Identification of novel cis-elements bound by BplMYB46 involved in abiotic stress responses and secondary wall deposition

Transcription factors （TFs） play vital roles in various biological processes by binding to cis-acting elements to control expressions of their target genes. The MYB TF BplMYB46, from Betula platyphylla, is involved in abiotic stress responses and secondary wall deposition. In the present study, we used a TF-centered yeast onehybrid technology （TF-centered YIH） to identify the cis- acting elements bound by BplMYB46. We screened a shortinsert random library and identified three cis-elements bound by BplMYB46： an E-box （CA（A/T/C）（A/G/C）TG） and two novel motifs, a TO-box （T（GIA）TCG（C/G）） and a GT-box （A（G/T）T（AIC）GT（T/G）C）. Chromatin immunoprecipitation （CHIP） and effector-reporter coexpression assays inNicotiana tabacum confirmed binding of BplMYB46 to the TC-box, GT-box, and E-box motifs in the promoters of the phenylalanine ammonia lyase （PAL）, peroxidase （POD）, and superoxide dismutase （SOD） genes, which function in abiotic stress tolerance and secondary wall biosynthesis. This finding improves our understanding of potential regulatory mechanisms in the response to abiotic stress and secondary wall deposition of BplMYB46 in B. platyphylla.

Thermal-structural response and low-cycle fatigue damage of channel wall nozzle

To investigate the thermo-mechanical response of channel wall nozzle under cyclic working loads,the fnite volume fluid-thermal coupling calculation method and the fnite element thermal-structural coupling analysis technique are applied.In combination with the material lowcycle fatigue behavior,the modifed continuous damage model on the basics of local strain approach is adopted to analyze the fatigue damage distribution and accumulation with increasing nozzle work cycles.Simulation results have shown that the variation of the non-uniform temperature distribution of channel wall nozzle during cyclic work plays a signifcant role in the thermal-structural response by altering the material properties;the thermal-mechanical loads interaction results in serious deformation mainly in the front region of slotted liner.In particular,the maximal cyclic strains appear in the intersecting regions of liner gas side wall and symmetric planes of channel and rib,where the fatigue failure takes place initially;with the increase in nozzle work cycles,the residual plastic strain accumulates linearly,and the strain amplitude and increment in each work cycle are separately equal,but the fatigue damage grows up nonlinearly.As a result,a simplifed nonlinear damage accumulation approach has been suggested to estimate the fatigue service life of channel wall nozzle.The predicted node life is obviously conservative to the Miner＇s life.In addition,several workable methods have also been proposed to improve the channel wall nozzle durability.