title: The lss supernodulation mutant of Medicago truncatula reduces expression of the SUNN gene.
abstract: The number of nodules that form in a legume when interacting with compatible rhizobia is regulated by the plant. We report the identification of a mutant in nodule regulation in Medicago truncatula, like sunn supernodulator (lss), which displays shoot-controlled supernodulation and short roots, similar to sunn mutants. In contrast with the sunn-1 mutant, nodulation in the lss mutant is more extensive and is less sensitive to nitrate and ethylene, resembling the sunn-4 presumed null allele phenotype. Although the lss locus maps to the SUNN region of linkage group 4 and sunn and lss do not complement each other, there is no mutation in the genomic copy of the SUNN gene or in the 15-kb surrounding region in the lss mutant. However, expression of the SUNN gene in the shoots of lss plants is greatly reduced compared with wild-type plants. Analysis of cDNA from plants heterozygous for lss indicates that lss is a cis-acting factor affecting the expression of SUNN, and documented reversion events show it to be unstable, suggesting a possible reversible DNA rearrangement or an epigenetic change in the lss mutant. Assessment of the SUNN promoter revealed low levels of cytosine methylation in the 700-bp region proximal to the predicted transcription start site in both wild-type and lss plants, indicating that promoter hypermethylation is not responsible for the suppression of SUNN expression in lss. Thus, lss represents either a distal novel locus within the mapped region affecting SUNN expression or an uncharacterized epigenetic modification at the SUNN locus.
authors.affiliation: Department of Genetics and Biochemistry, Clemson University, Clemson, South Carolina 29634, USA.
authors.forename: Elise
authors.initials: E
authors.lastname: Schnabel
authors.forename: Arijit
authors.initials: A
authors.lastname: Mukherjee
authors.forename: Lucinda
authors.initials: L
authors.lastname: Smith
authors.forename: Tessema
authors.initials: T
authors.lastname: Kassaw
authors.forename: Sharon
authors.initials: S
authors.lastname: Long
authors.forename: Julia
authors.initials: J
authors.lastname: Frugoli
mesh_terms: D002874:Chromosome Mapping; D019175:DNA Methylation; D018744:DNA, Plant / Q000235:genetics; D057890:Epigenomics; D005030:Ethylenes / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D046913:Medicago truncatula / Q000235:genetics* / Q000378:metabolism; D009154:Mutation; D010641:Phenotype; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D055170:Plant Root Nodulation
chemical_list: D018744:DNA, Plant; D005030:Ethylenes; D010940:Plant Proteins; C036216:ethylene