Strigolactone and Cytokinin Act Antagonistically in Regulating Rice Mesocotyl Elongation in Darkness

Abstract

Strigolactones (SLs) are a group of phytohormones that control plant growth and development including shoot branching. Previous studies of the phenotypes of SL-related rice (Oryza sativa) dwarf (d) mutants demonstrated that SLs inhibit mesocotyl elongation by controlling cell division. Here, we found that the expression of cytokinin (CK)-responsive type-A RESPONSE REGULATOR (RR) genes was higher in d10-1 and d14-1 mutants than in the wild type. However, CK levels in mesocotyls of the d mutants were not very different from those in the wild type. On the other hand, application of a synthetic CK (kinetin) enhanced mesocotyl elongation in the d mutants and the wild type. d10-1 and d14-1 mesocotyls were more sensitive to CK than wild-type mesocotyls, suggesting that the up-regulation of the CK-responsive type-A RR genes and the higher elongation of mesocotyls in the d mutants are mainly due to the increased sensitivity of the d mutants to CK. Co-treatment with kinetin and a synthetic SL (GR24) confirmed the antagonistic functions of SL and CK on mesocotyl elongation. OsTCP5, which encodes a transcription factor belonging to the cell division-regulating TCP family, was also regulated by SL and CK and its expression was negatively correlated with mesocotyl length. These findings suggest that OsTCP5 contributes to the SL- and CK-controlled mesocotyl elongation in darkness.

Comparative phylogenomic analysis provides insights into TCP gene functions in Sorghum

“…Although nothing is known about OsTCP18 of rice, OsTCP5 has been shown to be regulated by strigalactones and cytokinins and is implicated in regulating mesocotyl length37. Arabidopsis orthologs ( AtTCP5, 13 and 17 ) of these genes regulate cell proliferation and differentiation during leaf development38.…”

TCP Transcription Factors at the Interface between Environmental Challenges and the Plant’s Growth Responses

“…The evidence for hormone involvement in TCP-mediated growth regulation accumulated in the recent years (Nicolas and Cubas, 2016). TCP functions have been associated with abscisic acid (Tatematsu et al, 2008; González-Grandío et al, 2013; Mukhopadhyay et al, 2015), auxin (Kosugi et al, 1995; Ben-Gera and Ori, 2012; Uberti-Manassero et al, 2012; Das Gupta et al, 2014), brassinosteroid (Guo et al, 2010), cytokinin (Steiner et al, 2012; Efroni et al, 2013), GA (Yanai et al, 2011; Das Gupta et al, 2014; Davière et al, 2014), jasmonic acid (Schommer et al, 2008; Danisman et al, 2012), salicylic acid (Wang X.et al, 2015), and strigolactone signaling pathways (Dun et al, 2012; Hu et al, 2014) ( Figure 2 ).…”

“…Here, Gh TCP3 acts in conjunction with DECREASED APICAL DOMINANCE 2, a receptor protein that normally inactivates strigolactones in response to decreased R:FR (Drummond et al, 2015). Rice OsTCP15 is involved in the mesocotyl elongation in response to darkness and responds to strigolactone and cytokinin treatments, outlining the interplay between TCPs and different plant hormones in developmental regulation that is responsive to the environment (Hu et al, 2014). …”

“… Schematic figure depicting the diversity of environmental signals that affect TCP functions in plants (Mukhtar et al, 2011; Sugio et al, 2011; Balsemão-Pires et al, 2013; González-Grandío et al, 2013; Niwa et al, 2013; Viola et al, 2013, 2016; Guan et al, 2014; Hu et al, 2014; Kim et al, 2014; Mukhopadhyay et al, 2015; Nicolas et al, 2015; Kumar et al, 2016) .…”

Mesocotyl elongation in Digitaria sanguinalis during seedling development

“…Mesocotyl elongation is a response to darkness, and it ceases when the tip of the coleoptile emerges into light (Robson et al 1988). In rice, Hu et al (2010Hu et al ( , 2014 have observed that the mesocotyl is highly elongated when seedlings are grown in darkness, whereas mesocotyl elongation is dramatically inhibited under light conditions. The growth of the mesocotyl is controlled by phytohormones.…”