HRS1 Acts as a Negative Regulator of Abscisic Acid Signaling to Promote Timely Germination of Arabidopsis Seeds

Abstract

In this work, we conducted functional analysis of Arabidopsis HRS1 gene in order to provide new insights into the mechanisms governing seed germination. Compared with wild type (WT) control, HRS1 knockout mutant (hrs1-1) exhibited significant germination delays on either normal medium or those supplemented with abscisic acid (ABA) or sodium chloride (NaCl), with the magnitude of the delay being substantially larger on the latter media. The hypersensitivity of hrs1-1 germination to ABA and NaCl required ABI3, ABI4 and ABI5, and was aggravated in the double mutant hrs1-1abi1-2 and triple mutant hrs1-1hab1-1abi1-2, indicating that HRS1 acts as a negative regulator of ABA signaling during seed germination. Consistent with this notion, HRS1 expression was found in the embryo axis, and was regulated both temporally and spatially, during seed germination. Further analysis showed that the delay of hrs1-1 germination under normal conditions was associated with reduction in the elongation of the cells located in the lower hypocotyl (LH) and transition zone (TZ) of embryo axis. Interestingly, the germination rate of hrs1-1 was more severely reduced by the inhibitor of cell elongation, and more significantly decreased by the suppressors of plasmalemma H+-ATPase activity, than that of WT control. The plasmalemma H+-ATPase activity in the germinating seeds of hrs1-1 was substantially lower than that exhibited by WT control, and fusicoccin, an activator of this pump, corrected the transient germination delay of hrs1-1. Together, our data suggest that HRS1 may be needed for suppressing ABA signaling in germinating embryo axis, which promotes the timely germination of Arabidopsis seeds probably by facilitating the proper function of plasmalemma H+-ATPase and the efficient elongation of LH and TZ cells.

ABA inhibits myristoylation and induces shuttling of the RGLG1 E3 ligase to promote nuclear degradation of PP2CA

“…We examined the subcellular localization of RGLG1‐GFP in hypocotyl and root cells of Arabidopsis, where ABA signaling plays important roles, and which allows the easy identification of the cell nucleus by bright‐field microscopy (Wu et al ., ; Belda‐Palazon et al ., ). In hypocotyl cells, we found that RGLG1‐GFP was localized both in the plasma membrane and in the small vesicles found close to or associated with the plasma membrane (Figure a).…”

AtNIGT1/HRS1 integrates nitrate and phosphate signals at the Arabidopsis root tip

“…Finally, we believe that this transcriptomic analysis provides an important proxy towards understanding the other roles of HRS1 in plants. Indeed, it has been shown to be controlling germination 53 , or to confer drought or salt stress tolerance 54 . Again the general functions regulated by HRS1 such as “ROS signaling” as well the important overlap with ABA responsive genes are important keys to understand the underlying mechanisms behind the previously reported phenotypes.…”

HRS1/HHOs GARP transcription factors and reactive oxygen species are regulators of Arabidopsis nitrogen starvation response

“…The second factor found in this work, to be a strong regulators of NSR sentinel genes is HRS1. HRS1 was previously found to control the P response of primary root development Medici et al, 2015) and to control germination via an ABA dependent pathway (Wu et al, 2012). HRS1 and its close HHO homologous genes are also very well known to be among the most NO 3 regulated gene in the Arabidopsis genome (Canales et al, 2014;Krouk et al, 2010b;Wang et al, 2004).…”