背景回顾：Plant immunity frequently incurs growth penalties, which known as the trade-off between immunity and growth. Heterosis, the phenotypic superiority of a hybrid over its parents, has been demonstrated for many traits but rarely for disease resistance. 

主要研究：Here, we report that the central circadian oscillator, CCA1, confers heterosis for bacterial defense in hybrids without growth vigor costs, and it even significantly enhances the growth heterosis of hybrids under pathogen infection. 

结果1-CCA1生物学功能：The genetic perturbation of CCA1 abrogated heterosis for both defense and growth in hybrids. 

结果2-CCA1受到节律性调控：Upon pathogen attack, the expression of CCA1 in F1 hybrids is precisely modulated at different time points during the day by its rhythmic histone modifications. 

结果3-表观激活促进抗病：Before dawn of the first infection day, epigenetic activation of CCA1 promotes an elevation of salicylic acid accumulation in hybrids, enabling heterosis for defense. 

结果4-表观抑制促进生长：During the middle of every infection day, diurnal epigenetic repression of CCA1 leads to rhythmically increased chlorophyll synthesis and starch metabolism in hybrids, effectively eliminating the immunity-growth heterosis trade-offs in hybrids.

 摘 要 

植物免疫通常会以牺牲生长为代价，即在免疫和生长之间存在一个平衡。杂种优势，是杂交子代的表型优于双亲的现象，在许多表型性状中均已发现，但是有关抗病性方面的研究还比较少。本文中，作者报道了核心昼夜节律振荡器基因CCA1在不影响生长的情况下，赋予了杂种在细菌抗性方面的杂种优势，并且能够显著增强杂交种在病原菌侵染情况下的生长优势。遗传干扰CCA1会同时废除杂种在防御和生长方面的杂种优势。一旦病原菌侵染，在一天中不同的时间点，F1代杂种中CCA1的表达受到节律组蛋白修饰的精确调控。在第一天感染后、下一个黎明到来之前，CCA1基因的表观激活促进了水杨酸在杂种中的积累，从而实现了其在防御方面的杂种优势。而在病毒侵染后每一天的中午时分，CCA1基因的日表观抑制会导致杂交种叶绿素合成和淀粉代谢的节律性增加，从而有效地消除了杂交种中免疫和生长杂种优势之间的平。