A simple and robust Agrobacterium-mediated gene expression system in the C4 panicoid model crop, foxtail millet has been developed with up to 27 % transformation efficiency. Foxtail millet (Setaria italica L.) is a model crop to study C4 photosynthesis, abiotic stress tolerance, and bioenergy traits. Advances in molecular genetics and genomics had identified several potential genes in this crop that would serve as candidates for imparting climate-resilient traits in related millets, cereals, and biofuel crops. However, the lack of an efficient genetic transformation system has been impeding the functional characterization of these genes in foxtail millet per se. Given this, an easy and efficient regeneration and transformation protocol was optimized using mature seeds as a choicest explant. The suitability of secondary embryogenic calli over primary calli is underlined due to their high competence. The use of perfect combinations of plant growth regulators together with the ionic strength of organic and inorganics salts was found to influence regeneration and genetic transformation. We studied and optimized various crucial factors that affect the genetic transformation of foxtail millet calli using Agrobacterium tumefaciens-mediated approach. Secondary embryogenic calli and LBA44404 strain were found to be the best targets for transformation. The use of high sucrose and glucose, together with freshly prepared tobacco leaves extract, Silwet L-77 and acetosyringone, improved the efficiency of the genetic transformation of foxtail millet. Moreover, the use of an in vitro regeneration system with 84% callusing efficiency and 70-74% regeneration frequency led to a high recovery of transformants. Altogether, the present study reports a highly efficient (~ 27%) transformation system in foxtail millet that will expedite forward and reverse genetic studies in this important crop.

中文翻译：

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一种有效的农杆菌介导的谷子 (Setaria italica L.) 遗传转化方法。

在 C4 穗状花序模式作物谷子中开发了一种简单而强大的农杆菌介导的基因表达系统，转化效率高达 27%。谷子 (Setaria italica L.) 是研究 C4 光合作用、非生物胁迫耐受性和生物能源性状的模式作物。分子遗传学和基因组学的进展已经确定了这种作物中的几个潜在基因，这些基因将作为赋予相关小米、谷物和生物燃料作物适应气候的特性的候选基因。然而，缺乏有效的遗传转化系统一直阻碍这些基因在谷子本身中的功能表征。鉴于此，使用成熟种子作为最佳外植体优化了简单有效的再生和转化方案。次生胚性愈伤组织对初级愈伤组织的适用性因其高能力而被强调。发现植物生长调节剂与有机盐和无机盐的离子强度的完美组合会影响再生和遗传转化。我们使用农杆菌介导的方法研究和优化了影响谷子愈伤组织遗传转化的各种关键因素。发现次生胚性愈伤组织和 LBA44404 菌株是转化的最佳目标。使用高蔗糖和葡萄糖，以及新鲜制备的烟叶提取物、Silwet L-77和乙酰丁香酮，提高了谷子遗传转化的效率。而且，使用具有 84% 愈伤组织效率和 70-74% 再生频率的体外再生系统导致转化体的高回收率。总之，本研究报告了一种高效（~27%）的谷子转化系统，将加快这一重要作物的正向和反向遗传研究。