Callus proliferation-induced hypoxic microenvironment decreases shoot regeneration competence in Arabidopsis

Plants are aerobic organisms that rely on molecular oxygen for respiratory energy production.Hypoxic conditions,with oxygen levels ranging between 1%and 5%,usually limit aerobic respiration and affect plant growth and development.Here,we demonstrate that the hypoxic microenvironment induced by active cell proliferation during the two-step plant regeneration process intrinsically represses the regener-ation competence of the callus in Arabidopsis thaliana.We showed that hypoxia-repressed plant regener-ation is mediated by the RELATED TO APETALA2.12(RAP2.12)protein,a memberof the Ethylene Response Factor VIl(ERF-Vll)family.We found that the hypoxia-activated RAP2.12 protein promotes salicylic acid(SA)biosynthesis and defense responses,thereby inhibiting pluripotency acquisition and de novo shoot regeneration in calli.Molecular and genetic analyses revealed that RAP2.12 could bind directly to the SALICYLIC ACID INDUCTION DEFICIENT 2(SID2)gene promoter and activate SA biosynthesis,repressing plant regeneration possibly via a PLETHORA(PLT)-dependent pathway.Consistently,the rap2.12 mutant calli exhibits enhanced shoot regeneration,which is impaired by SA treatment.Taken together,these find-ings uncover that the cell proliferation-dependent hypoxic microenvironment reduces cellular pluripotency and plant regeneration through the RAP2.12-SID2 module.

Functional expression of a proliferation-related ligand in hepatocellular carcinoma and its implications for neovascularization

AIM： To detect the expression of a proliferation-related ligand on human hepatocellular carcinoma （HCC） cell lines （SK-Hepl, HLE and HepG2） and in culture medium. METHODS： APRIL expression was analyzed by Western blotting in HCC cell lines. Effects of APRIL to cell count and angiogenesis were analyzed, too. RESULTS： Recombinant human APRIL （rhAPRIL） increased cell viability of HepG2 cells and, in HUVEC, rhAPRIL provided slight tolerance to cell death from serum starvation. Soluble APRIL （sAPRIL） from HLE cells increased after serum starvation, but did not change in SK-Hepl or HepG2 cells. These cells showed down-regulation of VEGF after incubation with anti-APRIL antibody. Furthermore, culture medium from the HCC cells treated with anti-APRIL antibody treatment inhibited tube formation of HUVECs. CONCLUSION： Functional expression of APRIL might contribute to neovascularization via an upregulation of VEGF in HCC.