Dynamic infrared imaging analysis of apical hook development in Arabidopsis: the case of brassinosteroids

Abstract

SummaryGermination of Arabidopsis seeds in darkness induces apical hook development, based on a tightly regulated differential growth coordinated by a multiple hormone cross-talk. Here, we endeavoured to clarify the function of brassinosteroids (BRs) and cross-talk with ethylene in hook development.An automated infrared imaging system was developed to study the kinetics of hook development in etiolated Arabidopsis seedlings. To ascertain the photomorphogenic control of hook opening, the system was equipped with an automatic light dimmer.We demonstrate that ethylene and BRs are indispensable for hook formation and maintenance. Ethylene regulation of hook formation functions partly through BRs, with BR feedback inhibition of ethylene action. Conversely, BR-mediated extension of hook maintenance functions partly through ethylene. Furthermore, we revealed that a short light pulse is sufficient to induce rapid hook opening.Our dynamic infrared imaging system allows high-resolution, kinetic imaging of up to 112 seedlings in a single experimental run. At this high throughput, it is ideally suited to rapidly gain insight in pathway networks. We demonstrate that BRs and ethylene cooperatively regulate apical hook development in a phase-dependent manner. Furthermore, we show that light is a predominant regulator of hook opening, inhibiting ethylene-and BR-mediated postponement of hook opening.

Light Controls Cytokinin Signaling via Transcriptional Regulation of Constitutively Active Sensor Histidine Kinase CKI1

“…Hook formation, and its opening, was previously demonstrated to be under hormonal and light control (Vriezen et al, 2004;Zádniková et al, 2010;Smet et al, 2014). Considering that, we investigated the potential impact of hy1-7 and phyA on the CKI1 expression during hook development and real-time kinetics of individual stages of the process, i.e.…”

Ethylene and Hormonal Cross Talk in Vegetative Growth and Development

“…The constitutive ethylene response mutant ctr1 exhibits an exaggerated hook in the absence of ethylene (Abbas et al, 2013;Mazzella et al, 2014). Apical hook development is deficient in the ethylene-insensitive mutant ein2 (Guzmán and Ecker, 1990), resulting from a severe inhibition of apical hook formation (Smet et al, 2014). Similarly, loss of function of the transcription factor EIN3 results in a reduced curvature, whereas EIN3 overexpression induces an enhanced apical hook curvature (An et al, 2012a).…”

“…Both hormones promote hook formation and prevent hook opening ( Fig. 1; Vandenbussche et al, 2010;Zádníková et al, 2010;Gallego-Bartolomé et al, 2011;Smet et al, 2014). GA biosynthesis is indispensable for apical hook formation and the ethylene-induced apical hook exaggeration (Gallego-Bartolomé et al, 2011;An et al, 2012a), and ethylene promotes GA biosynthesis in the apical hook (Mazzella et al, 2014).…”

“…Ethylene also regulates the transition between hook maintenance and opening by preventing hook opening ( Fig. 1; Vandenbussche et al, 2010;Gallego-Bartolomé et al, 2011;Smet et al, 2014). Ethylene biosynthesis, perception, and signaling are indispensable for a flawless development of the apical hook.…”

“…The expression of the auxin influx carriers AUXIN RESISTANT1 (AUX1)/LIKE AUXIN RESISTANCE3 and the auxin efflux carrier PIN-FORMED3 (PIN3) was enhanced, while that of PIN1 and PIN4 was reduced, by ethylene Zádníková et al, 2010). BR, GA, and JA also impinge on auxin biosynthesis, transport, and signaling in the regulation of auxin distribution in the apical hook, whether or not through ethylene (De Grauwe et al, 2005;Gallego-Bartolomé et al, 2011;An et al, 2012a;Smet et al, 2014;Zhang et al, 2014b).…”