An E3 ubiquitin ligase CSIT2 controls critical sterility-inducing temperature of thermo-sensitive genic male sterile rice.

Thermo-sensitive genic male sterile (TGMS) lines are the core of two-line hybrid rice (Oryza sativa). However, elevated or unstable critical sterility-inducing temperatures (CSITs) of TGMS lines are bottlenecks that restrict the development of two-line hybrid rice. However, the genes and molecular mechanisms controlling CSIT remain unknown. Here, we report the CRITICAL STERILITY-INDUCING TEMPERATURE 2 (CSIT2) that encodes a really interesting new gene (RING) type E3 ligase, controlling the CSIT of thermo-sensitive male sterility 5 (tms5)-based TGMS lines through ribosome-associated protein quality control (RQC). CSIT2 binds to the large and small ribosomal subunits and ubiquitinates 80S ribosomes for dissociation, and may also ubiquitinate misfolded proteins for degradation. Mutation of CSIT2 inhibits the possible damage to ubiquitin system and protein translation, which allows more proteins such as catalases to accumulate for anther development and inhibits abnormal accumulation of reactive oxygen species (ROS) and premature programmed cell death (PCD) in anthers, partly rescuing male sterility and raised the CSIT of tms5-based TGMS lines. These findings reveal a mechanism controlling CSIT and provide a strategy for solving the elevated or unstable CSITs of tms5-based TGMS lines in two-line hybrid rice.

In planta high levels of hydrolysable tannins inhibit peroxidase mediated anthocyanin degradation and maintain abaxially red leaves of Excoecaria Cochinchinensis.

BACKGROUND: Abaxially anthocyanic leaves of deeply-shaded understorey plants play important ecological significance for the environmental adaption. In contrast to the transient pigmentation in other plants, anthocyanins are permanently presented in these abaxially red leaves, however, the mechanism for the pigment maintenance remains unclear. In the present study, we investigated phenolic metabolites that may affect pigment stability and degradation in Excoecaria cochinchinensis (a bush of permanently abaxial-red leaves), via a comparison with Osmanthus fragrans (a bush of transiently red leaves). RESULTS: High levels of galloylated anthocyanins were identified in the Excoecaria but not in the Osmanthus plants. The galloylated anthocyanin showed slightly higher stability than two non-galloylated anthocyanins, while all the 3 pigments were rapidly degraded by peroxidase (POD) in vitro. High levels of hydrolysable tannins [mainly galloylglucoses/ellagitannins (GGs/ETs)] were identified in Excoecaria but none in Osmanthus. GGs/ETs showed inhibition effect on POD, with IC50 ranged from 35.55 to 83.27 µM, correlated to the markedly lower POD activities detected in Excoecaria than in Osmanthus. Strong copigmentation was observed for GGs/ETs and anthocyanins, with more than 30% increase in the red intensity of non-galloylated anthocyanin solutions. In the leaf tissue, the hydrolysable tannins were observed to be co-localized with anthocyanins at the abaxial layer of the Excoecaria leaves, correlated to the low POD activity, more acidity and increased red intensity of the tissue. CONCLUSION: The results suggest that the Excoecaria leaves accumulate a distinct group of phenolic metabolites, mainly GGs/ETs, at the abaxial layer, which prevent anthocyanin degradation and increase the pigment stability, and consequently lead to the permanent maintenance of the red leaves.

Characterization of Active Anthocyanin Degradation in the Petals of Rosa chinensis and Brunfelsia calycina Reveals the Effect of Gallated Catechins on Pigment Maintenance.

Anthocyanin degradation decreases ornamental or nutritional values of horticultural products. To investigate factors that may influence colour change in flower development, anthocyanin degradation was compared between the flowers of Brunfelsia calycina and Rosa chinensis, which show rapid and slow degradation, respectively. In-gel activity assays, high performance liquid chromatography (HPLC) analysis of tannins, enzyme kinetics measurement and immune-detection of anthocyanin degradation related-perioxidases (PODs) were carried out for the comparison. Rose petals possessed significantly lower anthocyanin degradation-related POD activities than Brunfelsia petals, which may be related to the high tannin contents. Epicatechin gallate (ECG) and gallocatechin gallate (GCG) were detected in rose as 161.3 ± 12.34 and 273.56 ± 41.23 µg/g FW (Fresh Weight) respectively, while not detected in Brunfelsia. ECG and GCG inhibited the activities of the Brunfelsia POD with half maximal inhibitory concentrations (IC50s) as 21.5 and 29.7 µM respectively, and increased the colour intensities of the anthocyanins. Catechin and epicatechin did not inhibit the POD activity, while serving as POD substrates, with Km (the Michaelis constant) as 0.48 and 1.23 mM. Similar protein levels of the anthocyanin degradation-related 40-kDa PODs were detected in Brunfelsia and rose. In summary, high amount of tannins, particularly ECG and GCG, in red rose petals may inhibit the degradation-related enzymes, leading to the maintenance of anthocyanins in vivo.