SUMOylation regulates Lem2 function in centromere clustering and silencing.

Regulation by the small modifier SUMO is heavily dependent on spatial control of enzymes that mediate the attachment and removal of SUMO on substrate proteins. Here, we show that in the fission yeast Schizosaccharomyces pombe, delocalisation of the SUMO protease Ulp1 from the nuclear envelope results in centromeric defects that can be attributed to hyper-SUMOylation at the nuclear periphery. Unexpectedly, we find that although this localised hyper-SUMOylation impairs centromeric silencing, it can also enhance centromere clustering. Moreover, both effects are at least partially dependent on SUMOylation of the inner nuclear membrane protein Lem2. Lem2 has previously been implicated in diverse biological processes, including the promotion of both centromere clustering and silencing, but how these distinct activities are coordinated was unclear; our observations suggest a model whereby SUMOylation serves as a regulatory switch, modulating Lem2 interactions with competing partner proteins to balance its roles in alternative pathways. Our findings also reveal a previously unappreciated role for SUMOylation in promoting centromere clustering.

Initiation of scutellum-derived callus is regulated by an embryo-like developmental pathway in rice.

In rice (Oryza sativa) tissue culture, callus can be induced from the scutellum in embryo or from the vasculature of non-embryonic organs such as leaves, nodes, or roots. Here we show that the auxin signaling pathway triggers cell division in the epidermis of the scutellum to form an embryo-like structure, which leads to callus formation. Our transcriptome data show that embryo-, stem cell-, and auxin-related genes are upregulated during scutellum-derived callus initiation. Among those genes, the embryo-specific gene OsLEC1 is activated by auxin and involved in scutellum-derived callus initiation. However, OsLEC1 is not required for vasculature-derived callus initiation from roots. In addition, OsIAA11 and OsCRL1, which are involved in root development, are required for vasculature-derived callus formation but not for scutellum-derived callus formation. Overall, our data indicate that scutellum-derived callus initiation is regulated by an embryo-like development program, and this is different from vasculature-derived callus initiation which borrows a root development program.

Spatiotemporal variability and control factors of NO3- in a polluted karst water system of an agricultural wetland in South China.

Nitrate (NO3-) pollution in karst water is an important environmental issue in intensive agricultural regions worldwide. The integrated understanding of the spatiotemporal variability and control factors of NO3- pollution in karst water is imperative for controlling the diffuse pollution caused by agricultural activities. In this study, 49 water samples were collected from surface water (SW) and groundwater (GW) in the Huixian karst wetland (HKW) and analyzed using hydrogeochemical and isotopic data (δ18O-NO3-, δ15N-NO3- and δ13CDIC) in combination with a Bayesian mixing model to investigate the spatiotemporal distribution and control factors in NO3--polluted karst water. The results showed that approximately 40.82% of the karst water samples exceeded the natural threshold value of 3 mg/L for NO3--N, and 32.14% of the GW samples exceeded the permissible limit for drinking water established by WHO (10 mg/L as NO3--N), indicating that high levels of NO3- were mainly found in GW samples from the agricultural core area, especially in the dry season. The NH4+-synthetic fertilizer (NHF) and soil organic nitrogen (SON) were the dominant factors controlling pollution sources in the HKW, accounting for 36.13% ± 4.66% and 28.68% ± 4.75% of the karst GW NO3- concentration, respectively. However, the seasonal differences in NO3- pollution sources were not significant in GW. Microbial nitrification was the main process affecting the NO3- levels in GW, whereas the occurrence of denitrification did not significantly affect NO3- concentration in the HKW due to the relatively low rate. Moreover, the HNO3 produced from NH4+ via microbial nitrification facilitated carbonate weathering, thereby controlling NO3- enrichment in karst GW. Our results suggest that NHF should be controlled to prevent further GW pollution in the HKW. Our study also provides a scientific basis for understanding the factors controlling the NO3- concentrations in karst water systems.

OsHDA710-Mediated Histone Deacetylation Regulates Callus Formation of Rice Mature Embryo.

Histone deacetylases (HDACs) play important roles in the regulation of eukaryotic gene expression. The role of HDACs in specialized transcriptional regulation and biological processes is poorly understood. In this study, we evaluated the global expression patterns of genes related to epigenetic modifications during callus initiation in rice. We found that the repression of HDAC activity by trichostatin A (TSA) or by OsHDA710 mutation (hda710) results in impaired callus formation of rice mature embryo and increased global histone H3 acetylation levels. The HDAC inhibition decreased auxin response and cell proliferation in callus formation. Meanwhile, the transcriptional repressors OsARF18 and OsARF22 were upregulated in the callus of hda710. The chromatin immunoprecipitation-quantitative PCR (ChIP-qPCR) analysis demonstrated that the callus of hda710 exhibited enhanced histone H3 acetylation levels at the chromatin regions of OsARF18 and OsARF22. Furthermore, we found that OsARF18 and OsARF22 were regulated through OsHDA710 recruitment to their target loci. In addition, overexpression of OsARF18 decreased the transcription of downstream genes PLT1 and PLT2 and inhibited callus formation of the mature embryo. These results demonstrate that OsHDA710 regulates callus formation by suppressing repressive OsARFs via histone deacetylation during callus formation of rice mature embryo. This indicates that OsHDA710-mediated histone deacetylation is an epigenetic regulation pathway for maintaining auxin response during cell dedifferentiation.

Callus Initiation from Root Explants Employs Different Strategies in Rice and Arabidopsis.

Callus formation in tissue culture follows the rooting pathway, and newly formed callus seems to be a group of root primordium-like cells. However, it is not clear whether there are multiple mechanisms of callus initiation in different species and in different organs. Here we show that the OsIAA11-mediated pathway is specifically and strictly required for callus initiation in the lateral root (LR) formation region of the primary root (PR) but not for callus initiation at the root tip or the stem base in rice. OsIAA11 and its Arabidopsis homolog AtIAA14 are key players in lateral rooting. However, the AtIAA14-mediated pathway is not strictly required for callus initiation in the LR formation region in Arabidopsis. LRs can be initiated through either the AtIAA14-mediated or AtWOX11-mediated pathway in the Arabidopsis PR, therefore providing optional pathways for callus initiation. In contrast, OsIAA11 is strictly required for lateral rooting in the rice PR, meaning that the OsIAA11 pathway is the only choice for callus initiation. Our study suggests that multiple pathways may converge to WOX5 activation during callus formation in different organs and different species.

Effects of excitation area of longitudinal transducer on the flexural vibration characteristics of a rectangular plate in stripe mode.

The flexural vibration characteristics of a rectangular plate in stripe mode, driven at its center by a different longitudinal vibration ultrasonic transducer (LVUT) with different excitation area are investigated. The variation in the nodal lines and corresponding resonant frequency of the rectangular plate under different excitation area are calculated by using finite element method (FEM). The results show that the resonant frequency increases with the excitation area of the LVUT increasing, and the nodal lines bend obviously when the radius r of excitation area is greater than a certain value. The experimental tests are carried out by the aid of Polytec PSV-400 Scanning laser Vibrometer, and the results agree well those of numerically calculated. It indicates that the larger excitation area of longitudinal transducer may affect the ultrasonic field radiated by the rectangular plate.