SUMO-Dependent Synergism Involving Heat Shock Transcription Factors with Functions Linked to Seed Longevity and Desiccation Tolerance.

Raúl Carranco,Concepción Almoguera,Juan Jordano,Pilar Prieto-Dapena

doi:10.3389/fpls.2017.00974

Abstract

A transcriptional synergism between HaHSFA9 (A9) and HaHSFA4a (A4a) contributes to determining longevity and desiccation tolerance of sunflower (Helianthus annuus, L.) seeds. Potential lysine SUMOylation sites were identified in A9 and A4a and mutated to arginine. We show that A9 is SUMOylated in planta at K38. Although we did not directly detect SUMOylated A4a in planta, we provide indirect evidence from transient expression experiments indicating that A4a is SUMOylated at K172. Different combinations of wild type and SUMOylation site mutants of A9 and A4a were analyzed by transient expression in sunflower embryos and leaves. Although most of the precedents in literature link SUMOylation with repression, the A9 and A4a synergism was fully abolished when the mutant forms for both factors were combined. However, the combination of mutant forms of A9 and A4a did not affect the nuclear retention of A4a by A9; therefore, the analyzed mutations would affect the synergism after the mutual interaction and nuclear co-localization of A9 and A4a. Our results suggest a role for HSF SUMOylation during late, zygotic, embryogenesis. The SUMOylation of A9 (or A4a) would allow a crucial, synergic, transcriptional effect that occurs in maturing sunflower seeds.

Highlights

The seed-specific heat-shock transcription factors (HSF) A9 and A4a function in enhancing longevity and desiccation tolerance of seeds (Prieto-Dapena et al, 2006, 2008; Personat et al, 2014)
The reported direct evidence for SUMOylation of A9 at K38 (Figure 1), and indirect evidence for SUMOylation of A4a at K172 (Figure 4B), adds these two HSFs to the -yet small- set of plant proteins that are known to be modified by small ubiquitin-like modifier (SUMO) (Budhiraja et al, 2009; Elrouby and Coupland, 2010; Miller et al, 2010, 2013; Lois, 2011; Castro et al, 2012; Elrouby et al, 2013; López-Torrejón et al, 2013; Park et al, 2011, 2013)
Precedent studies in animal systems showed that, in general, SUMOylation enhances the function of a variety of repressor complexes

Summary

Introduction

The seed-specific heat-shock transcription factors (HSF) A9 and A4a (respectively, Almoguera et al, 2002; Tejedor-Cano et al, 2014) function in enhancing longevity and desiccation tolerance of seeds (Prieto-Dapena et al, 2006, 2008; Personat et al, 2014). Among the specific effects of A9 and A4a, this pair of HSF synergically activates transcription from small Heat Shock Protein (sHSP) gene promoters (Tejedor-Cano et al, 2014). Transcriptional activation by A9 and A4a is repressed by the Aux/IAA protein HaIAA27 (Carranco et al, 2010; TejedorCano et al, 2014). This work indirectly indicated the contribution of additional -class A- HSFs, among them A4a as confirmed by subsequent work (Tejedor-Cano et al, 2010; Personat et al, 2014; Tejedor-Cano et al, 2014)

Methods

Results

Conclusion