RICHARD SCOTT POETHIG

..Thus, in Arabidopsis, CyP40 is specifically required for the vegetative but not the reproductive maturation of the shoot...

..Small RNAs have also been shown to play a role in the transition between different stages of gametophyte development in the moss Physcomitrella patens. The use of small RNAs for temporal regulation is therefore quite ancient in plants...

..Our results indicate that FBW2 is a novel negative regulator of AGO1 and suggest that it plays a role in ABA signalling and/or response...

..Coordination of these processes is accomplished in part by a thermal clock and by signal transduction pathways that mediate the response of plants to light...

..Our results define the core components of a post-transcriptional gene silencing pathway in Arabidopsis and reveal some of the features that direct transcripts to this pathway...

..miR156 and miR172 are positively regulated by the transcription factors they target, suggesting that negative feedback loops contribute to the stability of the juvenile and adult phases...

..Moreover, the identified SPL activity defines a distinct pathway in control of this vital developmental decision...

..This has led to the identification of a new class of short interfering RNAs (siRNAs) called trans-acting siRNAs (ta-siRNAs)...

..We conclude that vegetative phase change in Arabidopsis is regulated by an increase in the expression of SPL3 and probably also SPL4 and SPL5, and that this increase is a consequence of a decrease in the level of miR156...

..Genetic backgrounds that enhance the mutant phenotype of epc demonstrate that, in addition to its role in phase change, epc is required for the maintenance of the shoot apical meristem, leaf initiation, and root initiation...

..These results demonstrate that KAN1 acts as a transcriptional repressor and that mutually repressive interactions between KAN1 and AS2 contribute to the establishment of adaxial-abaxial polarity in plants...

..The hst loss-of-function phenotype suggests that this protein regulates the nucleocytoplasmic transport of molecules involved in several different morphogenetic pathways, as well as molecules generally required for root and shoot growth...

..We propose that the mutant phenotype of psd reflects defects in developmental events and cell/tissue types that require elevated levels of protein synthesis and are therefore acutely sensitive to a reduction in tRNA export...

..This work has lead to a reexamination of many previously characterized mutations that are now known to affect components or targets of miRNA-mediated pathways...

..Although the targets of these miRNAs are still not known, excellent candidates have been identified based on sequence similarity to the miRNAs...

..These results demonstrate that HST and PSD do not share RNA cargos in nuclear export and strongly suggest that there are multiple nuclear export pathways for these small RNAs in Arabidopsis...

..Our results suggest that AGO1, or an AGO1-interacting protein, is a major client of CyP40 and that miR156 and its targets play a central role in the regulation of vegetative phase change in Arabidopsis...

..In this issue of Developmental Cell, Gazzarrini et al. show that FUSCA3 plays a critical role in regulating hormone levels to synchronize the transition from embryonic to vegetative growth in Arabidopsis...

..Their mutant phenotype reveals the existence of a previously unknown temporal regulatory mechanism in plant embryogenesis...

..In addition to these conserved miRNAs, there are many clade and species-specific miRNAs, which have evolved more recently and whose functions are currently unknown...

..The research described here will reveal the role of PTGS in temporal regulation in plants, and will contribute to future studies of the mechanism of this process in both plants and animals. ..

..A better understanding of the fundamental mechanism of developmental timing, and the role of small RNAs in this process, is essential for developing therapies for these problems in human health and development. ..