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.

WHIRLY（WHY）家族DNA/RNA结合蛋白在植物中承担多种生物学功能，但其在种子活力、种子萌发及植株发育中的作用仍有待深入解析。为此，本研究以野生型植株为对照，对Atwhy1、Atwhy3及Atwhy1why3双突变体中的上述过程开展了分析。尽管所有株系的未老化优质种子萌发率相近，但老化后的突变体种子相较于野生型，其活力与存活力显著下降。此外，Atwhy1、Atwhy3及Atwhy1why3突变体的莲座生物量降低，在生长6周时，平均叶面积更小、叶片数量也少于野生型植株。Atwhy3与Atwhy1why3双突变体的开花时间显著延迟，单株结角果数更多，但每个角果内的种子数量却少于野生型。对Atwhy1why3突变体种子相较于野生型的转录组测序（RNA-seq）分析显示，编码热休克响应蛋白（heat shock response protein, HSP）、APETALA2（AP2）转录因子ERF112，以及春化基因VRN3/FT的转录本水平发生了变化，这一变化可解释WHY蛋白缺失植株的种子与地上部表型。未观察到WHY蛋白对DNA修复或抗氧化响应蛋白的表达产生介导性影响的证据，表明WHY蛋白的缺失并未导致老化种子中DNA损伤积累。综上，本研究表明WHY1与WHY3决定拟南芥种子的活力，并在加速老化胁迫下保障种子正常萌发。