Genome-Wide Identification and Expression Profiling Analysis of the Aux/IAA Gene Family in Medicago truncatula during the Early Phase of Sinorhizobium meliloti Infection

BackgroundAuxin/indoleacetic acid (Aux/IAA) genes, coding a family of short-lived nuclear proteins, play key roles in wide variety of plant developmental processes, including root system regulation and responses to environmental stimulus. However, how they function in auxin signaling pathway and symbiosis with rhizobial in Medicago truncatula are largely unknown. The present study aims at gaining deeper insight on distinctive expression and function features of Aux/IAA family genes in Medicago truncatula during nodule formation.Principal FindingsUsing the latest updated draft of the full Medicago truncatula genome, a comprehensive identification and analysis of IAA genes were performed. The data indicated that MtIAA family genes are distributed in all the M. truncatula chromosomes except chromosome 6. Most of MtIAA genes are responsive to exogenous auxin and express in tissues-specific manner. To understand the biological functions of MtIAA genes involved in nodule formation, quantitative real-time polymerase chain reaction (qRT-PCR) was used to test the expression profiling of MtIAA genes during the early phase of Sinorhizobium meliloti (S. meliloti) infection. The expression patterns of most MtIAA genes were down-regulated in roots and up-regulated in shoots by S. meliloti infection. The differences in expression responses between roots and shoots caused by S. meliloti infection were alleviated by 1-NOA application.ConclusionThe genome-wide identification, evolution and expression pattern analysis of MtIAA genes were performed in this study. The data helps us to understand the roles of MtIAA-mediated auxin signaling in nodule formation during the early phase of S. meliloti infection.

背景：生长素/吲哚乙酸（Auxin/indoleacetic acid, Aux/IAA）基因编码一类短命核蛋白，在诸多植物发育进程中发挥关键调控作用，涵盖根系系统构建与环境刺激响应等过程。然而，蒺藜苜蓿（Medicago truncatula）中该家族基因如何参与生长素信号通路，以及与根瘤菌共生的分子机制仍未完全明晰。本研究旨在深入解析蒺藜苜蓿Aux/IAA家族基因在根瘤形成过程中的独特表达与功能特征。主要研究结果：借助最新更新的蒺藜苜蓿全基因组草图，研究人员对IAA基因家族开展了全面的鉴定与系统性分析。结果显示，MtIAA家族基因分布于除第6号染色体外的所有蒺藜苜蓿染色体上。绝大多数MtIAA基因对外源生长素具有响应性，且呈现组织特异性表达模式。为探究参与根瘤形成的MtIAA基因的生物学功能，本研究采用实时荧光定量聚合酶链式反应（quantitative real-time polymerase chain reaction, qRT-PCR）技术，检测了苜蓿中华根瘤菌（Sinorhizobium meliloti, S. meliloti）侵染早期阶段MtIAA基因的表达谱。数据分析表明，多数MtIAA基因在根部受中华根瘤菌侵染后表达下调，而在地上组织中则表达上调。1-NOA处理可缓解中华根瘤菌侵染所引发的根与地上组织间的表达差异。结论：本研究完成了蒺藜苜蓿MtIAA基因的全基因组鉴定、进化分析以及表达模式解析。相关研究数据有助于阐明中华根瘤菌侵染早期，MtIAA介导的生长素信号通路在根瘤形成过程中的调控作用。