Data from: Transgenes in Mexican maize: molecular evidence and methodological considerations for GMO detection in landrace populations

A possible consequence of planting GMOs in centers of crop origin is unintended gene flow into traditional landraces. In 2001, a study reported the presence of the transgenic 35S promoter in maize landraces sampled in 2000 from the Sierra Juarez of Oaxaca, Mexico. Analysis of a large sample taken from the same region in 2003 and 2004 could not confirm the existence of transgenes, thereby casting doubt on the earlier results. These two studies were based on different sampling and analytical procedures and are thus hard to compare. Here we present new molecular data for this region that confirm the presence of transgenes in three of 23 localities sampled in 2001. Transgene sequences were not detected in samples taken in 2002 from nine localities, while directed samples taken in 2004 from two of the positive 2001 localities were again found to contain transgenic sequences. These findings suggest the persistence or re-introduction of transgenes up until 2004 in this area. We address variability in recombinant sequence detection by analyzing the consistency of current molecular assays. We also present theoretical results on the limitations of estimating the probability of transgene detection in samples taken from landraces. The inclusion of a limited number of female gametes, but more importantly, aggregated transgene distributions may significantly lower detection probabilities. Our analytical and sampling considerations help explain discrepancies among different detection efforts, including the one presented here, and provide considerations for the establishment of monitoring protocols to detect the presence of transgenes among structured populations of landraces.

在作物起源中心种植转基因生物（Genetically Modified Organisms, GMOs）可能引发的潜在风险之一，是外源基因向传统地方品种发生非预期漂移。2001年，一项研究报道称，2000年从墨西哥瓦哈卡州胡阿雷斯山区采集的玉米地方品种样本中，检出转基因35S启动子。2003年与2004年针对该区域开展的大样本分析未能证实转基因的存在，因此对早期研究结果提出了质疑。两项研究采用了不同的采样与分析流程，故难以直接对比。
本研究针对该区域提供了全新的分子数据，证实2001年采样的23个地点中，有3个存在转基因序列。2002年从9个地点采集的样本未检测到转基因序列；而2004年针对2001年检测呈阳性的2个地点开展的定向采样样本中，再次检出转基因序列。上述结果表明，直至2004年，该区域仍存在转基因的持续存留或重新引入现象。
我们通过分析当前分子检测实验的一致性，探讨了重组序列检测结果的变异性问题。同时，针对从地方品种样本中估算转基因检出概率的局限性，本研究给出了理论分析结果。研究发现，仅采集少量雌性配子，更关键的是转基因的聚集分布特征，会显著降低检出概率。我们的分析与采样考量，有助于解释不同检测工作（包括本研究的检测工作）间的结果差异，并为建立针对结构化地方品种种群的转基因监测方案提供参考依据。