Identification And Characterization Of The Compact STALK INTERNODES (COSTIN) Gene Required For Plant Height In Model Legume Medicago Truncatula

Plant height is one of the most important agricultural traits that determines the lodging resistance and biomass yield in crops.However,the underlying molecular mechanism of the stem elongation controling in forage legumes is poorly understood.In this study,a dwarf mutant compact stalk internodes?costin?was isolated and characterized by the Tnt1retrotransposon-tagged lines of M.truncatula screening.The costin mutant and the preliminary researches on its phenotype provided both genetic stock and research strategy for genetic improvement of excellent characters on M.truncatula.The main results are as follows:1.A dwarf mutant NF15084 was isolated and characterized by Tnt1retrotransposon-tagged lines of M.truncatula screening,and then named compact stalk internodes?costin?,whose dwarf phenotype was caused by inhibition of the internode elongation during the second and the third compound leaf numbered from the bottom.2.The COSTIN gene was cloned by PCR-based genotyping of flanking sequence tags?FST?in segregating populations.It encodes a calcium exchanger protein,whose amino acid sequence shares 50%homology with the CALCIUM EXCHANGER 7?CAX7?in Arabidopsis.qRT-PCR analysis revealed that COSTIN gene was highly expressed in stem,simple leaf and pod.3.The dwarf phenotype of costin was caused by inhibition of the internode elongation.Moreover,several gibberellic acid?GA?biosynthesis pathway genes including MtCPS,MtKAO1,MtGA20ox4,MtGA20ox7 and MtGA3ox1 were significantly downregulated in the costin mutant,and the dwarf phenotype of costin could be rescued by exogenous application with gibberellic acid-3?GA₃?.These data together demonstrated that the COSTIN gene control internode elongation through regulating the biosynthesis of the phytohormone gibberellic acid in M.truncatula.