WHIRLY proteins maintain seed viability and regulate plant development

The WHIRLY (WHY) family of DNA/RNA binding proteins fulfil multiple functions in plants but their functions in seed viability, germination and plant development remain poorly characterised. We therefore analysed these processes in the Atwhy1, Atwhy3 and Atwhy1why3 double mutants compared to the wild type controls. While germination was similar in the unaged high quality seeds of all lines, significant decreases in vigour and viability were observed in the aged mutant seeds compared to the wild type. Moreover, the Atwhy1, Atwhy3 and Atwhy1why3 mutants had reduced rosette biomass, with a smaller average leaf area and fewer leaves that the wild type at 6 weeks. The Atwhy3 and Atwhy1why3 double mutants showed a significant delay in flowering, having more siliques per plant but with fewer seeds per silique than the wild type. RNA-seq profiling of the Atwhy1why3 mutant seeds relative to the wild type revealed changes in the levels of transcripts encoding heat shock response proteins (HSP), and the APETALA2 (AP2) transcription factor, ERF112, and the vernalisation gene VRN3/FT that explain the seed and shoot phenotypes of the plants lacking WHY proteins. There was no evidence of WHY-mediated effects on the expression of DNA repair or antioxidant response proteins suggesting that the absence of WHY proteins did not lead to accumulated DNA damage in aging seeds. We conclude that WHY1 and WHY3 determine the vigour of Arabidopsis seeds and protect germination under conditions of accelerated ageing stress.