Microcystis aeruginosa exudate alters root development by impacting plant hormone accumulation and auxin signal transduction

Microcystis aeruginosa, a typical cyanobacterial species, can alter the root development of aquatic plants. To explore how M. aeruginosa affects plant root development, we exposed Arabidopsis thaliana to M. aeruginosa exudate (MaE) and investigated the responses of plant hormone synthesis and auxin signal transduction. Results showed that MaE significantly advanced lateral root primordium development, increased lateral root number, and reduced primary root length. On the 7th day of MaE exposure, the level of cytokinin in the total roots of A. thaliana decreased, consistent with the decreased expression of cytokinin synthesis and metabolism genes on Day 5 and Day 7. The pathogen defense hormones salicylic acid (SA) and N-(jasmonate)-S-JA-Ile(JA-Ile) concentration significantly increased in MaE-treated roots, although their synthesis and metabolism genes expression level were down-regulated. Similarly, although auxin compounds concentration in roots showed no significant difference, their synthesis and metabolism genes expression level were down-regulated. In the auxin signal transduction pathway, auxin signal input remained unchanged between MaE and the control group, as indicated by DII expression levels, while auxin signal output was amplified by MaE, as shown by increased DR5 expression levels. The transcription factor ARF7, which controls lateral root development and is downstream in the auxin signal transduction pathway, was significantly activated by MaE. These results indicate that MaE affects plant root system architecture by altering plant hormone balance and auxin signal transduction.