Abstract
Anthocyanin biosynthesis and accumulation is closely associated with tissue/organ coloring in plants. To gain insight into the physiological and molecular mechanisms of leaf coloring in Acer palmatum, a deciduous tree during autumnal senescence, we first investigated concentration dynamics of pigments (i.e., chlorophyll, carotenoid and anthocyanin) in leaves with differential coloring. It was found that compared to green leaves (GN), anthocyanins were accumulated actively in semi-red (SR) and total-red (TR) leaves, accompanied with chlorophyll and carotenoid degradation. Then transcriptional profiling on GN and SR leaves identified thousands of transcripts with differential expression in SR compared to GN leaves. An annotation search showed that the entire flavonoid/anthocyanin biosynthesis pathway from the production of naringenin chalcone to modification of flavonoid backbone was extensively activated at the transcriptional level in SR leaves. Phylogenetic analysis of putative MYB proteins identified ApMYB1 as a putative regulator promoting anthocyanin biosynthesis. Expression of ApMYB1 in leaves was induced by exogenous hormones including abscisic acid. Stable overexpression of ApMYB1 in tobacco resulted in leaves with higher accumulation of anthocyanins. Collectively, our results identified ApMYB1 as a positive regulator associated with leaf coloring in Acer palmatum during autumnal senescence, which may be regarded a potential target for breeding color-leafed plants.
Highlights
For deciduous trees with autumnal leaf coloring, two physiological components are essential: chlorophyll degradation and/or anthocyanin biosynthesis, both of which mainly happen during leaf senescence [1]
How abscisic acid (ABA) or ethylene is involved in leaf coloring of deciduous trees remains elusive. These data indicated that ApMYB1, as a typical R2R3-type MYB transcription factor, is responsive to both developmental and hormonal signals and may act as a positive regulator of anthocyanin biosynthesis during leaf coloring in Acer palmatum
This study provided a valuable basis for further elucidating mechanisms of coloration of Acer palmatum leaves during autumnal senescence
Summary
For deciduous trees with autumnal leaf coloring, two physiological components are essential: chlorophyll degradation and/or anthocyanin biosynthesis, both of which mainly happen during leaf senescence [1]. The wellknown MBW regulatory complex, which consists of DNA-binding R2R3 MYB transcription factors and MYC-like basic helix-loop-helix (bHLH) and WD40-repeat proteins, has been identified to regulate structural genes of anthocyanin biosynthesis in multiple species [9–11]. Ectopic expression of a R2R3 MYB transcription factor NtMYB2 from Chinese narcissus (Narcissus tazetta L.) in tobacco significantly reduced the floral pigmentation by repressing transcript levels of UFGT [20] Both positive and negative MYB proteins together may allow fine-tuning of anthocyanin biosynthesis in various tissue types and in response to developmental, environmental, and hormonal cues. TTohemeoxdpirfeiscsaitoinonlevoeflsflavonoiodf b2a0cskebleocnteedwtraasnesxcrtiepntssivinelGyNacatnivdaSteRdpautttahtievetrlyaninscvroilpvteidoninalfllaevvoenl oinidS/Ranltehaovceysa.nTinhe exbiosynthesis were measured by qPCR and results confirmed their up-regulation in SR pression levels of 20 selected transcripts in GN and SR putatively involved in flavonoid/anthocyanin biosynthesis were measured by qPCR and results confirmed their up-regulation in SR leaves (Supplementary Figure S1), being consistent with RNA-seq data (Supplementary Table S3). MobYtaBi1netdhebreyafatleigr)nisngenpcleopsteideinsetqhueednacsehseodfreacllta4n2gdlei.ffTehreenitniatallcyt pexhpyrleosgseendetMicYtrBeetrwanasscoribpttasinweidthby aelliegvneinngrepfeerpetnidcee MseYquBesnwceitshokfnaollw4n2 dfuifnfcetrieonntioafllpyreoxmporetisnsgedflMavYonBotirda/nasnctrhipoctsyawniitnh beiloesvyennthreefseisreinnce MArYaBbisdowpistihs tkhnaoliwanna f(uAntc),tiVointios fvpinriofemrao(tVinvg),flMavaolunsodido/maensttihcaoc(yMadn)in, Cbiitorusysnstinheenssisisin(CAs)r,abPirduonpusissatmhaelriai-na (cAant)a, (VPiatims v)iannifderPao(pVuvl)u,sMtraicluhsocdaormpaes(tPicta).(Md), Citrus sinensis (Cs), Prunus americana (Pam) and Populus trichocarpa (Pt)
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