Auxin-induced gene expression in loblolly pine (Pinus taeda L.)

We used microarrays to identify auxin-induced genes from loblolly pine. From about 200 putatively differentially expressed ESTs, nine were further studied. Induction levels from the microarray analysis were verified by northern blotting. We found good correspondence for seven of the nine clones. Sequence analysis of the nine clones indicated that they encode proteins from different functional groups and pathways. Three clones encode methionine synthase, serine hydroxymethyl transferase and caffeoyl-CoA-methyltransferase. These three enzymes are involved in the lignin biosynthesis, supporting the role of auxin in lignification. Two clones (5ca7 and 9228) show homology to light-induced genes, indicating interaction between auxin and light signaling. Three clones encode proteins implicated in root developmental processes. One (6ca1) shows homology to a subtilisin protease (AIR3) and another (7cg8) to a proline rich protein (AIR1) from Arabidopsis. Both Arabidopsis genes are induced by auxin during lateral root formation. The third clone (5ng4) showed homology to the MtN21 nodulin from Medicago induced after Rhizobium inoculation.; We used northern blotting to characterize the expression in mature and juvenile shoots. In addition to the nine clones identified in this study, we screened for differential expression five pine genes (LPEA1-5) homologous to the Aux/IAA gene family. We found significant expression reduction in mature shoots only for 5ng4. This p&barbelow;ine a&barbelow;uxin i&barbelow;nduced n&barbelow;odulin1 (PAIN1) was further characterized. PAIN1 predicted protein sequence indicates that this is a membrane protein, with high sequence conservation in Arabidopsis, Oryza and Medicago. A gene family of 38 members was identified in the Arabidopsis genome. This redundancy is probably associated with functional divergence or the need for expression specificity of the family members. Differential expression of PAIN1 was also found in xylem forming top and bottom wood. The localization of PAIN1:GFP protein at the periphery of tobacco cells is consistent with the transmembrane sequence predictions. The occurrence of the fusion protein in punctate structures possibly part of the Golgi apparatus is consistent with the predictions that the protein is targeted to the secretory pathway.