Sheehan Moira J, Farmer Phyllis R, Brutnell Thomas P
Boyce Thompson Institute, Cornell University, Ithaca, New York 14853, USA.
Genetics. 2004 Jul;167(3):1395-405. doi: 10.1534/genetics.103.026096.
To begin the study of phytochrome signaling in maize, we have cloned and characterized the phytochrome gene family from the inbred B73. Through DNA gel blot analysis of maize genomic DNA and BAC library screens, we show that the PhyA, PhyB, and PhyC genes are each duplicated once in the genome of maize. Each gene pair was positioned to homeologous regions of the genome using recombinant inbred mapping populations. These results strongly suggest that the duplication of the phytochrome gene family in maize arose as a consequence of an ancient tetraploidization in the maize ancestral lineage. Furthermore, sequencing of Phy genes directly from BAC clones indicates that there are six functional phytochrome genes in maize. Through Northern gel blot analysis and a semiquantitative reverse transcriptase polymerase chain reaction assay, we determined that all six phytochrome genes are transcribed in several seedling tissues. However, expression from PhyA1, PhyB1, and PhyC1 predominate in all seedling tissues examined. Dark-grown seedlings express higher levels of PhyA and PhyB than do light-grown plants but PhyC genes are expressed at similar levels under light and dark growth conditions. These results are discussed in relation to phytochrome gene regulation in model eudicots and monocots and in light of current genome sequencing efforts in maize.
为了开展玉米中光敏色素信号传导的研究，我们从自交系B73中克隆并鉴定了光敏色素基因家族。通过对玉米基因组DNA进行DNA凝胶印迹分析以及筛选BAC文库，我们发现PhyA、PhyB和PhyC基因在玉米基因组中均各自复制了一次。利用重组自交系作图群体，将每对基因定位到基因组的同源区域。这些结果有力地表明，玉米中光敏色素基因家族的复制是玉米祖先谱系中一次古老的四倍体化的结果。此外，直接从BAC克隆对Phy基因进行测序表明，玉米中有六个功能性光敏色素基因。通过Northern凝胶印迹分析和半定量逆转录聚合酶链反应检测，我们确定所有六个光敏色素基因在几种幼苗组织中均有转录。然而，在所有检测的幼苗组织中，PhyA1、PhyB1和PhyC1的表达占主导。黑暗中生长的幼苗比光照下生长的植物表达更高水平的PhyA和PhyB，但PhyC基因在光照和黑暗生长条件下的表达水平相似。结合模式双子叶植物和单子叶植物中光敏色素基因的调控以及当前玉米基因组测序工作，对这些结果进行了讨论。
