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Phased small-interfering RNAs (phasiRNAs) are a special class of small RNAs, which are generated in 21- or 24-nt intervals from transcripts of precursor RNAs. Although phasiRNAs have been found in a range of organisms, their biological functions in plants have yet to be uncovered. Here we show that phasiRNAs generated by the photopheriod-sensetive genic male sterility 1 (Pms1) locus were associated with photoperiod-sensitive male sterility (PSMS) in rice, a germplasm that started the two-line hybrid rice breeding. The Pms1 locus encodes a long-noncoding RNA PMS1T that was preferentially expressed in young panicles. PMS1T was targeted by miR2118 to produce 21-nt phasiRNAs that preferentially accumulated in the PSMS line under long-day conditions. A single nucleotide polymorphism in PMS1T nearby the miR2118 recognition site was critical for fertility change, likely leading to differential accumulation of the phasiRNAs. This result suggested possible roles of phasiRNAs in reproductive development of rice, demonstrating the potential importance of this RNA class as regulators in biological processes. [ABSTRACT FROM AUTHOR]

Nitric oxide (NO), an active signaling molecule in plants, is involved in numerous physiological processes and adaptive responses to environmental stresses. Under high-salt conditions, plants accumulate NO quickly, and reorganize Na+ and K+ contents. However, the molecular connection between NO and ion homeostasis is largely unknown. Here, we report that NO lowers K+ channel AKT1-mediated plant K+ uptake by modulating vitamin B6 biosynthesis. In a screen for Arabidopsis NO-hypersensitive mutants, we isolated sno1 (sensitive to nitric oxide 1), which is allelic to the previously noted mutant sos4 (salt overly sensitive 4) that has impaired Na+ and K+ contents and overproduces pyridoxal 5'-phosphate (PLP), an active form of vitamin B6. We showed that NO increased PLP and decreased K+ levels in plant. NO induced SNO1 gene expression and enzyme activity, indicating that NO-triggered PLP accumulation mainly occurs through SNO1-mediated vitamin B6 salvage biosynthetic pathway. Furthermore, we demonstrated that PLP significantly repressed the activity of K+ channel AKT1 in the Xenopus oocyte system and Arabidopsis root protoplasts. Together, our results suggest that NO decreases K+ absorption by promoting the synthesis of vitamin B6 PLP, which further represses the activity of K+ channel AKT1 in Arabidopsis. These findings reveal a previously unidentified pivotal role of NO in modulating the homeostasis of vitamin B6 and potassium nutrition in plants, and shed light on the mechanism of NO in plant acclimation to environmental changes. [ABSTRACT FROM AUTHOR]

Circadian clocks are ubiquitous molecular time-keeping mechanisms that coordinate physiology and metabolism and provide an adaptive advantage to higher plants. The central oscillator of the plant clock is composed of interlocked feedback loops that involve multiple repressive factors acting throughout the circadian cycle. PSEUDO RESPONSE REGULATORS (PRRs) comprise a five-member family that is essential to the function of the central oscillator. PRR5, PRR7, and PRR9 can bind the promoters of the core clock genes CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY) to restrict their expression to near dawn, but the mechanism has been unclear. Here we report that members of the plant Groucho/Tup1 corepressor family, TOPLESS/TOPLESS-RELATED (TPL/TPR), interact with these three PRR proteins at the CCA1 and LHY promoters to repress transcription and alter circadian period. This activity is diminished in the presence of the inhibitor trichostatin A, indicating the requirement of histone deacetylase for full TPL activity. Additionally, a complex of PRR9, TPL, and histone deacetylase 6, can form in vivo, implicating this tripartite association as a central repressor of circadian gene expression. Our findings show that the TPL/TPR corepressor family are components of the central circadian oscillator mechanism and reinforces the role of this family as central to multiple signaling pathways in higher plants. [ABSTRACT FROM AUTHOR]