In this protocol, we describe the growth and establishment of stable transgenic lines for the extremophyte model Schrenkiella parvula. The availability of an efficient transformation system is a hallmark of any versatile genetic model. Plants that thrive in extreme environments, referred to as extremophytes, provide a critical resource for understanding plant adaptations to environmental stresses. Schrenkiella parvula (formerly Thellungiella parvula and Eutrema parvulum) is one such extremophyte model, with expanding genomic resources1,2,3,4,5. However, transformation protocols have not yet been reported for S. parvula in published studies.
The genome of S. parvula is the first published extremophyte genome in Brassicaceae (mustard-cabbage family) and shows an extensive overall genome synteny with the non-extremophyte model, Arabidopsis thaliana1. Thus, comparative studies between A. thaliana and S. parvula could benefit from the wealth of genetic studies performed on A. thaliana to make informative hypotheses on how the S. parvula genome has evolved and regulated differently to cope with extreme environmental stresses5,6,7. S. parvula is one of the most salt-tolerant species (based on soil NaCl LD50) among known wild relatives of A. thaliana8. In addition to the NaCl tolerance, S. parvula survives and completes its life cycle in the presence of multiple salt ions at high concentrations toxic to most plants7. In response to the abiotic stresses prevalent in its natural habitat, it has evolved various traits, among which several have been studied at the biochemical or physiological level 8,9,10,11.
Since 2010, there have been over 400 peer-reveiwed publications that used S. parvula as a target species or used it in a comparison with other plant genomes. However, a clear bottleneck could be identified with a closer look of what type of studies have been conducted. The majority of these reports discuss the potential use of S. parvula in future studies or use it in comparative genomic or phylogenomic studies. Due to the lack of a proof-of-concept transformation protocol established for S. parvula, it has not been used in functional genomic studies, despite having one of the highest quality plant genomes available to date (>5 Mb contig N50) assembled and annotated into chromosome-level pseudomolecules1.
The Agrobacterium-mediated floral-dip transformation method has become the most broadly used method to create trasngenic lines in A. thaliana, and the development of a reproducible system of transformation was a critical factor in its success as a genetic model12,13. However, not all Brassicaceae species have been shown to be successfully transformed using the floral-dip method developed for A. thaliana. Specially, the Brassicaceae Lineage II species that include S. parvula has been recalcitrant to floral-dip based transformation methods14,15.
The indeterminate flowering growth habit of S. parvula, combined with its narrow leaf morphology has made it challenging to adopt the standard Agrobacterium-mediated floral-dip transformation method. In this study, we report the modified protocol we have developed for reproducible transformation of S. parvula.