Cadmium stress suppresses lateral root formation by interfering with the root clock

Abstract

A biological clock activated by oscillating signals, known as root clock, has been linked to lateral root (LR) formation and is essential for regular LR spacing along the primary root. However, it remains unclear how this internal mechanism is influenced by environmental factors known to affect the LR pattern. Here, we report that excessive cadmium (Cd) inhibits LR formation by disrupting the lateral root cap (LRC)-programmed cell death (PCD)-regulated root clock. Cd restricts the frequency of the oscillating signal rather than its amplitude. This could be attributed to the inhibition on meristematic activity by Cd, which resulted in decreased LRC cell number and LRC-PCD frequency. Genetic evidence further showed that LRC cell number is positively correlated with root resistance to Cd. Our study reveals root cap dynamics as a novel mechanism mediating root responses to Cd, providing insight into the signalling pathways of the root clock responding to environmental cues.

The dynamic nature and regulation of the root clock

“…In addition to the endogenous signaling network, environmental factors are able to influence lateral root formation but at different developmental steps. A recent study suggests that excessive exposure to the heavy metal cadmium inhibits pre-branch site formation through the repression of periodic LRC-PCD and DR5 oscillations (Xie et al, 2019). In Arabidopsis, heterogeneous distribution of nutrients in the soil, such as phosphate and nitrogen, also largely influence the primary root and LR development through moderating auxin signaling, transport and cell cycle progression (Guan et al, 2017;Lima et al, 2010;O'Brien et al, 2016;Perez-Torres et al, 2008).…”

Volatile compounds from beneficial rhizobacteria Bacillus spp. promote periodic lateral root development in Arabidopsis

“…Environmental factors can affect different LR development stages (Motte, Vanneste, & Beeckman, 2019). Light, heavy metal cadmium and water deficit have been recently reported to affect LR formation through modulating DR5:Luciferase expression in OZ and to affect the subsequent prebranch site formation (Kircher & Schopfer, 2018;Orman-Ligeza et al, 2018;Xie et al, 2019). Beneficial rhizosphere microorganisms can dramatically affect root development by facilitating root cell division and differentiation (Lopez-Bucio et al, 2007;Ortiz-Castro, Martinez-Trujillo, & Lopez-Bucio, 2008;Ortiz-Castro, Valencia-Cantero, & Lopez-Bucio, 2008;Patten & Glick, 2002;Zamioudis, Mastranesti, Dhonukshe, Blilou, & Pieterse, 2013;Zou, Li, & Yu, 2010;Zuniga et al, 2013).…”

A novel petal up-regulated <i>PhXTH7</i> promoter analysis in <i>Petunia hybrida</i> by using bioluminescence reporter gene

“…This fast response luminescent system does not require any excitation light like fluorescent proteins, and signal detection is much faster and less destructive in comparison to the GUS assay. One disadvantage of the bioluminescence emitted from the conventional Fluc, however, is the dim luminescence that limits the spatial resolution of imaging (Xie et al 2019). In 2016, Green enhanced Nano-Lantern (GeNL), a novel bioluminescent protein was developed allowing bioimaging with high spatiotemporal resolution in mammalian cells (Suzuki et al 2016).…”