SUMMARY microRNAs (miRNAs) play important roles in plant growth and development. Previous studies have shown that down-regulation of miR398 in response to oxidative stress permits up-regulation of one of its target genes, CSD2 (copper/zinc superoxide dismutase), and thereby helps plants to cope with oxidative stress. We report here that heat stress rapidly induces miR398 and reduces transcripts of its target genes CSD1, CSD2 and CCS (a gene encoding a copper chaperone for both CSD1 and CSD2). Transgenic plants expressing miR398-resistant forms of CSD1, CSD2 and CCS under the control of their native promoters are more sensitive to heat stress (as indicated by increased damage at the whole-plant level and to flowers) than transgenic plants expressing normal coding sequences of CSD1, CSD2 or CCS under the control of their native promoters. In contrast, csd1, csd2 and ccs mutant plants are more heat-tolerant (as indicated by less damage to flowers) than the wild-type. Expression of genes encoding heat stress transcription factors (HSF genes) and heat shock proteins (HSP genes) is reduced in heat-sensitive transgenic plants expressing miR398-resistant forms of CSD1, CSD2 or CCS but is enhanced in the heat-tolerant csd1, csd2 and ccs plants. Chromatin immunoprecipitation assays revealed that HSFA1b and HSFA7b are the two HSFs responsible for heat induction of miR398. Together, our results suggest that plants use a previously unrecognized strategy to achieve thermotolerance, especially for the protection of reproductive tissues. This strategy involves the down-regulation of CSD genes and their copper chaperone CCS through heat-inducible miR398.

The cyclic nucleotides, cAMP and cGMP, are the key molecules controlling mammalian oocyte meiosis. Their roles in oocyte biology have been at the forefront of oocyte research for decades, and many of the long-standing controversies in relation to the regulation of oocyte meiotic maturation are now resolved. It is now clear that the follicle prevents meiotic resumption through the actions of natriuretic peptides and cGMP -inhibiting the hydrolysis of intra-oocyte cAMP -and that the pre-ovulatory gonadotrophin surge reverses these processes.

Heat stress is a major environmental constraint for crop production worldwide. To respond to and cope with heat stress, plants synthesize heat shock proteins (HSPs), which are often molecular chaperones and are under the control of heat stress transcription factors (HSFs). Very little is known about the upstream regulators of HSFs. In a forward genetic screen for regulators of C-REPEAT BINDING FACTOR (CBF) gene expression (RCFs), we identified RCF2 and found that it is allelic to CPL1/FIERY2, which encodes a homolog of C-terminal domain phosphatase. Our results also showed that, in addition to being critical for cold stress tolerance, RCF2 is required for heat stress-responsive gene regulation and thermotolerance, because, compared with the wild type, the rcf2-1 mutant is hypersensitive to heat stress and because the reduced thermotolerance is correlated with lower expression of most of the 21 HSFs and some of the HSPs in the mutant plants. We found that RCF2 interacts with the NAC transcription factor NAC019 and that RCF2 dephosphorylates NAC019 in vivo. The nac019 mutant is more sensitive to heat stress than the wild type, and chromatin immunoprecipitation followed by quantitative PCR analysis revealed that NAC019 binds to the promoters of HSFA1b, HSFA6b, HSFA7a, and HSFC1. Overexpression of RCF2 or NAC019 in Arabidopsis thaliana increases thermotolerance. Together, our results suggest that, through dephosphorylation of NAC019, RCF2 is an integrator of high-temperature signal transduction and a mechanism for HSF and HSP activation.

Low mtDNA and ATP content might contribute to the absence of birefringent spindle imaged with the PolScope in human in vitro matured oocytes.

Combined treatment of cilostamide and forskolin positively influences oocyte developmental competence by exhibiting a synergistic effect on the prevention of GJC loss and resumption of meiosis.