Chen M, Jensen M, Rodermel S
Department of Botany, Iowa State University, Ames 50011, USA.
J Hered. 1999 Jan-Feb;90(1):207-14. doi: 10.1093/jhered/90.1.207.
The yellow variegated mutant of Arabidopsis thaliana is characterized by bright-yellow true leaves that turn green- and white-sectored as leaf development proceeds. Variegation is due to the action of a nuclear recessive gene. Whereas cells in the green sectors contain morphologically normal chloroplasts, cells in the yellow and white sectors are heteroplastidic and contain plastids with rudimentary lamellar structures, as well as some normal-appearing chloroplasts. This indicates that plastids in yellow variegated are affected differently by the nuclear mutation (the mutant is "plastid autonomous"). Genetic analyses have revealed that yellow variegated is an allele of the var2 locus, and that defective plastids are not maternally inherited. The traits of plastid autonomy and lack of maternal inheritance of the plastid defect set var2 apart from other nuclear gene-induced variegations and define a novel class of variegation mutant. The primary lesion in var2 probably does not involve a blockage in the pathways of pigment biosynthesis. Under high temperatures or low light conditions, plant growth is retarded and mutant plants are nearly all-green. Considered together, our data suggest that var2 is delayed in chloroplast biogenesis. We suggest that the stochastic pattern of variegation in the mutant may be due to an interplay of factors that regulate var2 gene expression and factors that mediate rates of cell and plastid division. Plastids with a critical threshold of the partially functional var2 protein are green, while plastids containing less than the threshold of var2 activity are white.
拟南芥黄色杂色突变体的特征是真叶呈亮黄色，随着叶片发育，会变成绿色和白色相间的样子。杂色是由一个核隐性基因的作用引起的。绿色区域的细胞含有形态正常的叶绿体，而黄色和白色区域的细胞是异质体，含有具有原始层状结构的质体以及一些外观正常的叶绿体。这表明黄色杂色突变体中的质体受核突变的影响不同（该突变体是“质体自主的”）。遗传分析表明，黄色杂色突变体是var2位点的一个等位基因，有缺陷的质体不是母系遗传的。质体自主性以及质体缺陷不具有母系遗传的特性，使var2与其他核基因诱导的杂色不同，并定义了一类新的杂色突变体。var2的主要损伤可能不涉及色素生物合成途径的阻断。在高温或弱光条件下，植物生长受阻，突变体植株几乎全为绿色。综合来看，我们的数据表明var2在叶绿体生物发生过程中延迟。我们认为，突变体中杂色的随机模式可能是由于调节var2基因表达的因素与介导细胞和质体分裂速率的因素相互作用所致。具有部分功能性var2蛋白临界阈值的质体是绿色的，而var2活性低于阈值的质体是白色的。
