Dissecting Genetic and Molecular Mechanisms of Nodulation in Cultivated Peanut (Arachis hypogaea. L).

Symbiosis in leguminous plant is an important trait that contributes to their yield and vigor through atmospheric nitrogen fixation. The symbiotic process is made possible in root nodules by the mutualistic association between leguminous plants and bacteria known as rhizobia. The molecular mechanisms of this association in cultivated peanut with a ‘crack entry’ infection process is not well studied and little is known about the genetics of peanut nodulation. The goal of this research is to genetically map nodulation genes in cultivated peanut, to subsequently clone and characterize the genes. A F₂ mapping population was developed from a cross between a pair of non-nodulating (Nod-) and nodulating (Nod+) sister inbred lines, E4 (Nod-) and E5 (Nod+), which were derived from a cross between two nodulating (+) peanut lines (PI292060 - Robore, Bolivia and UF 487A- a breeding line from University of Florida). A total of 542 F₂ individuals were obtained in 2014. Nodulation phenotype were recorded during harvesting, resulting a 9 (Nod+): 7 (Nod-) segregating ratio, indicating that two genes were segregating in this population. Simple sequence repeat (SSR) markers were used to genotype a sub-population, which mapped a quantitative trait locus (QTL) on chromosome B07. A Further genotyping of the whole population with seven SSR markers on chromosome B07 mapped the QTL to a 2.89 cM interval flanked by two SSR markers, AHGS1100 and AHGS3316. Five out of seven differentially expressed genes (DEGs) between E4 and E5 on chromosome B07 from our RNAseq were found in the QTL region. Gene expression of these five DEG will be further characterized using qRT-PCR. The results of this study will unmask the genes, functions and the mystery behind the nodulation of cultivated peanut, which could be further used to improve the nitrogen fixation capacity of other leguminous and non-legumious plant.

KEY WORDS: Nodulation; Peanut; Sister Inbred lines; Mapping population; Genotype; Phenotype; Linkage map; QTL; Differentially Expressed Genes.