[The regulatory roles of small RNAs in phytohormone signaling pathways].

Phytohormones are signaling molecules that control plant growth and development. Recent studies revealed that non-coding small RNAs play critical roles in plant development and stress responses via phytohormone signaling pathways. In this review, we summarize the present knowledge on the microRNAs (miRNAs) and secondary short interfering RNAs (siRNAs) involved in phytohormone signaling pathways, which include auxin, gibberellic acid, brassinosteroid and abscisic acid pathways. We also discuss their possible implications in phytohormone crosstalk during specific developmental processes.

Progress on the autophagic regulators and receptors in plants.

Autophagy is an evolutionarily highly conserved catabolic pathway among eukaryotic cells that protects the organisms against environmental stress. Normally, autophagy is mainly involved with autophagy-related proteins(ATGs) and autophagic regulators including a series of cytoplasmic proteins and small molecules. Besides, the selective autophagy, which targets damaged organalles or protein aggregates, is mediated by the additional receptors to help the ATGs recognize different substrates. In this review, we summarize recent advances in autophagic regulators like ROS(Reactive oxygen species), TOR(Target of rapamycin) and receptors like NBR1(Neighbor of BRCA1 gene protein), RPN10(Regulatory particle non-ATPase 10) as well as their functional mechanisms mainly in Arabidopsis thaliana.

Association of specific pectin methylesterases with Al-induced root elongation inhibition in rice.

The negative charges of cell wall pectin molecules attributed by pectin methylesterase (PME, EC 3.1.1.11) contribute to Al binding capacity. We examined the expression profiles of 35 members of the PME gene family in the root apex of an Al-sensitive rice 'Zhefu802' under Al stress. While root elongation was inhibited by 40% after 3-h exposure to 25 µM Al, cell wall PME activity and the abundance of eight PME genes transcripts were increased. The same Al treatment which had almost no effect on root elongation of an Al-resistant rice ssp. japonica 'Nipponbare' did not change the expression patterns of these eight PME genes. However, when Al concentration was increased to 50 µM, by which the root elongation of 'Nipponbare' was inhibited by 40% too, the expression of these PME genes were also upregulated except two genes with no signal. These suggest a possible correlation between the upregulated genes and Al-induced inhibition of root elongation in rice. Furthermore, these eight PME genes behaved differently when subjected to CdCl2 and LaCl3 treatments, implying the specificity of different PME genes in response to different metal toxicities. The transgenic rice overexpressing one of these eight PME genes OsPME14 showed higher PME activity and Al content in root tip cell wall, and became more sensitive to Al stress, verifying the involvement of the specific PME gene in Al toxicity. Therefore, our results provided the molecular evidence to connect the expression of specific PME genes with the Al-induced inhibition of root elongation in rice.

[Recent advances in the techniques of protein-protein interaction study].

Protein-protein interactions play key roles in the development of organisms and the response to biotic and abiotic stresses. Several wet-lab methods have been developed to study this challenging area,including yeast two-hybrid system, tandem affinity purification, Co-immunoprecipitation, GST Pull-down, bimolecular fluorescence complementation, fluorescence resonance energy transfer and surface plasmon resonance analysis. In this review, we discuss theoretical principles and relative advantages and disvantages of these techniques,with an emphasis on recent advances to compensate for limitations.

[Recent research progress of biogenesis and functions of miRNA*].

MicroRNA*s are about 22nt noncoding RNAs, which are processed from precursors with a characteristic hairpin secondary structure in the biogenesis of microRNAs. Recently, miRNA* strands were shown to mediate post-transcriptional regulatory networks, rather than serve merely as non-functional by-product in general view. Unlike miRNAs bound to AGO1, miRNA* strands are bound to AGO2 to form RISC duplex to mediate RNAi, which is similar to siRNA. This paper mainly reviewed the recent research progresses on miRNA*, such as the biosynthesis, biological characteristics, and functions.

Regulation of auxin response by miR393-targeted transport inhibitor response protein 1 is involved in normal development in Arabidopsis.

miR393, which is encoded by MIR393a and MIR393b in Arabidopsis, post-transcriptionally regulates mRNAs for the F-box auxin receptors TIR1 (Transport Inhibitor Response Protein 1), AFB1 (Auxin Signaling F-box Protein 1), AFB2 and AFB3. However, biological functions of the miR393-TIR1/AFBs module in auxin response and plant development is not fully understood. In the study herein, we demonstrate that miR393 accumulated in response to exogenous IAA treatment, and its induction was due to enhanced MIR393b transcription but not MIR393a. Overexpression of a miR393-resistant form of TIR1 (mTIR1) enhanced auxin sensitivity and led to pleiotropic effects on plant development including inhibition of primary root growth, overproduction of lateral roots, altered leave phenotype and delayed flowering. Furthermore, miR393 level was increased in 35S:mTIR1 plant, suggesting that TIR1 promoted the expression of miR393 by a feedback loop. The interaction between miR393 and its target indicates a fine adjustment to the roles of the miR393-TIR1 module, which is required for auxin responses in plant development.

Identification and characterization of two bamboo (Phyllostachys praecox) AP1/SQUA-like MADS-box genes during floral transition.

Bamboo (Bambusoideae) is by far the largest member of the grass family Poaceae, which is vital to the economy of many countries in the tropics and subtropics. However, the mechanism of flowering of bamboo (Phyllostachys praecox) is still unknown. In this study, we isolated two novel genes from P. praecox and evaluated their functional characteristics. The sequence and phylogenetic analysis indicated that these two genes, named PpMADS1 and PpMADS2, belong to FUL3 and FUL1 clade of Poaceae AP1/SQUA-like genes, respectively. The PpMADS2 possesses a truncated C terminus lacking the highly conserved paleoAP1 motif. It was further confirmed that the truncated C-terminal region was produced by natural sequence deletion in exons, but not by alternative splicing. Ectopic expression of PpMADS1 and PpMADS2 significantly promoted early flowering through upregulation of AP1 in Arabidopsis. Yeast two-hybrid experiments demonstrated that AP1 protein can interact with PpMADS1 but not PpMADS2, suggesting that these two genes may act differently in signaling early flowering of bamboo plants. RT-qPCR and in situ hybridization analysis revealed distinct expression patterns of these two genes in vegetative and reproductive tissues of bamboo. Taken together, our results suggest that both PpMADS1 and PpMADS2 are involved in floral transition, and PpMADS2 might play more important roles than PpMADS1 in floral development of Phyllostachys praecox.

Regulation of flowering time via miR172-mediated APETALA2-like expression in ornamental gloxinia (Sinningia speciosa).

We investigated the microRNA172 (miR172)-mediated regulatory network for the perception of changes in external and endogenous signals to identify a universally applicable floral regulation system in ornamental plants, manipulation of which could be economically beneficial. Transgenic gloxinia plants, in which miR172 was either overexpressed or suppressed, were generated using Agrobacterium-mediated transformation. They were used to study the effect of altering the expression of this miRNA on time of flowering and to identify its mRNA target. Early or late flowering was observed in transgenic plants in which miR172 was overexpressed or suppressed, respectively. A full-length complementary DNA (cDNA) of gloxinia (Sinningia speciosa) APETALA2-like (SsAP2-like) was identified as a target of miR172. The altered expression levels of miR172 caused up- or down-regulation of SsAP2-like during flower development, which affected the time of flowering. Quantitative real-time reverse transcription PCR analysis of different gloxinia tissues revealed that the accumulation of SsAP2-like was negatively correlated with the expression of miR172a, whereas the expression pattern of miR172a was negatively correlated with that of miR156a. Our results suggest that transgenic manipulation of miR172 could be used as a universal strategy for regulating time of flowering in ornamental plants.

Protective effects of ETC complex III and cytochrome c against hydrogen peroxide-induced apoptosis in yeast.

In mammals, the mitochondrial electron transfer components (ETC) complex III and cytochrome c (cyt c) play essential roles in reactive oxygen species (ROS)-induced apoptosis. However, in yeast, the functions of cyt c and other ETC components remain unclear. In this study, three ETC-defective yeast mutants qcr7Δ, cyc1Δcyc7Δ, and cox12Δ, lacking cyt c oxidoreductase (complex III), cyt c, and cyt c oxidase (complex IV), respectively, were used to test the roles of these proteins in the response of cells to hydrogen peroxide (H2O2). Mutants qcr7Δ and cyc1Δcyc7Δ displayed greater H2O2 sensitivity than the wild-type or cox12Δ mutant. Consistent with this, qcr7Δ and cyc1Δcyc7Δ produced higher ROS levels, displayed derepressed expression of the proapoptotic genes AIF1, NUC1, and NMA111, but not YCA1, at the mRNA level, and were more vulnerable to H2O2-induced apoptosis. Interestingly, mutants lacking these proapoptotic genes displayed enhanced H2O2 tolerance, but unaffected ROS accumulation. Furthermore, the overexpression of antiapoptotic genes (Bcl-2, Ced-9, AtBI-1, and PpBI-1) reduced the levels of AIF1, NUC1, and NMA111 mRNAs, and reduced H2O2-induced cell death. Our findings identify two ETC components as early-inhibitory members of the ROS-mediated apoptotic pathway, suggesting their essential roles in metabolizing H2O2, probably by providing reduced cyt c, allowing cyt c peroxidase to remove H2O2 from the cells.

Overexpression of the cucumber LEAFY homolog CFL and hormone treatments alter flower development in gloxinia (Sinningia speciosa).

Leafy (LFY) and LFY-like genes control the initiation of floral meristems and regulate MADS-box genes in higher plants. The Cucumber-FLO-LFY (CFL) gene, a LFY homolog in Cucumis sativus L. is expressed in the primordia, floral primordia, and each whirl of floral organs during the early stage of flower development. In this study, functions of CFL in flower development were investigated by overexpressing the CFL gene in gloxinia (Sinningia speciosa). Our results show that constitutive CFL overexpression significantly promote early flowering without gibberellin (GA(3)) supplement, suggesting that CFL can serve functionally as a LFY homolog in gloxinia. Moreover, GA(3) and abscisic acid (ABA) treatments could modulate the expression of MADS-box genes in opposite directions. GA(3) resembles the overexpression of CFL in the expression of MADS-box genes and the regeneration of floral buds, but ABA inhibits the expression of MADS-box genes and flower development. These results suggest that CFL and downstream MADS-box genes involved in flower development are regulated by GA(3) and ABA.

Programmed cell death-involved aluminum toxicity in yeast alleviated by antiapoptotic members with decreased calcium signals.

The molecular mechanisms of aluminum (Al) toxicity and tolerance in plants have been the focus of ongoing research in the area of stress phytophysiology. Recent studies have described Al-induced apoptosis-like cell death in plant and animal cells. In this study, we show that yeast (Saccharomyces cerevisiae) exposed to low effective concentrations of Al for short times undergoes enhanced cell division in a manner that is dose and cell density dependent. At higher concentrations of Al or longer exposure times, Al induces cell death and growth inhibition. Several apoptotic features appear during Al treatment, including cell shrinkage, vacuolation, chromatin marginalization, nuclear fragmentation, DNA degradation, and DNA strand breaks, as well as concomitant cell aggregation. Yeast strains expressing Ced-9, Bcl-2, and PpBI-1 (a plant Bax inhibitor-1 isolated from Phyllostachys praecox), respectively, display more resistance to Al toxicity compared with control cells. Data from flow cytometric studies show these three antiapoptotic members do not affect reactive oxygen species levels, but decrease calcium ion (Ca(2+)) signals in response to Al stress, although both intracellular reactive oxygen species and Ca(2+) levels were increased. The data presented suggest that manipulation of the negative regulation process of programmed cell death may provide a novel mechanism for conferring Al tolerance.