Constitutive expression of the Zea mays L. (maize) morphogenic transcription factors Baby Boom (Bbm) and Wuschel2 (Wus2) in maize can not only greatly increase transformation efficiency but can also induce phenotypic abnormalities and sterility. In an effort to alleviate the pleiotropic effects of constitutive expression, a genome wide search was undertaken to find suitable maize promoters to drive tissue and timing-specific expression of the transformation enhancing genes Bbm and Wus2. A promoter from a maize phospholipid transferase protein gene (Zm-PLTPpro ) was identified based on its expression in leaves, embryos, and callus while being downregulated in roots, meristems, and reproductive tissues. When Zm-PLTPpro driving Bbm was transformed into immature maize embryos along with a Wus2 expression cassette driven by the nopaline synthase promoter (Nospro ::Wus2) abundant somatic embryos rapidly formed on the scutella. These embryos were individual and uniformly transformed and could be directly germinated into plants without a callus phase. Transformed plants could be sent to the greenhouse in as little as 1 mo and regenerated plants matched the seed-derived phenotype for the inbred and were fertile. However, T1 seed from these plants had poor germination. Replacing Nospro with a maize auxin-inducible promoter (Zm-Axig1pro ) in combination with Zm-PLTPpro ::Bbm, allowed healthy, fertile plants to be regenerated. Single-copy T1 seed germinated normally and had a predominantly wild-type inbred phenotype. For maize, this callus-free transformation process has worked in all inbred lines tested.

中文翻译：

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通过直接的体细胞胚发生快速基因型“独立”的玉米（玉米）转化。

玉米（Zea mays L.）形态发生转录因子Baby Boom（Bbm）和Wuschel2（Wus2）在玉米中的组成性表达不仅可以大大提高转化效率，而且还可以诱导表型异常和不育。为了减轻组成型表达的多效性作用，进行了全基因组搜索以找到合适的玉米启动子来驱动转化增强基因Bbm和Wus2的组织和时间特异性表达。根据玉米磷脂转移酶蛋白基因（Zm-PLTPpro）在叶，胚和愈伤组织中的表达而在根，分生组织和生殖组织中下调的表达确定了其启动子。当由Zm-PLTPpro驱动的Bbm与由胭脂碱合酶启动子（Nospro :: Wus2）驱动的Wus2表达盒一起转化为未成熟的玉米胚时，在the子上迅速形成了丰富的体细胞胚。这些胚是单个的并且被均匀地转化，并且可以被直接发芽成没有愈伤组织阶段的植物。转化的植物可以在短短的1个月内送入温室，再生的植物与近交种子的种子表型相匹配，并且能育。但是，这些植物的T1种子发芽较差。用玉米生长素诱导型启动子（Zm-Axig1pro）结合Zm-PLTPpro :: Bbm替代Nospro，可以再生健康，可育的植物。单拷贝T1种子正常发芽，并具有野生型近交表型。对于玉米