背景回顾：The sheathing leaf found in grasses and other monocots is an evolutionary innovation, yet its origin has been a subject of long-standing debate. 

主要研究：Here, we revisit the problem in the light of developmental genetics and computational modeling.

结果：We show that the sheathing leaf likely arose through WOX-gene-dependent extension of a primordial zone straddling concentric domains around the shoot apex. Patterned growth within this zone, oriented by two polarity fields, accounts for wild-type, mutant and mosaic grass leaf development, whereas zone contraction and growth remodeling accounts for eudicot leaf development. 

结论：In contrast to the prevailing view, our results suggest that the sheath derives from petiole, whereas the blade derives from the lamina of the eudicot leaf, consistent with homologies proposed in the 19th century.

 摘 要 

在禾本科植物和其它单子叶植物中发现的鞘叶是一种演化创新，但其起源一直是一个长期争论的话题。本文中，作者从发育遗传学和计算机建模的角度重新审视这个问题。作者的研究发现，鞘叶可能是通过依赖于WOX基因的原生区（primordial zone，PZ）延伸所产生的，PZ延伸后环抱了茎尖区的同心域。该区域内受到两个极性场决定方向的模式生长解释了野生型、突变体以及马赛克的禾本科植物叶发育，而该区域的收缩和生长重塑则解释了双子叶植物的叶发育。与主流的观点相反，作者的研究结果显示单子叶植物的鞘叶源自于叶柄，而叶片则源自于真双子叶植物叶的叶片，这与19世纪提出的叶柄-叶鞘同源假说一致。