Expression of PaNAC01, a Picea abies CUP-SHAPED COTYLEDON orthologue, is regulated by polar auxin transport and associated with differentiation of the shoot apical meristem and formation of separated cotyledons.
OBJECTIVE
During embryo development in most gymnosperms, the establishment of the shoot apical meristem (SAM) occurs concomitantly with the formation of a crown of cotyledons surrounding the SAM. It has previously been shown that the differentiation of cotyledons in somatic embryos of Picea abies is dependent on polar auxin transport (PAT). In the angiosperm model plant, Arabidopsis thaliana, the establishment of cotyledonary boundaries and the embryonal SAM is dependent on PAT and the expression of the CUP-SHAPED COTYLEDON (CUC) genes, which belong to the large NAC gene family. The aim of this study was to characterize CUC-like genes in a gymnosperm, and to elucidate their expression during SAM and cotyledon differentiation, and in response to PAT.


METHODS
Sixteen Picea glauca NAC sequences were identified in GenBank and deployed to different clades within the NAC gene family using maximum parsimony analysis and Bayesian inference. Motifs conserved between angiosperms and gymnosperms were analysed using the motif discovery tool MEME. Expression profiles during embryo development were produced using quantitative real-time PCR. Protein conservation was analysed by introducing a P. abies CUC orthologue into the A. thaliana cuc1cuc2 double mutant.


RESULTS
Two full-length CUC-like cDNAs denoted PaNAC01 and PaNAC02 were cloned from P. abies. PaNAC01, but not PaNAC02, harbours previously characterized functional motifs in CUC1 and CUC2. The expression profile of PaNAC01 showed that the gene is PAT regulated and associated with SAM differentiation and cotyledon formation. Furthermore, PaNAC01 could functionally substitute for CUC2 in the A. thaliana cuc1cuc2 double mutant.


CONCLUSIONS
The results show that CUC-like genes with distinct signature motifs existed before the separation of angiosperms and gymnosperms approx. 300 million years ago, and suggest a conserved function between PaNAC01 and CUC1/CUC2.
Department of Plant Biology and Forest Genetics, Linnean Centre of Plant Biology in Uppsala, Uppsala BioCenter, Swedish University of Agricultural Sciences, Uppsala, Sweden. emma.larsson@slu.se
Emma
E
Larsson
Jens F
JF
Sundström
Folke
F
Sitbon
Sara
S
von Arnold
D020816:Amino Acid Motifs; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D001692:Biological Transport; D002454:Cell Differentiation / Q000235:genetics; D019295:Computational Biology; D018548:Cotyledon / Q000166:cytology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000235:genetics*; D007210:Indoleacetic Acids / Q000378:metabolism*; D018519:Meristem / Q000166:cytology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D005810:Multigene Family; D009154:Mutation; D010641:Phenotype; D010802:Phylogeny; D028222:Picea / Q000166:cytology / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D010937:Plant Growth Regulators / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics; D036226:Seedlings / Q000166:cytology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D012639:Seeds / Q000166:cytology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism
D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D010940:Plant Proteins