Abstract
Plants depend on gravity to provide the constant landmark for downward root growth and upward shoot growth. The phytohormone auxin and its cell‐to‐cell transport machinery are central determinants ensuring gravitropic growth. Statolith sedimentation toward gravity is sensed in specialized cells. This positional cue is translated into the polar distribution of PIN auxin efflux carriers at the plasma membrane, leading to asymmetric auxin distribution and consequently, differential growth and organ bending. While we have started to understand the general principles of how primary organs execute gravitropism, we currently lack basic understanding of how lateral plant organs can defy gravitropic responses. Here we briefly review the establishment of the oblique gravitropic set point angle in lateral roots and particularly discuss the emerging role of asymmetric cytokinin signaling as a central anti‐gravitropic signal. Differential cytokinin signaling is co‐opted in gravitropic lateral and hydrotropic primary roots to counterbalance gravitropic root growth.
Highlights
In contrast to primary roots, lateral roots partially repress gravitropic growth and establish a distinct gravitropic set point angle (GSA; Digby and Firn 1995)
While PIN7 is transcriptionally repressed, PIN4 shows a post‐translational downregulation in stage II columella cells (Rosquete et al 2013), which might relate to reduced exocyst‐dependent trafficking to the plasma membrane
Delivery of PIN4 to the plasma membrane depends on EXOCYST70A3 (EXO70A3), and an increase in PIN4 exocytosis in columella cells leads to more gravitropic growth (Ogura et al 2019)
Summary
In contrast to primary roots, lateral roots partially repress gravitropic growth and establish a distinct gravitropic set point angle (GSA; Digby and Firn 1995). The expression of PIN3 is only transient and its repression in stage III lateral roots correlates with non‐differential growth (Figure 1) and, maintenance of GSA in these lateral organs (Guyomarc'h et al 2012; Rosquete et al 2013, 2018).
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
