An efficient method for stable protein targeting in grasses (Poaceae): a case study in Puccinellia tenuiflora

Application of In Vitro Plant Tissue Culture Techniques to Halophyte Species: A Review

Halophytes are plants able to thrive in environments characterized by severe abiotic conditions, including high salinity and high light intensity, drought/flooding, and temperature fluctuations. Several species have ethnomedicinal uses, and some are currently explored as sources of food and cosmetic ingredients. Halophytes are considered important alternative cash crops to be used in sustainable saline production systems, due to their ability to grow in saline conditions where conventional glycophyte crops cannot, such as salt-affected soils and saline irrigation water. In vitro plant tissue culture (PTC) techniques have greatly contributed to industry and agriculture in the last century by exploiting the economic potential of several commercial crop plants. The application of PTC to selected halophyte species can thus contribute for developing innovative production systems and obtaining halophyte-based bioactive products. This work aimed to put together and review for the first time the most relevant information on the application of PTC to halophytes. Several protocols were established for the micropropagation of different species. Various explant types have been used as starting materials (e.g., basal shoots and nodes, cotyledons, epicotyls, inflorescence, internodal segments, leaves, roots, rhizomes, stems, shoot tips, or zygotic embryos), involving different micropropagation techniques (e.g., node culture, direct or indirect shoot neoformation, caulogenesis, somatic embryogenesis, rooting, acclimatization, germplasm conservation and cryopreservation, and callogenesis and cell suspension cultures). In vitro systems were also used to study physiological, biochemical, and molecular processes in halophytes, such as functional and salt-tolerance studies. Thus, the application of PTC to halophytes may be used to improve their controlled multiplication and the selection of desired traits for the in vitro production of plants enriched in nutritional and functional components, as well as for the study of their resistance to salt stress.

Establishment of an efficient Agrobacterium-mediated genetic transformation system in halophyte Puccinellia tenuiflora

Alkaligrass (Puccinellia tenuiflora) is a monocotyledonous halophyte pasture, which has strong tolerance to saline-alkali, drought, and chilling stresses. We have reported a high-quality chromosome-level genome and stress-responsive proteomic results in P. tenuiflora. However, the gene/protein function investigations are still lacking, due to the absent of genetic transformation system in P. tenuiflora. In this study, we established a higher efficient Agrobacterium-mediated transformation for P. tenuiflora using calluses induced from seeds. Agrobacterium strain EHA105 harbors pANIC 6B vectors that contain GUS reporter gene and Hyg gene for screening. Ten mg·L-1 hygromycin was used for selecting transgenic calluses. The optimized condition of vacuum for 10 min, ultrasonication for 10 min, and then vacuum for 10 min was used for improvement of conversion efficiency. Besides, 300 mg·L-1 timentin was the optimum antibiotics in transformation. PCR amplification exhibited that GUS gene has been successfully integrated into the chromosome of P. tenuiflora. Histochemical GUS staining and qRT-PCR analysis indicated that GUS gene has stably expressed with ß-glucuronidase activity in transgene seedlings. All these demonstrated that we have successfully established an Agrobacterium-mediated transformation system of P. tenuiflora, which provides a good platform for further gene function analysis and lays a solid foundation for molecular breeding.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-021-01247-8.

Subcellular Localization of Rice Acyl-CoA-Binding Proteins ACBP4 and ACBP5 Supports Their Non-redundant Roles in Lipid Metabolism

Acyl-CoA-binding proteins (ACBPs), conserved at the acyl-CoA-binding domain, can bind acyl-CoA esters as well as transport them intracellularly. Six ACBPs co-exist in each model plant, dicot Arabidopsis thaliana (thale cress) and monocot Oryza sativa (rice). Although Arabidopsis ACBPs have been studied extensively, less is known about the rice ACBPs. OsACBP4 is highly induced by salt treatment, but down-regulated following pathogen infection, while OsACBP5 is up-regulated by both wounding and pathogen treatment. Their differential expression patterns under various stress treatments suggest that they may possess non-redundant functions. When expressed from the CaMV35S promoter, OsACBP4 and OsACBP5 were subcellularly localized to different endoplasmic reticulum (ER) domains in transgenic Arabidopsis. As these plants were not stress-treated, it remains to be determined if OsACBP subcellular localization would change following treatment. Given that the subcellular localization of proteins may not be reliable if not expressed in the native plant, this study addresses OsACBP4:GFP and OsACBP5:DsRED expression from their native promoters to verify their subcellular localization in transgenic rice. The results indicated that OsACBP4:GFP was targeted to the plasma membrane besides the ER, while OsACBP5:DsRED was localized at the apoplast, in contrast to their only localization at the ER in transgenic Arabidopsis. Differences in tagged-protein localization in transgenic Arabidopsis and rice imply that protein subcellular localization studies are best investigated in the native plant. Likely, initial targeting to the ER in a non-native plant could not be followed up properly to the final destination(s) unless it occurred in the native plant. Also, monocot (rice) protein targeting may not be optimally processed in a transgenic dicot (Arabidopsis), perhaps arising from the different processing systems for routing between them. Furthermore, changes in the subcellular localization of OsACBP4:GFP and OsACBP5:DsRED were not detectable following salt and pathogen treatment, respectively. These results suggest that OsACBP4 is likely involved in the intracellular shuttling of acyl-CoA esters and/or other lipids between the plasma membrane and the ER, while OsACBP5 appears to participate in the extracellular transport of acyl-CoA esters and/or other lipids, suggesting that they are non-redundant proteins in lipid trafficking.

A Protoplast Transient Expression System to Enable Molecular, Cellular, and Functional Studies in Phalaenopsis orchids

The enigmatic nature of the specialized developmental programs of orchids has fascinated plant biologists for centuries. The recent releases of orchid genomes indicate that orchids possess new gene families and family expansions and contractions to regulate a diverse suite of developmental processes. However, the extremely long orchid life cycle and lack of molecular toolkit have hampered the advancement of orchid biology research. To overcome the technical difficulties and establish a platform for rapid gene regulation studies, in this study, we developed an efficient protoplast isolation and transient expression system for Phalaenopsis aphrodite. This protocol was successfully applied to protein subcellular localization and protein-protein interaction studies. Moreover, it was confirmed to be useful in delineating the PaE2F/PaDP-dependent cell cycle pathway and studying auxin response. In summary, the established orchid protoplast transient expression system provides a means to functionally characterize orchid genes at the molecular level allowing assessment of transcriptome responses to transgene expression and widening the scope of molecular studies in orchids.