Autophagy—an underestimated coordinator of construction and destruction during plant root ontogeny

Abstract

Main Conclusion Autophagy is a key but undervalued process in root ontogeny, ensuring both the proper development of root tissues as well as the senescence of the entire organ. Abstract Autophagy is a process which occurs during plant adaptation to changing environmental conditions as well as during plant ontogeny. Autophagy is also engaged in plant root development, however, the limitations of belowground studies make it challenging to understand the entirety of the developmental processes. We summarize and discuss the current data pertaining to autophagy in the roots of higher plants during their formation and degradation, from the beginning of root tissue differentiation and maturation; all the way to the aging of the entire organ. During root growth, autophagy participates in the processes of central vacuole formation in cortical tissue development, as well as vascular tissue differentiation and root senescence. At present, several key issues are still not entirely understood and remain to be addressed in future studies. The major challenge lies in the portrayal of the mechanisms of autophagy on subcellular events in belowground plant organs during the programmed control of cellular degradation pathways in roots. Given the wide range of technical areas of inquiry where root-related research can be applied, including cutting-edge cell biological methods to track, sort and screen cells from different root tissues and zones of growth, the identification of several lines of evidence pertaining to autophagy during root developmental processes is the most urgent challenge. Consequently, a substantial effort must be made to ensure whether the analyzed process is autophagy-dependent or not.

Autophagy in the Lifetime of Plants: From Seed to Seed

“…Structurally, plant roots are divided into three zones: the meristematic zone, elongation zone, and maturation zone [ 20 ]. A cross-section of roots includes three levels: dermal, cortex (ground tissue), and vascular tissues [ 21 ]. During root development, autophagy plays an important role in its establishment and functional differentiation.…”

“…ATG8 genes are mainly located in the root caps and maturation zone, which correspond to relevant protein degradation [ 22 ]. The role of autophagy in the root tips may be related to programmed cell death (PCD), but there is not enough evidence to prove this speculation [ 21 ].…”

“…In roots, xylem formation occurs primarily via nitric oxide (NO) signaling, through the synthesis of secondary cell walls and degradation of protoplast [ 24 ]. Autophagy-related processes appear to play a role in central vacuole formation and the degradation of cytoplasmic material at the onset of xylem partialization [ 21 ]. Several ATG genes ( ATG8C , ATG8D , ATG11 , and ATG18 ) are certified in the differentiation of the xylem [ 25 ].…”

“…The up-regulation of ATG genes ( ATG8C , ATG8D , and ATG8G ) is characterized by the senescence of absorptive roots [ 26 ]. During the first stage of senescence, autophagy counteracts transient cell death and maintains cellular homeostasis [ 21 ]. Additionally, autophagy is also involved in the remobilization process, which is a key step in the senescence process [ 21 ].…”

“…During the first stage of senescence, autophagy counteracts transient cell death and maintains cellular homeostasis [ 21 ]. Additionally, autophagy is also involved in the remobilization process, which is a key step in the senescence process [ 21 ].…”