The E3 SUMO ligase AtSIZ1 functions in seed germination in Arabidopsis

Abstract

Seed germination is an important stage in the lifecycle of a plant because it determines subsequent vegetative growth and reproduction. Here, we show that the E3 SUMO ligase AtSIZ1 regulates seed dormancy and germination. The germination rates of the siz1 mutants were less than 50%, even after a short period of ripening. However, their germination rates increased to wild-type levels after cold stratification or long periods of ripening. In addition, exogenous gibberellin (GA) application improved the germination rates of the siz1 mutants to the wild-type level. In transgenic plants, suppression of AtSIZ1 caused rapid post-translational decay of SLEEPY1 (SLY1), a positive regulator of GA signaling, during germination, and inducible AtSIZ1 overexpression led to increased SLY1 levels. In addition, overexpressing wild-type SLY1 in transgenic sly1 mutants increased their germination ratios to wild-type levels, whereas the germination ratio of transgenic sly1 mutants overexpressing mSLY1 was similar to that of sly1. The germination ratios of siz1 mutant seeds in immature developing siliques were much lower than those of the wild-type. Moreover, SLY1 and DELAY OF GERMINATION 1 (DOG1) transcript levels were reduced in the siz1 mutants, whereas the transcript levels of DELLA and ABSCISIC ACID INSENSITIVE 3 (ABI3) were higher than those of the wild-type. Taken together, these results indicate that the reduced germination of the siz1 mutants results from impaired GA signaling due to low SLY1 levels and activity, as well as hyperdormancy due to high levels of expression of dormancy-related genes including DOG1.

Post‐translational modifications of Arabidopsis E3 SUMO ligase AtSIZ1 are controlled by environmental conditions

“…Therefore, the current data strongly suggest that sumoylation activates and stabilizes AtSIZ1 under drought stress. Previous studies also observed sumoylation of several proteins in response to drought . Our data suggest that AtSIZ1 participates in the sumoylation of target proteins in response to drought stress, working independently or together with other E3 SUMO ligases.…”

“…Plant E3 SUMO ligases are involved in responding to abiotic stresses, such as cold, drought, heat, and salt , and also have roles in various development processes . Recent studies showed that the activity and stability of Arabidopsis E3 SUMO ligase AtSIZ1 were regulated by COP1 activity .…”

“…SAF‐A/B‐Acinus‐PIAS (SAP)and Miz‐finger domain‐containing protein 1 (SIZ1) is an E3 SUMO ligase that has a RING‐like domain, Siz‐PIAS RING (SP‐RING), and a chromatin organization domain, SAP . Arabidopsis E3 SUMO ligase is involved in several developmental processes including germination, nutrient assimilation, hormone signaling, and flowering . In addition, plant E3 SUMO ligases have important roles in the responses to abiotic stresses such as low temperature, drought, heat, and high salt .…”

Exploiting protein modification systems to boost crop productivity: SUMO proteases in focus

“…Both the siz1 and the ots1ots2 double mutant exhibit a late germination phenotype (Castro et al , 2016; Kim et al , 2016) and abscisic acid hypersensitivity (Miura and Hasegawa, 2010), while SUMO overexpression leads to abscisic acid hyposensitivity (Lois et al , 2003). …”

APETALA 2‐domain‐containing transcription factors: focusing on abscisic acid and gibberellins antagonism

“…During seed germination, the small ubiquitin‐like modifier (SUMO) E3 ligase SIZ1 attenuates ABA signaling through sumoylation of ABSCISIC ACID INSENSITIVE 5 (ABI5), an important positive regulator of ABA signaling (Miura et al ., ). However, a recent study showed that SIZ1 also impairs GA signaling during seed germination by promoting the degradation of SLEEPY (SLY1), a positive regulator of GA signaling (Kim et al ., ), so it is likely that SIZ1 exhibits a negative effect on both ABA and GA signaling. Furthermore, the rice SnRK2‐APC/C Tiller Enhancer (OsTE) ubiquitin E3 complex regulatory module might represent another regulatory hub in ABA–GA antagonism, in which OsTE physically interacts with the ABA receptors OsPYLs/OsRCARs and promotes their degradation by the 26S‐mediated proteasome pathway, while GAs decrease the level of SnRK2s and may promote APC/C TE ‐mediated degradation of OsPYL/OsRCARs (Lin et al ., ).…”