The evolution of multicellularity is a premier example of phenotypic convergence: simple multicellularity evolved independently many times, and complex multicellular phenotypes are found in several distant groups. Furthermore, both animal and plant lineages have independently reached extreme levels of morphological, functional, and developmental complexity. This study explores the genetic basis for the parallel evolution of complex multicellularity and development in the animal and green plant (i.e., green algae and land plants) lineages. Specifically, the study (i) identifies the SAND domain—a DNA-binding domain with important roles in the regulation of cell proliferation and differentiation, as unique to animals, green algae, and land plants; and (ii) suggests that the parallel deployment of this ancestral domain in similar regulatory roles could have contributed to the independent evolution of complex development in these distant groups. Given the deep animal-green plant divergence, the limited distribution of the SAND domain is best explained by invoking a lateral gene transfer (LGT) event from a green alga to an early metazoan. The presence of a sequence motif specifically shared by a family of SAND-containing transcription factors involved in the evolution of complex multicellularity in volvocine algae and two types of SAND proteins that emerged early in the evolution of animals is consistent with this scenario. Overall, these findings imply that (i) in addition to be involved in the evolution of similar phenotypes, deep homologous sequences can also contribute to shaping parallel evolutionary trajectories in distant lineages, and (ii) LGT could provide an additional source of latent homologous sequences that can be deployed in analogous roles and affect the evolutionary potentials of distantly related groups.

中文翻译：

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动植物复杂发育的独立进化：深层同源性和横向基因转移。

多细胞性的进化是表型融合的一个典型例子：简单的多细胞性独立地进化了许多次，并且在多个遥远的群体中发现了复杂的多细胞表型。此外，动植物谱系都已独立达到形态，功能和发育复杂性的极端水平。这项研究探索了动物和绿色植物（即，绿藻和陆地植物）谱系中复杂多细胞性的平行进化和发育的遗传基础。具体而言，研究（i）确定了SAND结构域-一种在细胞增殖和分化调控中起重要作用的DNA结合结构域，对动物，绿藻和陆地植物而言是独特的；（ii）建议在相似的监管角色中并行部署这个祖先域可能有助于这些遥远群体中复杂发展的独立演变。考虑到深绿色的动物-绿色植物的差异，最好通过调用从绿藻到后生动物的侧向基因转移（LGT）事件来最好地解释SAND域的有限分布。涉及序列的基序的存在是由涉及SVOL的藻类中复杂的多细胞性的进化所涉及的含SAND的转录因子家族和在动物进化早期出现的两种类型的SAND蛋白共同形成的，与这种情况一致。总体而言，这些发现暗示（i）除了参与相似表型的进化之外，