pCYOs: Binary vectors for simple visible selection of transformants using an albino-cotyledon mutant in Arabidopsis thaliana

Several selection markers for the screening of transformants have been developed; however, simple and reliable methods are generally preferred. We have developed a novel visible selection system for the identification of transformants in Arabidopsis thaliana that does not require any special reagent and/or equipment except using the albino-cotyledon mutant cyo1. In this system, the pCYO vector carrying the CYO1 genomic fragment as a selection marker is introduced into the cyo1 mutant. Transformation is performed by the Agrobacterium-mediated floral dip method and resultant T₁ seeds are sown in soil. Seedlings with green cotyledons, not albino, are expected to be 'complemented' transformants with the transgene of interest. This system provides a very simple selection method that can be performed without any special equipment, reagent, sterile conditions, or UV illumination. We have constructed three vectors, (1) pCYO1, an empty vector; (2) pCYO2, an overexpression vector carrying CaMV35S promoter; and (3) pCYO3, a vector for genome editing, carrying the CRISPR/Cas9 cassette. Example transformation experiments using these vectors, including genome editing, are shown.

Rice CYO1, an ortholog of Arabidopsis thaliana cotyledon chloroplast biogenesis factor AtCYO1, is expressed in leaves and involved in photosynthetic performance

In the dicotyledonous plant Arabidopsis thaliana, the cotyledon chloroplast biogenesis factor AtCYO1 is crucial for the biogenesis of cotyledon chloroplasts. Arabidopsis mutants lacking AtCYO1 have pale cotyledons but develop normal mature leaves. In the monocotyledonous plant Oryza sativa, the gene OsCYO1 has high sequence identity to AtCYO1, but its function is unknown. We examined the role of OsCYO1 in O. sativa. We first confirmed that transformation with OsCYO1 could recover the phenotype of the Arabidopsis cyo1 mutant. Similar to AtCYO1, recombinant OsCYO1 has protein disulfide reductase (PDR) activity, which increased as a function of dieosin glutathione disulfide concentration with an apparent K_m of 3.2μM and K_cat of 0.53min^-1. The PDR activity was reduced when NADPH or NADH was used as an electron donor; however, PDR activity was observed with OsCYO1 and glutathione, suggesting that glutathione may serve as a reducing agent for OsCYO1 in vivo. In O. sativa, the OsCYO1 transcript level was higher in leaves compared with the coleoptile, which is the first leaf-like organ that forms during rice embryogenesis. Many OsCYO1 mutant lines defective in RNA interference had green leaves, however, three mutant lines had not only albino coleoptile but also albino leaves. Those having green leaves reduced photosynthetic performance in leaves. Our results demonstrate that OsCYO1 is enzymatically equivalent to AtCYO1 but that the physiological role of OsCYO1 in monocotyledonous plants may differ from that of AtCYO1 in dicotyledonous plants.