Knock-down of transcript abundance of a family of Kunitz proteinase inhibitor genes in white clover (Trifolium repens) reveals a redundancy and diversity of gene function

Development of two protocols for Agrobacterium-mediated transformation of white clover (Trifolium repens) via the callus system

White clover (Trifolium repens) is one of the most widely cultivated livestock forage plants whose persistence is severely affected by abiotic stresses. For the white clover, efficient regeneration systems is still a great necessity. In this study, inoculating 4-day-old cotyledons into MS media fortified with 0.4 mg·L-1 6-BA and 2 mg·L-1 2,4-D significantly increased the callus induction rate. Roots and cotyledons proved to be better explants, followed by hypocotyls, leaves, and petioles for callus induction. The development of differentiated structures occurred effectively on MS supplemented with 1 mg·L-1 6-BA and 0.1 mg·L-1 NAA. To increase transformation, we investigated various factors affecting the Agrobacterium tumefaciens transformation in white clover. The optimal conditions for root-derived callus and 4-day-old cotyledons were as follows: Agrobacterium suspension density with OD600 of 0.5, 20 mg·L-1 AS, and 4 days of co-cultivation duration. Subsequently, we developed two transformation protocols: transformation after callus induction from 4-day-old roots (Protocol A) and transformation before initiation of callus from cotyledons (Protocol B). The transformation frequencies varied from 1.92 to 3.17% in Protocol A and from 2.76 to 3.47% in Protocol B. We report the possibility to regenerate multiple transgenic white clover plants from a single genetic background. Our research may also contribute to successful genetic manipulation and genome editing in white clover.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03591-2.

Ubiquitin-independent, Proteasome-mediated targeted degradation of KRAS in pancreatic adenocarcinoma cells using an engineered ornithine decarboxylase/antizyme system

The oncogene KRAS not only promotes the tumorigenesis of pancreatic cancers but also is required for the malignant progression and metastasis of these cancers. Many methods have been explored to influence the malignant biological behavior of these cancers by targeting mutant KRAS. The ornithine decarboxylase/antizyme (ODC/AZ) system is another protein degradation pathway that exists in nature. The formation of an ODC and protein substrate complex through direct combination can promote its degradation by the 26S proteasome without ubiquitination, and this process can be catalyzed by AZ. In this study, we designed and reconstructed a chimeric fusion protein (named RC-ODC). The engineered fusion protein RC-ODC was confirmed to interact with the mutant KRAS oncoprotein in a co-immunoprecipitation assay, and the introduction of both RC-ODC and AZ resulted in degradation of the exogenous and endogenous mutant KRAS oncoprotein at the post-translational level independent of ubiquitination in vitro. Along with a decreased KRAS level, suppression of PANC-1 cell proliferation was detected in vitro and in vivo, and meanwhile downregulation of phosphorylated extracellular signal-regulated kinase 1/2 (ERK1/2) was also observed. Targeted degradation of the KRAS oncoprotein through the ODC/AZ pathway at the post-translational level may reflect a more effective future therapeutic strategy for pancreatic cancer patients. © 2018 The Authors. IUBMB Life published by Wiley Periodicals,Inc. on behalf of International Union of Biochemistry and Molecular Biology, 71(1):57-65, 2019.

An Alternative Nested Reading Frame May Participate in the Stress-Dependent Expression of a Plant Gene

Although plants as sessile organisms are affected by a variety of stressors in the field, the stress factors for the above-ground and underground parts of the plant and their gene expression profiles are not the same. Here, we investigated NbKPILP, a gene encoding a new member of the ubiquitous, pathogenesis-related Kunitz peptidase inhibitor (KPI)-like protein family, that we discovered in the genome of Nicotiana benthamiana and other representatives of the Solanaceae family. The NbKPILP gene encodes a protein that has all the structural elements characteristic of KPI but in contrast to the proven A. thaliana KPI (AtKPI), it does not inhibit serine peptidases. Unlike roots, NbKPILP mRNA and its corresponding protein were not detected in intact leaves, but abiotic and biotic stressors drastically affected NbKPILP mRNA accumulation. In search of the causes of suppressed NbKPILP mRNA accumulation in leaves, we found that the NbKPILP gene is "matryoshka," containing an alternative nested reading frame (ANRF) encoding a 53-amino acid (aa) polypeptide (53aa-ANRF) which has an amphipathic helix (AH). We confirmed ANRF expression experimentally. A vector containing a GFP-encoding sequence was inserted into the NbKPILP gene in frame with 53aa-ANRF, resulting in a 53aa-GFP fused protein that localized in the membrane fraction of cells. Using the 5'-RACE approach, we have shown that the expression of ANRF was not explained by the existence of a cryptic promoter within the NbKPILP gene but was controlled by the maternal NbKPILP mRNA. We found that insertion of mutations destroying the 53aa-ANRF AH resulted in more than a two-fold increase of the NbKPILP mRNA level. The NbKPILP gene represents the first example of ANRF functioning as a repressor of a maternal gene in an intact plant. We proposed a model where the stress influencing the translation initiation promotes the accumulation of NbKPILP and its mRNA in leaves.

Kunitz Proteinase Inhibitors Limit Water Stress Responses in White Clover (Trifolium repens L.) Plants

The response of plants to water deficiency or drought is a complex process, the perception of which is triggered at the molecular level before any visible morphological responses are detected. It was found that different groups of plant proteinase inhibitors (PIs) are induced and play an active role during abiotic stress conditions such as drought. Our previous work with the white clover (Trifolium repens L.) Kunitz Proteinase Inhibitor (Tr-KPI) gene family showed that Tr-KPIs are differentially regulated to ontogenetic and biotic stress associated cues and that, at least some members of this gene family may be required to maintain cellular homeostasis. Altered cellular homeostasis may also affect abiotic stress responses and therefore, we aimed to understand if distinct Tr-PKI members function during drought stress. First, the expression level of three Tr-KPI genes, Tr-KPI1, Tr-KPI2, and Tr-KPI5, was measured in two cultivars and one white clover ecotype with differing capacity to tolerate drought. The expression of Tr-KPI1 and Tr-KPI5 increased in response to water deficiency and this was exaggerated when the plants were treated with a previous period of water deficiency. In contrast, proline accumulation and increased expression of Tr-NCED1, a gene encoding a protein involved in ABA biosynthesis, was delayed in plants that experienced a previous drought period. RNAi knock-down of Tr-KPI1 and Tr-KPI5 resulted in increased proline accumulation in leaf tissue of plants grown under both well-watered and water-deficit conditions. In addition, increased expression of genes involved in ethylene biosynthesis was found. The data suggests that Tr-KPIs, particularly Tr-KPI5, have an explicit function during water limitation. The results also imply that the Tr-KPI family has different in planta proteinase targets and that the functions of this protein family are not solely restricted to one of storage proteins or in response to biotic stress.