A molecular framework for seasonal growth-dormancy regulation in perennial plants

The timing of the onset and release of dormancy impacts the survival,productivity and spatial distribution of temperate horticultural and forestry perennials and is mediated by at least three main regulatory programs involving signal perception and processing by phytochromes(PHYs)and PHY-interacting transcription factors(PIFs).PIF4 functions as a key regulator of plant growth in response to both external and internal signals.In poplar,the expression of PIF4 and PIF3-LIKE1 is upregulated in response to short days,while PHYA and PHYB are not regulated at the transcriptional level.Integration of light and environmental signals is achieved by gating the expression and transcriptional activity of PIF4.During this annual cycle,auxin promotes the degradation of Aux/IAA transcriptional repressors through the SKP–Cullin-F–boxTIR1 complex,relieving the repression of auxin-responsive genes by allowing auxin response factors(ARFs)to activate the transcription of auxin-responsive genes involved in growth responses.Analyses of transcriptome changes during dormancy transitions have identified MADS-box transcription factors associated with endodormancy induction.Previous studies show that poplar dormancy-associated MADS-box(DAM)genes PtMADS7 and PtMADS21 are differentially regulated during the growth-dormancy cycle.Endodormancy may be regulated by internal factors,which are specifically localized in buds.PtMADS7/PtMADS21 may function as an internal regulator in poplar.The control of flowering time shares certain regulatory hierarchies with control of the dormancy/growth cycle.However,the particularities of different stages of the dormancy/growth cycle warrant comprehensive approaches to identify the causative genes for the entire cycle.A growing body of knowledge also indicates epigenetic regulation plays a role in these processes in perennial horticultural and forestry plants.The increased knowledge contributes to better understanding of the dormancy process and consequently to precise manipulation of dormancy-related horticultural traits,such as flowering time.

The Conserved Proline Residue in the LOB Domain of LBD18 Is Critical for DNA-Binding and Biological Function

Dear Editor, The LATERAL ORGAN BOUNDARIES DOMAIN （LBD）/ ASYMMETRICLEAVES2-LIKE （ASL） genes （hereafter referred to as LBD） encode proteins containing a conserved plant-specific LOB domain and play roles in lateral organ development （Iwakawa et al., 2002; Shuai et al., 2002; Majer and Hochholdinger, 2011）. The LOB domain is approximately 100 amino acids in length and contains a conserved four-Cys motif （CX2CX6CX3C）, the Gly-Ala-Ser block （GAS）, and the leucine-zipper-like coiled-coil motif （LX6LX3LX6L） （Shuai et al., 2002）. The leucine-zipper-like coiled-coil motif in the LOB domain is predicted to function in protein dimerization. LOB, AS2, and LBD4 preferentially bind unique DNA sequences in electrophoretic mobility shift assays （EMSAs） （Husbands et al., 2007）. The LOB domain of AS2 cannot be functionally replaced by those of other members of the LOB family,

MYB46-Mediated Transcriptional Regulation of Secondary Wall Biosynthesis

Formation of secondary wall requires coordinated transcrip- tional regulation of the genes involved in the biosynthesis of major secondary wall components （e.g. cellulose, hemicellu- lose, and lignin）. Even though many aspects of plant biology have been extensively elucidated using various model spe- cies, our current understanding of secondary wall formation is limited.