Transcriptional regulation of the SUMO system in Arabidopsis thaliana

Abstract

Posttranslational modifications provide an important mechanism for plants to adapt to changes in their environment. The Small Ubiquitin-like Modifier (SUMO) has been implicated in the plant response to a number of environmental stresses, such as temperature, drought and salinity stress.
Bio-informatic analysis showed that the deSUMOylation system in crop cereals is disproportionately elaborate when compared to that of the non-cultivated Brachypodium dystachon.
RT-qPCR was used to study the changes in transcription of deSUMOylating enzymes, SUMO paralog and SUMOylating enzymes in response to various causes of SUMO conjugate accumulation: SUMO overexpression, loss of the ULP SUMO proteases OTS1 and OTS2 and abiotic stress treatment.
In order to assess the impact of SUMO overexpression on transcription in the SUMO system, two transgenic lines were produced which overexpress SUMO1 to different levels. These lines were characterised phenotypically and were then used to confirm previous data concerning the implication of SUMO in abscisic acid signalling.
Very few overarching patterns were found in the transcriptional response of ULP SUMO protease family members, implying they have individual regulation patterns. Additionally, this study provides evidence that the commonly used deconjugase/maturase dichotomy model requires review.
In contrast, the genes which encode the SUMO paralogs SUMO1/2/3/5 show a clear downregulation pattern to a set level in response to both SUMO overexpression and abiotic stress. These downregulation responses interact with each other and occur in a dose-dependent manner. This study also provides preliminary evidence that SUMO4 and SUMO6, which are generally deemed to be pseudogenes, are in fact transcribed at low levels.
Transcriptional profiling of the genes encoding SUMOylation enzymes yielded a variety of patterns. Remarkably, NaCl treatment led to the inversion of transcriptional dominance between the E3 ligases SIZ1 and HPY2. Finally, this study also uncovers a possible link between SUMOylation and deSUMOylation processes.