seeds of peanut (Arachis hypogaea L) expressed in yeast (Saccharomyces cerevisae). The expressed enzyme was capable of desaturating monounsaturated fatty acyl groups in membrane lipids. Endogenous palmitoleate was desaturated to cis, cis 9,12 hexadecadienoate (9(Z)12(Z)C16:2), endogenous oleate to linoleate (9(Z)12(Z) octadecadienoate), and cis 10-nonadecenoate (provided as a supplement in the growth medium) to 10(Z)13(Z)C19:2. The rule, Delta(x+3) where x=9 is the double bond location in the substrate, best describes the consistent placement of the second double bond in the above monounsaturated substrates for the oleoyl-PC desaturase of higher plants.     

高油酸花生（Arachis hypogaea L.）杂交后代ahFAD2B的基因鉴评

本研究利用等位基因特异性PCR技术(AS-PCR,allele-specific PCR)对高油酸父本CTWE与4个低油酸母本组配的330个杂交后代进行分子鉴评,其中230个获得了539 bp的特异性条带。白沙1016×CTWE、海花1号×CTWE、冀0212-2×CTWE以及远杂9847×CTWE的真杂种百分率分别为83.3%、50.0%、57.1%和50.0%。本研究采用单粒近红外光谱分析法对F2:3家系进行检测,结果表明远杂9847×CTWE、白沙1016×CTWE、冀0212-2×CTWE以及海花1号×CTWE的F2:3家系中,全部为高油酸类型的家系分别为9个、8个、2个和3个,推断F2群体中,基因型为FAD2B-m/FAD2B-m的个体的比例为9.47%、4.17%、3.39%和3.37%。4个杂交组合高油酸性状的遗传在P=0.05水平上符合2对基因的遗传模式。本研究结果对于高油酸性状的分子鉴定、高油酸花生新品种的培育以及育种效率的提高具有一定的参考价值。     

Inheritance of disease lesion mimic leaf trait in groundnut

In groundnut, two identical mutants with disease lesion mimic leaf trait were isolated independently from two different parents through induced mutagenesis and in vitro culture technique. The leaf chlorophyll content in both the mutants was found to be drastically reduced. The segregation pattern in the F(2) and F(3) generations for normal and mutant traits fitted a 13:3 ratio, indicating that the disease lesion mimic trait in the mutants was due to suppressive gene action. Both mutants were allelic for the disease mimic trait.