Investigating the interplay of auxin signaling and PLETHORA 7 during de novo root regeneration

Abstract

The regenerative abilities of plants range from the individual cells, tissues, and organs to the complete rebuilding of the whole organism. Over the years, Arabidopsis thaliana, a model organism, has provided insights into the mechanisms underlying plant regeneration. Regenerative response in A. thaliana can be categorized into two basic categories, tissue culture-induced regeneration and mechanical injury-induced regeneration. De novo root regeneration (DNRR) is a plant regeneration caused by mechanical injury in which it demonstrated that the mechanical injury-induced regeneration in A. thaliana excised leaf generates adventitious roots when in contact with a substrate or wound healing response in the form of a callus when the cut end is kept untouched. Previous research showed that the DNRR response in A. thaliana is controlled by transcriptional factors such as PLETHORAs (PLTs). During de novo root organogenesis, endogenic auxin plays a critical role to achieve a fate transition of regeneration- competent cells to become the root founder cells. However, it is not well understood how the PLETHORA 7 and auxin response pathways interact and affect each other during de novo root regeneration. Therefore, the main aim of this project is to uncover the interplay of the auxin and PLT7 in A. thaliana during regenerative response. The results indicate a significant increase in the expression level of PLT7 upon inhibition of auxin signaling. However, the de novo root regenerative assay conducted on the transgenic line (pG1090:XVE::axr3-1-RFP) revealed a complete abolishment of de novo root regeneration following a 15-minute of estradiol induction. Utilizing double marker lines, we examined the expression pattern of PLT7 in the axr3-1 with 15 minutes of estradiol induction and observed that despite the increase in PLT7 expression level, it was not localized near the injury sites but rather distally from the petiole section. The expression pattern of PLT7 in the context of auxin signaling inhibition differed from the normal PLT7 expression pattern observed in regenerative perspectives during de novo root regeneration (DNRR). Thus, indicating proper spatiotemporal activity of PLT7 is critical to initiate DNRR not necessarily just the global expression itself.