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Plant Cell Physiol. 2015 Apr;56(4):700-14. doi: 10.1093/pcp/pcu215. Epub 2015 Jan 9.

Comprehensive genome-wide analysis of the Aux/IAA gene family in Eucalyptus: evidence for the role of EgrIAA4 in wood formation.

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LRSV Laboratoire de Recherche en Sciences Végétales, UMR5546, Université Toulouse III, UPS, CNRS, BP 42617, Auzeville, F-31326 Castanet Tolosan, France.
Université de Toulouse, INP-ENSA Toulouse, Génomique et Biotechnologie des Fruits, Avenue de l'Agrobiopole BP 32607, F-31326 Castanet-Tolosan, France INRA, UMR990 Génomique et Biotechnologie des Fruits, Chemin de Borde Rouge, F-31326 Castanet-Tolosan, France.
Instituto de Investigação Científica e Tropical (IICT/MNE), Palácio Burnay, Rua da Junqueira, 30, 1349-007 Lisboa, Portugal IBET - Instituto de Biologia Experimental e Tecnológica, Apartado 12, 2781-901 Oeiras, Portugal.
Department of Genetics, Forestry and Agricultural Biotechnology Institute (FABI), Genomics Research Institute (GRI), University of Pretoria, Private Bag X20, Pretoria, 0028, South Africa.
LRSV Laboratoire de Recherche en Sciences Végétales, UMR5546, Université Toulouse III, UPS, CNRS, BP 42617, Auzeville, F-31326 Castanet Tolosan, France


Auxin plays a pivotal role in various plant growth and development processes, including vascular differentiation. The modulation of auxin responsiveness through the auxin perception and signaling machinery is believed to be a major regulatory mechanism controlling cambium activity and wood formation. To gain more insights into the roles of key Aux/IAA gene regulators of the auxin response in these processes, we identified and characterized members of the Aux/IAA family in the genome of Eucalyptus grandis, a tree of worldwide economic importance. We found that the gene family in Eucalyptus is slightly smaller than that in Populus and Arabidopsis, but all phylogenetic groups are represented. High-throughput expression profiling of different organs and tissues highlighted several Aux/IAA genes expressed in vascular cambium and/or developing xylem, some showing differential expression in response to developmental (juvenile vs. mature) and/or to environmental (tension stress) cues. Based on the expression profiles, we selected a promising candidate gene, EgrIAA4, for functional characterization. We showed that EgrIAA4 protein is localized in the nucleus and functions as an auxin-responsive repressor. Overexpressing a stabilized version of EgrIAA4 in Arabidopsis dramatically impeded plant growth and fertility and induced auxin-insensitive phenotypes such as inhibition of primary root elongation, lateral root emergence and agravitropism. Interestingly, the lignified secondary walls of the interfascicular fibers appeared very late, whereas those of the xylary fibers were virtually undetectable, suggesting that EgrIAA4 may play crucial roles in fiber development and secondary cell wall deposition.


Aux/IAA; Auxin; Eucalyptus; Gene expression; Secondary cell walls; Wood formation

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