Recently, Prof. Ding Zhaojun from School of Life Sciences, Key Laboratory of Plant Development and Environmental Adaptation Biology, Ministry of education, Shandong University, published his research paper entitled "Antagonistic interaction between auxin and SA signaling pathways regulations bacterial infection through lateral root in Arabidopsis" in Cell Reports. Assistant researcher Kong Xiangpei and postdoctoral Zhang Chunlei are the co-first authors and Prof. Ding Zhaojun and assistant researcher Kong Xiangpei are the co-corresponding authors of this paper.

Plant pathogens deploy a variety of sophisticated strategies to invade their hosts where they thenaccess nutrients and water from hosts for their growth.Plant surfaces, such as stomata, provide entry sites for pathogens. It has been reported that stomata play an important role in limiting bacterial invasion as part of the plant innate immune system.

Besides anchoring plants into the soil, plant roots are important for the uptake of water and nutrients and, therefore, play a fundamental role in plant growth and development. The plant root rhizosphere is densely populated by microorganisms, including fungi, bacteria, and nematodes.It has been reported that the Arabidopsis immune receptor kinase FLAGELLIN-SENSING 2 (FLS2) is mainly expressed in thestelestarting at the root differentiation zone andoutgrowinglateral roots (LRs), and flagellin 22 (flg22)can also triggerpattern-triggered immunity (PTI)responsesin root, indicating that theroot acts as an important part of plant innate immune system.

The LRP emerges through the overlaying endodermal, cortical and epidermal cell layers to form a lateral root.Here, using GFP-labeled pathogenic bacterium Pseudomonas syringaepv.tomato strain DC3000 (PtoDC3000), the authors observed that the virulent PtoDC3000 invaded plants through emerged LRs in Arabidopsis. Interestingly, the authors observed that pathogens, such as PtoDC3000, strongly induced LR formation, a process that was dependent on ARF7/ARF19-LBDs mediated-auxin signaling.In addition,the phytotoxinscoronatine (COR)and type-III-secretion-system effectors (T3SEs) are also involved in P. syringae-triggered LR development. On the other hand, the plant defense hormone SA inhibits LR formation through ARF7. Overexpression of PR1 and PR2 partially blocked the PtoDC3000-induced LRE. The authors also showed that ARF7 proteins directly bind to the promoters ofPR1 and PR2 and repress the transcription of these two genes.

Taken together, these results highlight the antagonistic interaction between auxin and SA signaling pathways in lateral root development and their roles in controlling bacterial infection through lateral root.

This work is supported by the National Natural Science Foundation of China, by the Shandong Province Natural Science Foundation of Major Basic Research Program, and by the Young Scholars Program of Shandong University, and the Key Research and Development Projects of Shandong Province, and by the Youth Interdisciplinary Science and Innovative Research Groups of Shandong University.

Written by：Kong Xiangpei

Edited by：Che Huiqing