Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA.
BMC Plant Biol. 2012 Nov 13;12:214. doi: 10.1186/1471-2229-12-214.
The INNER NO OUTER (INO) gene, which encodes a YABBY-type transcription factor, specifies and promotes the growth of the outer integument of the ovule in Arabidopsis. INO expression is limited to the abaxial cell layer of the developing outer integument of the ovule and is regulated by multiple regions of the INO promoter, including POS9, a positive element that when present in quadruplicate can produce low-level expression in the normal INO pattern.
Significant redundancy in activity between different regions of the INO promoter is demonstrated. For specific regulatory elements, multimerization or the addition of the cauliflower mosaic virus 35S general enhancer was able to activate expression of reporter gene constructs that were otherwise incapable of expression on their own. A new promoter element, POS6, is defined and is shown to include sufficient positive regulatory information to reproduce the endogenous pattern of expression in ovules, but other promoter regions are necessary to fully suppress expression outside of ovules. The full-length INO promoter, but not any of the INO promoter deletions tested, is able to act as an enhancer-blocking insulator to prevent the ectopic activation of expression by the 35S enhancer. Sequence conservation between the promoter regions of Arabidopsis thaliana, Brassica oleracea and Brassica rapa aligns closely with the functional definition of the POS6 and POS9 regions, and with a defined INO minimal promoter. The B. oleracea INO promoter is sufficient to promote a similar pattern and level of reporter gene expression in Arabidopsis to that observed for the Arabidopsis promoter.
At least two independent regions of the INO promoter contain sufficient regulatory information to direct the specific pattern but not the level of INO gene expression. These regulatory regions act in a partially redundant manner to promote the expression in a specific pattern in the ovule and suppress expression outside of ovules. Establishment of this pattern requires cooperation and competition between multiple positive and negative regulatory elements.
INO 基因（编码 YABBY 型转录因子）编码一个 YABBY 型转录因子，指定并促进拟南芥胚珠外珠被的生长。INO 表达仅限于胚珠外珠被的背侧细胞层，受 INO 启动子的多个区域调控，包括 POS9，一个正元件，当其存在四倍时，可以在正常 INO 模式下产生低水平表达。
证明了 INO 启动子不同区域之间存在显著的活性冗余。对于特定的调节元件，多聚化或添加花椰菜花叶病毒 35S 通用增强子能够激活自身无法表达的报告基因构建体的表达。定义了一个新的启动子元件 POS6，并表明它包含足够的正调控信息来重现胚珠中内源性表达模式，但其他启动子区域是完全抑制胚珠外表达所必需的。全长 INO 启动子，但不是测试的任何 INO 启动子缺失，能够作为增强子阻断绝缘子，防止 35S 增强子的异位激活表达。拟南芥、甘蓝和油菜的启动子区域之间的序列保守性与 POS6 和 POS9 区域的功能定义以及定义的 INO 最小启动子紧密一致。甘蓝 INO 启动子足以在拟南芥中促进类似的报告基因表达模式和水平，与观察到的拟南芥启动子相似。
INO 启动子的至少两个独立区域包含足够的调节信息来指导 INO 基因表达的特定模式，但不是表达水平。这些调节区域以部分冗余的方式起作用，以在胚珠中促进特定模式的表达，并抑制胚珠外的表达。建立这种模式需要多个正调控和负调控元件之间的合作和竞争。
