HBI1 integrates hormonal and environmental signals to regulate the trade-off between growth and immunity (ChIP-seq). Arabidopsis thaliana

The trade-off between growth and immunity is crucial for survival in plants. An antagonistic interaction has been observed between the growth-promoting hormone brassinosteroid and pathogen associated molecular pattern (PAMP) signals, which induce immunity but inhibit growth, however the underlying molecular mechanism has remained unclear. The PRE-IBH1-HBI1 triple helix-loop-helix/basic helix-loop-helix (HLH/bHLH) cascade has been shown to mediate growth responses to several hormonal and environmental signals, but its downstream targets and role in immunity remain unknown. Here, we performed genome-wide analyses of HBI1 target genes in Arabidopsis. The results show that HBI1 regulates a set of genes that largely overlaps with targets of PIFs, but displays both similar and unique transcriptional activities compared to PIFs, supporting a role in fine-tuning the network through cooperation and antagonism with other DNA-binding factors of the network. Furthermore, HBI1 also negatively regulates a subset of defense response genes. Two PAMPs, flagellin and elongation factor, repressed HBI1 expression, whereas overexpression of HBI1 reduced the PAMP-induced growth inhibition, defense gene expression, reactive oxygen species (ROS) production, and flg22-induced resistance to Pseudomonas syringae pathovar tomato DC3000. These data indicate that HBI1 is a node for crosstalk between hormone and immune pathways. This study demonstrates that the PRE-IBH1-HBI1 module integrates hormone and pathogen signals, and thus plays a central role in the balance between growth and immunity in plants. Overall design: Genome wide analysis the HBI1 binding target

植物生长与免疫之间的权衡对其存活至关重要。目前已观察到促进生长的激素油菜素内酯（brassinosteroid）与可诱导免疫却抑制生长的病原体相关分子模式（pathogen associated molecular pattern, PAMP）信号之间存在拮抗相互作用，但其背后的分子机制仍不明确。PRE-IBH1-HBI1三螺旋-环-螺旋/碱性螺旋-环-螺旋（helix-loop-helix/basic helix-loop-helix, HLH/bHLH）级联反应已被证实可介导植物对多种激素及环境信号的生长响应，但其下游靶基因以及在免疫中的作用仍属未知。本研究对拟南芥（Arabidopsis）中HBI1的靶基因开展了全基因组分析。结果显示，HBI1调控的基因集合与PIFs的靶基因存在大量重叠，但与PIFs相比，其转录活性兼具相似性与独特性，这支持其通过与该调控网络中的其他DNA结合因子协同或拮抗，实现对网络的精细调控的功能。此外，HBI1还可负调控一类防御响应基因。两种PAMP，即鞭毛蛋白（flagellin）与延伸因子（elongation factor），可抑制HBI1的表达；而HBI1过表达则可减轻PAMP诱导的生长抑制、防御基因表达上调、活性氧（reactive oxygen species, ROS）爆发，以及flg22诱导的对丁香假单胞菌番茄致病变种DC3000的抗性。上述数据表明，HBI1是激素与免疫通路之间交叉对话的关键节点。本研究证实，PRE-IBH1-HBI1模块可整合激素与病原体信号，从而在植物生长与免疫的平衡中发挥核心作用。实验整体设计：拟南芥HBI1结合靶基因的全基因组分析