Physcomitrella MADS-box genes regulate water supply and sperm movement for fertilization

MIKC classic (MIKCC)-type MADS-box genes encode transcription factors that function in various developmental processes, including angiosperm floral organ identity. Phylogenetic analyses of the MIKCC-type MADS-box family, including genes from non-flowering plants, suggest that the increased numbers of these genes in flowering plants is related to their functional divergence; however, their precise functions in non-flowering plants and their evolution throughout land plant diversification are unknown. Here, we show that MIKCC-type MADS-box genes in the moss Physcomitrella patens (小立碗藓) function in two ways to enable fertilization. Analyses of protein localization, deletion mutants and overexpression lines of all six genes indicate that three MIKCC-type MADS-box genes redundantly regulate cell division and growth in the stems for appropriate external water conduction (水分输导), as well as the formation of sperm with motile flagella (能动的鞭毛). The former function appears to be maintained in the flowering plant lineage, while the latter was lost in accordance with the loss of sperm.

MIKCC类MADS-box基因编码的转录因子在不同发育阶段起作用，包括被子植物花器官特征决定。包含不开花植物在内的MIKCC类MADS-box基因家族进化分析显示 该类基因数量的增加与其功能分化相关，然而，这类基因在非开花植物中的功能以及在整个陆地植物中的分化还知之甚少。本文的研究表明MIKCC类MADS-box基因在小立碗藓中通过两个方面的功能来保证受精作用。通过蛋白质定位、删除突变及过表达株系的研究，作者发现有三个MIKCC类MADS-box基因存在功能冗余，主要调控茎在响应外部水分输导师时的细胞分裂和生长，另外一方面还调控带有能动鞭毛的精子的形成。前面的这个功能在开花植物中保留了下来，而后面的这个功能由于开花植物的精子不具鞭毛而丧失了。

通讯：Mitsuyasu Hasebe (http://www.nibb.ac.jp/en/sections/evolutionary_biology_and_biodiversity/hasebe/index.html)

研究方向：先前主要利用模式植物对一些经典的生物演化问题背后的遗传机理进行研究，比如通过花的发育。进来通过几个陆地植物包括裸子植物，蕨类植物，苔藓植物和轮藻的比较发现，小立碗藓是一个比较有潜力的植物，可以用于研究模式植物中没有的一些生物学特性。作者现在主要是在研究一些模式植物中没有很好研究的生物演化特征背后的遗传学机制，包括微管调节，多能干细胞的起始、维持和再生，仿生学，宿主对象改变等。

doi: 10.1038/s41477-017-0082-9