Abstract: Plant height is one of the most important agronomic traits that determines the lodging resistance and biomass yield in crops. However, the molecular mechanism underlying the stem elongation in forage legumes is poorly understood. In this study, we isolated and characterized a dwarf mutant compact stalk internodes (costin) by screening Tnt1 retrotransposon-tagged lines of M. truncatula. Results showed that the dwarf phenotype of costin is caused by inhibition of the internode elongation. We cloned COSTIN by PCR-based genotyping of flanking sequence tags (FST) in segregating populations. The COSTIN gene encodes a calcium exchanger protein, which is homologue to Arabidopsis CALCIUM EXCHANGER 7(CAX7). qRT-PCR analysis revealed that COSTIN is highly expressed in stem, leaf and pod. 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.

Key words: M. truncatula, plant height, COSTIN, calcium exchanger protein, gibberellic acid

摘要： 株高是影响植物株型建成的重要农艺性状之一，直接决定作物的倒伏性和生物产量，但目前关于苜蓿等豆科牧草株高性状形成的分子调控机制尚不清楚。通过定向筛选豆科模式植物蒺藜苜蓿Tnt1逆转座子插入突变体库，分离鉴定了一个蒺藜苜蓿矮化突变体compact stalk internodes(costin)，该突变体的矮化表型是由于茎节伸长受到抑制所致。通过基因表型连锁分析成功克隆了COSTIN基因，该基因编码一个钙离子交换蛋白，与拟南芥的CALCIUM EXCHANGER 7(CAX7) 基因高度同源。qRT-PCR检测发现COSTIN基因在茎、叶和果荚等组织中有较高的表达。进一步研究发现在costin突变体中赤霉素合成途径关键基因MtCPS、MtKAO1、MtGA20ox4、MtGA20ox7和MtGA3ox1表达下调；外施赤霉素GA3可以恢复costin突变体的矮化表型。上述研究表明COSTIN基因通过影响植物激素赤霉素的生物合成来调控蒺藜苜蓿的茎节伸长。

关键词: 蒺藜苜蓿, 株高, COSTIN, 钙离子交换蛋白, 赤霉素