Cytokinin oxidase/dehydrogenases (CKXs) play a key role in the irreversible degradation of phytohormone cytokinin that is necessary for various plant growth and development processes. However, thus far, detailed investigations of the CKX gene family in the model legume Medicago truncatula are limited. In this study, we identified 9 putative CKX homologues with conserved FAD- and cytokinin-binding domains in the M. truncatula genome. We analyzed their phylogenetic relationship, gene structure, conserved domain, expression pattern, protein subcellular locations and other properties. The tissue-specific expression profiles of the MtCKX genes are different among different members and these MtCKXs also displayed different patterns in response to synthetic cytokinin 6-benzylaminopurine (6-BA) and indole-3-acetic acid (IAA), suggesting their diverse roles in M. truncatula development. To further understand the biological function of MtCKXs, we identified and characterized mutants of each MtCKX by taking advantage of the Tnt1 mutant population in M. truncatula. Results indicated that M. truncatula plants harboring Tnt1 insertions in each single MtCKX genes showed no morphological changes in aerial parts, suggesting functional redundancy of MtCKXs in M. truncatula shoot development. However, disruption of Medtr4g126160, which is predominantly expressed in roots, leads to an obvious reduced primary root length and increased lateral root number, indicating the specific roles of cytokinin in regulating root architecture. We systematically analyzed the MtCKX gene family at the genome-wide level and revealed their possible roles in M. truncatula shoot and root development, which shed lights on understanding the biological function of CKX family genes in related legume plants.

中文翻译：

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苜蓿细胞分裂素氧化酶/脱氢酶家族基因的全基因组鉴定和表征

细胞分裂素氧化酶/脱氢酶 (CKX) 在植物激素细胞分裂素的不可逆降解中起关键作用，这是各种植物生长和发育过程所必需的。然而，到目前为止，对模型豆科植物苜蓿中 CKX 基因家族的详细研究是有限的。在这项研究中，我们在 M. truncatula 基因组中鉴定了 9 个具有保守的 FAD 和细胞分裂素结合域的推定 CKX 同源物。我们分析了它们的系统发育关系、基因结构、保守域、表达模式、蛋白质亚细胞位置和其他特性。MtCKX 基因的组织特异性表达谱在不同成员之间是不同的，并且这些 MtCKX 也显示出不同的模式响应合成细胞分裂素 6-苄氨基嘌呤（6-BA）和吲哚-3-乙酸（IAA），表明它们在 M. truncatula 发育中的不同作用。为了进一步了解 MtCKXs 的生物学功能，我们通过利用 M. truncatula 中的 Tnt1 突变体群体来鉴定和表征每个 MtCKX 的突变体。结果表明，在每个单独的 MtCKX 基因中含有 Tnt1 插入的 M. truncatula 植物在地上部分没有形态学变化，表明 MtCKXs 在 M. truncatula 枝条发育中的功能冗余。然而，主要在根中表达的 Medtr4g126160 的破坏导致初生根长度明显减少和侧根数增加，表明细胞分裂素在调节根结构中的特定作用。我们在全基因组水平上系统地分析了 MtCKX 基因家族，并揭示了它们在 M. truncatula 芽和根发育中的可能作用，