Sathishraj Rajendran, Ju Yoonha, Gill Bikram S, Koo Dal-Hoe
Wheat Genetics Resource Center and Department of Plant Pathology, Kansas State University, Manhattan, KS, 66506, USA.
Chromosome Res. 2025 May 14;33(1):9. doi: 10.1007/s10577-025-09768-0.
Glyphosate resistance in crop weeds is commonly attributed to rapid evolution through the amplification of the target gene, EPSPS (5-enolpyruvylshikimate-3-phosphate synthase). This amplification typically occurs through mechanisms such as unequal recombination, segmental duplications within the target chromosome, or the formation of ring chromosomes and extrachromosomal circular (ecc) DNA elements containing EPSPS. However, structural abnormalities in chromosomes not directly associated with EPSPS amplification have not been documented in the glyphosate-resistant weed population. Here, we describe the presence of a large chromosome found exclusively in the glyphosate-resistant Amaranthus tuberculatus (waterhemp) population but absent in susceptible counterparts. This large chromosome (~ 6 μm) is approximately twice the size of normal chromosomes (~ 2-3 μm) and is present in both male and female euploid plants (2n = 32) in a heteromorphic state. It aroses through pericentromeric heterochromatin expansion and duplications of the 5S rDNA locus but notably lacks the EPSPS gene. The large chromosome pairs with its normal homolog but was not transmitted to progeny in controlled greenhouse matings, suggesting a fitness cost in the absence of glyphosate selection pressure. This large chromosome offers a potential resource for the investigation of chromosome evolution of adaptive traits for glyphosate resistance in A. tuberculatus.
作物杂草对草甘膦的抗性通常归因于通过靶基因5-烯醇丙酮酰莽草酸-3-磷酸合酶（EPSPS）的扩增而快速进化。这种扩增通常通过不等交换、靶染色体内部的片段重复、或形成包含EPSPS的环状染色体和染色体外环状（ecc）DNA元件等机制发生。然而，在抗草甘膦杂草群体中，尚未有与EPSPS扩增无直接关联的染色体结构异常的记录。在此，我们描述了一种仅在抗草甘膦的糙果苋（水麻）群体中发现、而在敏感群体中不存在的大染色体。这条大染色体（约6μm）的大小约为正常染色体（约2 - 3μm）的两倍，在雌雄整倍体植株（2n = 32）中均以异型状态存在。它是通过着丝粒周围异染色质扩展和5S rDNA位点的重复产生的，但明显缺乏EPSPS基因。这条大染色体与其正常同源染色体配对，但在可控温室杂交中未传递给后代，这表明在没有草甘膦选择压力的情况下存在适应性代价。这条大染色体为研究糙果苋对草甘膦抗性适应性状的染色体进化提供了一个潜在资源。
