A MAP guides lateral root initiation

Qian and Wang et al. investigate the function of TPXL5 in lateral root initiation.

By Yanmin Qian

State Key Laboratory of Plant Physiology and Biochemistry; Department of Plant Sciences, College of Biological Sciences, China Agricultural University, Beijing 100193, China

Background: Tight control of lateral root (LR) initiation is vital for root system architecture. During LR initiation, the specific pairs of founder cells expand more in the central domains and less in the peripheral domains. Such an asymmetric radial expansion promotes the subsequent progression and outgrowth of LRs. However, the underlying cellular mechanisms are largely unclear. The reorganization of cortical microtubules is necessary for plant cell expansion, and is regulated by microtubule-associated proteins (MAPs). Microtubules are involved in the early events of LR initiation in Arabidopsis thaliana. However, the MAPs regulating microtubule reorganization during LR initiation remain unclear.

Question: We want to know whether and how specific MAPs mediate LR initiation by regulating microtubule reorganization.

Findings: We found that a microtubule-stabilizing protein TPX2-LIKE5 (TPXL5) participates in LR initiation. In the tpxl5 mutant, the radial expansion in the peripheral domain of LR founder cells after the first asymmetric division was stronger than that in wildtype, and the ordered transverse cortical microtubule arrays were not well generated. Moreover, transcription factor ELONGATED HYPOCOTYL5 (HY5) downregulated TPXL5 expression. Mutant hy5 exhibited the opposite phenotype compared to the tpxl5 mutant. Our study demonstrates that TPXL5 positively regulates cortical microtubules reorganization in the peripheral domain, thus promoting the asymmetric radial expansion of founder cells during LR initiation. It also reveals a novel molecular mechanism by which HY5 regulates TPXL5-mediated cortical microtubule reorganization and cell remodeling during LR initiation.

Next steps: In future study, we will focus on how microtubule organization are specifically regulated in the peripheral and central domains of the founder cells. We will also study whether there is a feedback mechanism between cortical microtubules and auxin signals in HY5-mediated LR development.

Yanmin Qian, Xiaohong Wang, Yimin Liu, Xiangfeng Wang, and Tonglin Mao. (2023). HY5 inhibits lateral root initiation in Arabidopsis through negative regulation of the microtubule-stabilizing protein TPXL5. https://doi.org/10.1093/plcell/koac358