Santos-Serejo Janay A, Gardingo José R, Mondin Mateus, Aguiar-Perecin Margarida L R
Department of Genetics, Luiz de Queiroz College of Agriculture, University of São Paulo, Piracicaba, Brazil.
Cytogenet Genome Res. 2018;154(2):107-118. doi: 10.1159/000488067. Epub 2018 Apr 11.
The meiotic and mitotic behavior of regenerated plants derived from a long-term callus culture, designated 12-F, was analyzed. This culture was heterozygous for an amplification of the heterochromatic knob on the long arm of chromosome 7 (K7L). We aimed to investigate if the amplification resulted from a breakage-fusion-bridge (BFB) cycle or from unequal sister chromatid recombination. Therefore, C-banded mitotic metaphases and pachytene, diakinesis, and anaphase I of regenerated plants were analyzed. Additionally, the occurrence of alterations in K7L was investigated in C-banded metaphases from short-term callus cultures derived from lines related to the donor genotype of the 12-F culture. As a result, plants homozygous and heterozygous for the amplification were detected. Meiosis was normal with few abnormalities, such as a low frequency of univalents at diakinesis. In the callus cultures a chromosome 7 with knobs of different sizes in the sister chromatids was detected and interpreted as a result of unequal crossing over. Other chromosomal alterations were consistent with the occurrence of BFB cycles. The finding of unequal crossing over in the cultures supports the conclusion that the amplification in the culture 12-F would be derived from this mechanism. If the amplification was derived from a BFB cycle, the terminal euchromatic segment between knob and the telomere would be deleted, and possibly, homozygous plants would not be viable.
对源自长期愈伤组织培养物（命名为12-F）的再生植株的减数分裂和有丝分裂行为进行了分析。该培养物对于7号染色体长臂上异染色质结（K7L）的扩增是杂合的。我们旨在研究这种扩增是由断裂-融合-桥（BFB）循环还是由不等姐妹染色单体重组导致的。因此，对再生植株的C带染色有丝分裂中期以及粗线期、终变期和减数第一次分裂后期进行了分析。此外，在源自与12-F培养物供体基因型相关品系的短期愈伤组织培养物的C带染色中期，研究了K7L的改变情况。结果，检测到了扩增的纯合和杂合植株。减数分裂正常，仅有少数异常情况，例如终变期单价体频率较低。在愈伤组织培养物中，检测到一条7号染色体，其姐妹染色单体上有大小不同的结，这被解释为不等交换的结果。其他染色体改变与BFB循环的发生一致。在培养物中发现不等交换支持了这样的结论，即12-F培养物中的扩增是由这种机制产生的。如果扩增是由BFB循环导致的，那么结与端粒之间的末端常染色质区段将会缺失，并且纯合植株可能无法存活。
