Consonni G, Ronchi A, Pilu R, Gavazzi G, Dellaporta S L, Tonelli C
Dipartimento di Genetica e di Biologia dei Microrganismi, Università degli Studi di Milano, Italy.
Mol Gen Genet. 1997 Oct;256(3):265-76. doi: 10.1007/s004380050569.
The duplicated R and Sn genes are involved in the regulation of the maize anthocyanin biosynthetic pathway, encoding tissue-specific products that are homologous to the helix-loop-helix transcriptional activators. Sn determines the pigmentation of the mesocotyl, leaf basis and pericarp, while R determines pigmentation in various tissues, but not in the mesocotyl. In the progeny derived from test-crosses of R/Sn heterozygous plants, a high frequency of R plants exhibiting mesocotyl pigmentation was observed; these derivatives were defined as R*. In R* plants, the presence of this novel trait was not accompanied by the acquisition of Sn or by gross DNA rearrangements in the R profile. Accordingly, RT-PCR analysis showed that mesocotyl pigmentation in R* was attributable to the resident R gene. The occurrence of R* was observed with all R alleles tested, and was enhanced when a P component was present. The heritability of R* was shown only in the case of the standard R-r allele, which carries a functional P component. In addition, we observed that R* can influence other R alleles, transferring the ability to pigment the mesocotyl. R* is unstable, showing a tendency to return to its original state after a few generations. In R* plants there was a correlation between observed ectopic pigmentation and an increase in the level of A1 transcript but, surprisingly, not in the accumulation of R transcript. The results obtained from the analysis of test crosses of rSn/r delta plants suggest that an unlinked genetic factor accounts for the ectopic pigmentation. Concomitant occurrence of epigenetic events might explain the observed instability and reversibility noted above. Further study of this phenomenon might help to elucidate the basis of the interaction between homologous and non-homologous regulators.
重复的R和Sn基因参与玉米花青素生物合成途径的调控，编码与螺旋-环-螺旋转录激活因子同源的组织特异性产物。Sn决定中胚轴、叶基部和果皮的色素沉着，而R决定各种组织中的色素沉着，但不包括中胚轴。在R/Sn杂合植物测交产生的后代中，观察到高频率的表现出中胚轴色素沉着的R植株；这些衍生物被定义为R*。在R植株中，这种新性状的出现并未伴随着Sn的获得或R基因图谱中的大规模DNA重排。因此，RT-PCR分析表明，R植株的中胚轴色素沉着归因于常驻的R基因。在所有测试的R等位基因中都观察到了R的出现，并且当存在P元件时其出现频率增加。仅在携带功能性P元件的标准R-r等位基因的情况下显示出R的遗传性。此外，我们观察到R可以影响其他R等位基因，赋予中胚轴色素沉着的能力。R是不稳定的，在几代之后有恢复到其原始状态的趋势。在R*植株中，观察到的异位色素沉着与A1转录本水平的增加之间存在相关性，但令人惊讶的是，与R转录本的积累无关。对rSn/r delta植株测交分析的结果表明，一个不连锁的遗传因子导致了异位色素沉着。表观遗传事件的同时发生可能解释了上述观察到的不稳定性和可逆性。对这一现象的进一步研究可能有助于阐明同源和非同源调节因子之间相互作用的基础。
