SbRFP1 regulates cold-induced sweetening of potato tubers by inactivation of StBAM1.

Potato cold-induced sweetening (CIS) is a major drawback restricting potato process industry. Starch degradation and sucrose decomposition are considered to be the key pathways in potato CIS. Our previous study showed that the RING finger gene SbRFP1 could slow down starch degradation and the accumulation of reducing sugars (RS) through inhibiting amylase and invertase activity in cold-stored tubers. However, the regulation mechanism of SbRFP1 is not clear. In this paper, we first proved that SbRFP1 could promote starch synthesis and modify the shape of starch granules. By further yeast two hybrid, GST-pull down and inhibition of enzyme activity assays, we confirmed that SbRFP1 could slow down the transformation of starch to RS in tubers mainly through the inhibition of ß-amylase StBAM1 activity. SbRFP1 was also proved to possess E3 ubiquitin ligase activity by ubiquitination assay. Thus, SbRFP1 may regulate the accumulation of RS in cold-stored tubers by ubiquitination and degradation of StBAM1. Therefore, our study reveals the regulatory mechanism of SbRFP1 in the process of CIS and provides more powerful evidence for the effect of starch degradation on potato CIS.

A novel RING finger gene, SbRFP1, increases resistance to cold-induced sweetening of potato tubers.

The modulation of the activity of enzymes associated with carbohydrate metabolism is important for potato cold-induced sweetening (CIS). A novel RING finger gene SbRFP1 was cloned and its expression was found to be cold-inducible in potato tubers of the CIS-resistant genotypes. Transformation of SbRFP1 in potatoes confirmed its role in inhibiting ß-amylase and invertase activity, which consequently slowed down starch and sucrose degradation and the accumulation of reducing sugars in cold stored tubers. These findings strongly suggest that SbRFP1 may function as a negative regulator of BAM1 and StvacINV1 to decelerate the accumulation of reducing sugars in the process of potato CIS.

Type I interferon-dependent and -independent expression of tripartite motif proteins in immune cells.

The tripartite motif (TRIM) proteins are important in a variety of cellular functions additional to anti-viral activity. We systematically analysed mRNA expression of representative TRIM molecules in mouse macrophages, myeloid and plasmacytoid dendritic cells, and a selection of CD4(+) T cell subsets. We defined four clusters of TRIM genes based on their selective expression in these cells. The first group of TRIM genes was preferentially expressed in CD4(+) T cells and contained the COS-FN3 motif previously shown to be involved in protein interactions. Additional TRIM genes were identified that showed up-regulation in macrophages and dendritic cells upon influenza virus infection in a type I IFN-dependent manner, suggesting that they have anti-viral activity. In support of this notion, a subset of these TRIM molecules mapped to mouse chromosome 7, syntenic to human chromosome 11, where TRIM family members such as TRIM5, shown to have anti-viral activity, are localized. A distinct group of TRIM was constitutively expressed in plasmacytoid dendritic cells independently of viral infection or signalling through the type I IFN receptor. Our findings on expression and regulation of TRIM genes in cells of the immune system that have different effector functions in innate and adaptive immune responses, may provide leads for determining functions of this diverse family of molecules.

Sequence, expression and tissue localization of a gene encoding a makorin RING zinc-finger protein in germinating rice (Oryza sativa L. ssp. Japonica) seeds.

The makorin (MKRN) RING finger protein gene family encodes proteins (makorins) with a characteristic array of zinc-finger motifs and which are present in a wide array of eukaryotes. In the present study, we analyzed the structure and expression of a putative makorin RING finger protein gene in rice (Oryza sativa L. ssp. Japonica cv. Nipponbare). From the analysis of the genomic (AP003543), mRNA (AK120250) and deduced protein (BAD61603) sequences of the putative MKRN gene of rice, obtained from GenBank, we found that it was indeed a bona fide member of the MKRN gene family. The rice MKRN cDNA encoded a protein with four C3H zinc-finger-motifs, one putative Cys-His zinc-finger motif, and one RING zinc-finger motif. The presence of this distinct motif organization and overall amino acid identity clearly indicate that this gene is indeed a true MKRN ortholog. We isolated RNA from embryonic axes of rice seeds at various stages of imbibition and germination and studied the temporal expression profile of MKRN by RT-PCR. This analysis revealed that MKRN transcripts were present at all the time points studied. It was at very low levels in dry seeds, increased slowly during imbibition and germination, and slightly declined in the seedling growth stage. After 6days of germination, an organ-dependent expression pattern of MKRN was observed: highest in roots and moderate in leaves. Similarly to MKRN transcripts, transcripts of cytoskeletal actin and tubulin were also detected in dry embryos, steadily increased during imbibition and germination and leveled off after 24h of germination. We studied the spatial expression profile of MKRN in rice tissues, by using a relatively fast, simple and effective non-radioactive mRNA in situ hybridization (NRISH) technique, which provided the first spatial experimental data that hints at the function of a plant makorin. This analysis revealed that MKRN transcripts were expressed in young plumules, lateral root primordia, leaf primordia, leaves and root tissues at many different stages of germination. The presence of MKRN transcripts in dry seeds, its early induction during germination and its continued spatiotemporal expression during early vegetative growth suggest that MKRN has an important role in germination, leaf and lateral root morphogenesis and overall development in rice.