背景回顾：The genetic distance between hybridizing parents affects heterosis; however, the mechanisms for this remain unclear. 

主要发现：Here we report that this genetic distance correlates with natural variation and epigenetic regulation of circadian clock-mediated stress responses. 

结果1-杂种中胁迫响应基因被抑制：In intraspecific hybrids of Arabidopsis thaliana, genome-wide expression of many biotic and abiotic stress-responsive genes is diurnally repressed and this correlates with biomass heterosis and biomass quantitative trait loci.

结果2-胁迫响应与生长的平衡： Expression differences of selected stress-responsive genes among diverse ecotypes are predictive of heterosis in their hybrids. Stress-responsive genes are repressed in the hybrids under normal conditions but are induced to mid-parent or higher levels under stress at certain times of the day, potentially balancing the tradeoff between stress responses and growth. 

结果3-实验验证：Consistent with this hypothesis, repression of two candidate stress-responsive genes increases growth vigour. 

结论：Our findings may therefore provide new criteria for effectively selecting parents to produce high- or low-yield hybrids.

 摘 要 

杂交亲本之间的遗传距离会影响杂种优势；但是，该现象的分子机制仍不清楚。本文中，作者发现这种遗传距离与生物钟介导的胁迫响应的自然变异和表观调控有关。在拟南芥的种间杂种中，很多生物和非生物胁迫响应基因的表达在日间是被抑制的，并且这与生物量杂种优势以及生物量数量性状位点相关。不同生态型之间胁迫响应基因的表达差异能够预测其杂交种的杂种优势。杂种中的胁迫响应基因在正常条件下会被抑制，但是在胁迫时会在一天的某个时间段诱导至亲本中间型或者更高水平，可能在胁迫响应和生长之间保持了平衡。与该假设一致，抑制两个候选的胁迫响应基因能够增强生长优势。本文的发现为有效选择亲本组合来创制高产或低产杂种提供参考。

 Z. Jeffrey Chen