背景回顾：The use of hybrids is widespread in agriculture, yet the molecular basis for hybrid vigor (heterosis) remains obscure. 

主要研究：To identify molecular components that may contribute to trait heterosis, we analyzed paired proteomic and transcriptomic data from seedling leaf and mature leaf blade tissues of maize hybrids and their inbred parents.

结果1-叶绿体和光合亚基：Nuclear- and plastid-encoded subunits of complexes required for protein synthesis in the chloroplast and for the light reactions of photosynthesis were expressed above midparent and high-parent levels, respectively. 

结果2-乙烯合成：Consistent with previous reports in Arabidopsis, ethylene biosynthetic enzymes were expressed below midparent levels in the hybrids, suggesting a conserved mechanism for heterosis between monocots and dicots. The ethylene biosynthesis mutant, acs2/acs6, largely phenocopied the hybrid proteome, indicating that a reduction in ethylene biosynthesis may mediate the differences between inbreds and their hybrids. 

结果3-株高杂种优势与质体核糖体蛋白水平：To rank the relevance of expression differences to trait heterosis, we compared seedling leaf protein levels to the adult plant height of 15 hybrids. Hybrid/midparent expression ratios were most positively correlated with hybrid/midparent plant height ratios for the chloroplast ribosomal proteins. 

结论：Our results show that increased expression of chloroplast ribosomal proteins in hybrid seedling leaves is mediated by reduced expression of ethylene biosynthetic enzymes and that the degree of their overexpression in seedlings can quantitatively predict adult trait heterosis.

 摘 要 

在农业中，杂种的利用十分普遍，但是杂种优势的分子基础还不是很清楚。为了鉴定那些可能作用于性状杂种优势的分子组分，作者分析了玉米杂种及其自交亲本的幼苗叶片和成熟叶片组织的蛋白组和转录组数据。作用于叶绿体蛋白合成的核编码和质体编码亚基在杂种中表达水平高于亲本的中值，而作用于光合作用的光反应亚基则高于亲本的最高值。与先前在拟南芥中报道的一致，乙烯生物合成酶在杂种中的表达要低于亲本的中值，说明在单子叶和双子叶植物中杂种优势存在保守的分子机制。乙烯合成突变体acs2/acs6的蛋白组与杂种的蛋白组高度相似，说明乙烯生物合成的减少可能是自交系和杂种之间差异的关键因素。为了进一步探讨表达差异与性状杂种优势之间的关联，作者比较了幼苗叶片蛋白水平与成年植株高度的相关性。叶绿体核糖体蛋白的杂种/亲本中值的表达比率与杂种/亲本中值的植株高度比率显著正相关。本文的研究结果显示杂种叶片中叶绿体核糖体蛋白的表达增加是由于乙烯生物合成酶的表达下调所导致的，并且其在幼苗中的过表达程度能够定量预测成年植株的性状杂种优势。