blkn, a novel Medicago truncatula mutant achieving black nodule phenotype

Abstract

blkn is a Medicago truncatula mutant that is achieving null function-black nodule phenotype. blkn is a Tnt1-retrotransposon mutant, Tnt1 is Nicotiana tabacum retro-transposon which is replicated via RNA copy and integrated in plant genome. Interestingly, blkn exhibited double contents of phenolic compounds comparing to R108 wild type. The mutated black nodule is displaying cells abnormality in both infection and nitrogen fixation zones. Transverse section of blkn nodule doesn’t display clearly characteristic shape like the control and the symbiotic cells don't totally filled with bacteroids along with high lignification at the cell wall periphery. Our goal was blkn mutant; phenotype, physiological, and molecular characterizations. AFLP-based PCR method was used to detect the mutated gene(s) in this mutant line. About 25 Tnt1-tagged fragments ranging from ~100 to ~500 bp were isolated, sequenced and submitted to Genbank. The Tnt1 insertion was precisely located next to the base number 303 post ATG start codon of M. truncatula L-type lectin-domain receptor kinase VII.2 gene encodes Lectin_LegB Receptor Like Kinase (MtLectinRLK). MtLectinRLK contains Lectin_legB domain, two transmembrane helix (TMhilex) and an extracellular Receptor Protein kinase (Pkinase). MtLectinRLK is an ancestry related to probable L-type lectin-domain containing receptor kinase Cicer arietinum, Trifolium pretense, Phaseolus vulgaris, Vigna radiate and Glycine soja.