The plant hormone indole-3-acetic acid (IAA), also known as auxin, plays important roles in plant growth and development, as well as in several plant–microbe interactions. IAA also acts as a microbial signal and in many bacteria regulates metabolism, stress responses, and virulence. In the bacterial plant pathogen Pseudomonas syringae pv. tomato strain DC3000 (PtoDC3000), exposure to IAA results in large-scale transcriptional reprogramming, including the differential expression of several known virulence genes. However, how PtoDC3000 senses and responds to IAA and what aspects of its biology are regulated by IAA is not understood. To investigate the mechanisms involved in perceiving and responding to IAA, we carried out a genetic screen for mutants with altered responses to IAA. One group of mutants of particular interest carried disruptions in the aefR gene encoding a TetR family transcriptional regulator. Gene expression analysis confirmed that the aefR mutants have altered responses to IAA. Thus, AefR is the first demonstrated auxin response regulator in PtoDC3000. We also investigated several aspects of PtoDC3000 biology that are regulated by both AefR and IAA, including antibiotic resistance, motility, and virulence. The observation that the aefR mutant has altered virulence on Arabidopsis, suggests that the sector of the IAA response regulated by aefR is important during pathogenesis. Our findings also provide evidence that AefR plays a role in coordinating changes in gene expression during the transition from early to late stages of infection.

Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

植物激素吲哚-3-乙酸 (IAA)，也称为生长素，在植物生长和发育以及多种植物与微生物相互作用中发挥着重要作用。 IAA 还充当微生物信号，在许多细菌中调节新陈代谢、应激反应和毒力。在细菌植物病原体丁香假单胞菌pv。番茄菌株 DC3000 ( Pto DC3000) 暴露于 IAA 会导致大规模转录重编程，包括几个已知毒力基因的差异表达。然而，Pto DC3000 如何感知和响应 IAA 以及其生物学的哪些方面受 IAA 调节尚不清楚。为了研究感知和响应 IAA 的机制，我们对 IAA 反应发生改变的突变体进行了基因筛选。一组特别令人感兴趣的突变体编码 TetR 家族转录调节因子的aefR基因遭到破坏。基因表达分析证实aefR突变体改变了对 IAA 的反应。因此，AefR 是Pto DC3000中第一个被证明的生长素反应调节剂。我们还研究了Pto DC3000 生物学受 AefR 和 IAA 调节的几个方面，包括抗生素耐药性、运动性和毒力。aefR突变体改变了拟南芥的毒力，这表明aefR调节的 IAA 反应部分在发病机制中很重要。我们的研究结果还提供了证据，表明 AefR 在感染早期到晚期的过渡过程中在协调基因表达变化方面发挥着作用。

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