Molecular and physiological control of adventitious rooting in cuttings: phytohormone action meets resource allocation

Abstract

Background Adventitious root (AR) formation in excised plant parts is a bottleneck for survival of isolated plant fragments. AR formation plays an important ecological role and is a critical process in cuttings for the clonal propagation of horticultural and forestry crops. Therefore, understanding the regulation of excision-induced AR formation is essential for sustainable and efficient utilization of plant genetic resources. Scope Recent studies of plant transcriptomes, proteomes and metabolomes, and the use of mutants and transgenic lines have significantly expanded our knowledge concerning excision-induced AR formation. Here, we integrate new findings regarding AR formation in the cuttings of diverse plant species. These findings support a new system-oriented concept that the phytohormone-controlled reprogramming and differentiation of particular responsive cells in the cutting base interacts with a co-ordinated reallocation of plant resources within the whole cutting to initiate and drive excision-induced AR formation. Master control by auxin involves diverse transcription factors and mechanically sensitive microtubules, and is further linked to ethylene, jasmonates, cytokinins and strigolactones. Hormone functions seem to involve epigenetic factors and cross-talk with metabolic signals, reflecting the nutrient status of the cutting. By affecting distinct physiological units in the cutting, environmental factors such as light, nitrogen and iron modify the implementation of the genetically controlled root developmental programme. Conclusion Despite advanced research in the last decade, important questions remain open for future investigations on excision-induced AR formation. These concern the distinct roles and interactions of certain molecular, hormonal and metabolic factors, as well as the functional equilibrium of the whole cutting in a complex environment. Starting from model plants, cell type- and phase-specific monitoring of controlling processes and modification of gene expression are promising methodologies that, however, need to be integrated into a coherent model of the whole system, before research findings can be translated to other crops.

Gene expression profiling reveals light regulation on adventitious root formation in lotus (Nelumbo nucifera Gaertn.)

“…The seedling under darkness condition could not form ARs, and high light intensity promoted the developmental process of ARs (Fig.1, Table.1). Interaction of light with other factors is found to be cooperatively involved in root development [44]. Light regulating ARs development often derives from sucrose content of photosynthate, and this effect mainly reflected on root number [45,46].…”

The Roles of Auxin Biosynthesis YUCCA Gene Family in Plants

“…Numerous studies have demonstrated that early auxin accumulation is a critical signal to initiate cell fate transition of the root founder cells, which is essential for vegetative propagation of plants [104][105][106]. This auxin peak was the combined outcome of PAT and increased local synthesis in response to multiple exogenous stimuli such as wounding and depletion of water and nutrient [107,108]. It is demonstrated that YUC gene family orchestrated endogenous auxin biosynthesis required for AR induction, among which YUC1 and 4 appeared to play the most important role [28,109].…”

Understanding of Adventitious Root Formation: What Can We Learn From Comparative Genetics?

“…We previously discussed about the contribution of genetic variation approaches for the molecular understanding of excision-induced AR formation in stem cuttings of important woody species such as poplar, Eucalyptus spp., and olive trees ( Druege et al, 2019 ). In Arabidopsis, excised leaf explants are able to produce ARs from some vascular associated cells ( Liu et al, 2014 ; Bustillo-Avendaño et al, 2018 ), and recent genetic studies have identified several key regulators that are involved in this process ( Jing et al, 2020 ).…”

“…In many dicots, however, the postembryonic root system is mainly composed of lateral roots (LRs), which originate from the pericycle cell layer of already formed roots ( Dubrovsky et al, 2006 ; Péret et al, 2009 ). In these species, ARs are also formed, mainly in response to specific stress signals, such as waterlogging and wounding, the latter being usually applied during stem cutting propagation ( Druege et al, 2019 ).…”