Composite plants for a composite plant: An efficient protocol for root studies in the sunflower using composite plants approach

Sunflower ( Helianthus annuus L .) is important oilseed crop in the world and the sunflower oil is prized for its’ exceptional quality and flavor. The recent availability of the sunflower genome can allow genome-wide characterization of genes and gene families. With plant transformation usually being the rate limiting step for gene functional studies of sunflower, composite plants can alleviate this bottleneck. Composite plants, produced using Agrobacterium rhizogenes , are plants with transgenic roots and wild type shoots. Composite plants offer benefits over creating fully transgenic plants, namely time and cost. Here we outlined the critical steps and parameters for a protocol for the sunflower composite plants production. We use more than a dozen genotypes and three constitutive promoters to validates the utility and efficiency of this protocol. Moreover, functional gene characterization by overexpression and RNAi silencing of a root related transcription factor HaLBD16 further emphasize the value of the system in the sunflower studies. With the protocol developed here an experiment can be carried out with efficiency and in only two months. This procedure adds to arsenal of approaches for the functional genetics/genomics in sunflower for characterization candidate genes involved in root development and stress adaptation. Key message Composite plants technique described here is fast and efficient approach for roots functional studies in sunflower.