Hollick J B, Patterson G I, Asmundsson I M, Chandler V L
Institute of Molecular Biology, University of Oregon, Eugene 97403-1229, USA.
Genetics. 2000 Apr;154(4):1827-38. doi: 10.1093/genetics/154.4.1827.
The maize purple plant (pl) locus encodes a transcription factor required for anthocyanin pigment synthesis in vegetative and floral tissues. The strongly expressed Pl-Rhoades (Pl-Rh) allele is unstable, spontaneously changing to weaker expression states (Pl') at low frequencies and exclusively changing to Pl' in Pl'/Pl-Rh heterozygotes. The weakly expressed Pl' state is mitotically and meiotically stable, yet reversible. This type of allele-dependent, heritable alteration of gene control is called paramutation. Expression studies herein demonstrate that visible differences in anthocyanin pigment levels mirror pl RNA abundance and that pl paramutation is associated with reduced transcription of the pl gene. This transcriptional alteration is accompanied by acquisition of light-dependent regulation. Restriction endonuclease mapping indicates that these changes in pl gene regulation are not associated with detectable DNA alterations or with extensive changes in cytosine methylation patterns. Genetic tests show that Pl-Blotched (Pl-Bh), a structurally similar pl allele encoding an identical pl RNA and PL protein, does not participate in pl paramutation. This result suggests that if cis-acting sequences are required for pl paramutation they are distinct from the protein coding and immediately adjacent regions. A model is discussed in which pl paramutation results in heritable changes of chromatin structure that fundamentally alter regulatory interactions occurring during plant development.
玉米紫色植株（pl）基因座编码一种在营养组织和花组织中花青素色素合成所需的转录因子。强表达的Pl-Rhoades（Pl-Rh）等位基因不稳定，会以低频率自发转变为较弱的表达状态（Pl'），并且在Pl'/Pl-Rh杂合子中只会转变为Pl'。弱表达的Pl'状态在有丝分裂和减数分裂过程中是稳定的，但可以逆转。这种依赖等位基因的、可遗传的基因调控改变被称为副突变。本文的表达研究表明，花青素色素水平的可见差异反映了pl RNA丰度，并且pl副突变与pl基因转录减少有关。这种转录改变伴随着光依赖性调控的获得。限制性内切酶图谱分析表明，pl基因调控的这些变化与可检测到的DNA改变或胞嘧啶甲基化模式的广泛变化无关。遗传测试表明，Pl-Blotched（Pl-Bh），一种结构相似的pl等位基因，编码相同的pl RNA和PL蛋白，不参与pl副突变。这一结果表明，如果pl副突变需要顺式作用序列，那么它们与蛋白质编码区及紧邻区域是不同的。文中讨论了一个模型，其中pl副突变导致染色质结构的可遗传变化，从根本上改变了植物发育过程中发生的调控相互作用。
