<p>Auxin is an important plant growth regulator affecting many aspects of plant growth and development. Maturation is an epigenetic developmental process that affects several processes and traits of economic importance that are regulated by auxin. Among these are elongation growth, wood formation and adventitious rooting. We hypothesized that maturation blocks auxin-regulated pathways that carry out these processes. The objective of this study was to identify genes that are differentially expressed in mature and juvenile loblolly pine shoots after auxin treatment.We used microarray screening to identify auxin-induced genes from loblolly pine. From about 200 putatively differentially expressed ESTs, nine were chosen for further study. Induction levels from the microarray analysis were verified by northern blotting using the same RNA that was used in the microarray probe synthesis. We found good correspondence for seven of the nine clones. However, the induction levels of two clones were underestimated by the microarray. Sequence analysis of the nine clones indicated that they encode proteins that belong to different functional groups and pathways. Three clones encode methionine synthase (MS), serine hydroxymethyl transferase (SHM) and caffeoyl-CoA-methyltransferase (CCoAM). These three enzymes are involved in the pathway leading to production of lignin, supporting the role of auxin in the lignification process. Two other clones show homology to light-induced genes, indicating interaction between auxin and light signaling pathways. One of these clones (9228) is a repressor of plastid rRNA gene, suggesting that auxin may repress photomorphogenesis. Three clones encode proteins previously implicated in root-related developmental processes. One (6ca1) shows homology to a subtilisin protease (AIR3) and another (7cg8) to a proline rich protein (AIR1) from Arabidopsis thaliana. Both Arabidopsis genes are induced by auxin and are expressed during lateral root formation. The third clone (5ng4) showed homology to the MtN21 nodulin from Medicago truncatula that is induced after Rhizobium inoculation. Auxin may play an important role in nodule formation, possibly by triggering a lateral root developmental program that is later modified by the symbiont into nodule formation.We used northern blotting to characterize the expression patterns in mature and juvenile shoots treated with auxin. In addition to the nine clones identified in this study, we screened for differential expression five pine genes (LPEA1-5) that show homology to the Aux/IAA gene family. We found significant expression reduction in mature shoots only for 5ng4. This pine auxin induced nodulin1 (PAIN1) clone was further characterized. The full PAIN1 predicted protein sequence indicates that this is most likely a membrane protein with 10 transmembrane helices, the N- and C-termini in the cytoplasm and a pore-like region separating the two five- transmembrane domains with high sequence conservation in Arabidopsis, Oryza and Medicago. The high degree of conservation indicates essential function in plant growth and development. A large gene family of 38 members was identified in the Arabidopsis genome. The functional significance of this redundancy is most likely associated with functional divergence and/or the need for expression specificity of the different family members. PAIN1 induction is auxin-specific and is restricted to stems, hypocotyls and roots, all three competent to form lateral or adventitious roots. Differential expression of PAIN1 was also found in developing xylem forming top and bottom wood. The localization of a PAIN1:GFP fusion protein at the periphery of tobacco cells is consistent with the transmembrane sequence predictions. The occurrence of the fusion protein in punctate structures that could be part of the Golgi apparatus is consistent with the sequence predictions that the protein is targeted to the secretory pathway. Further determination of the biochemical and developmental function of the genes identified here should increase our understanding of auxin-dependent processes and how they are affected by maturation.<P>
| Identifer | oai:union.ndltd.org:NCSU/oai:NCSU:etd-20020102-091427 |
| Date | 02 January 2002 |
| Creators | Busov, Victor Borissov |
| Contributors | Barry Goldfarb, Steven L. Spiker, Ross W. Whetten, Ronald R. Sederoff |
| Publisher | NCSU |
| Source Sets | North Carolina State University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://www.lib.ncsu.edu/theses/available/etd-20020102-091427 |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to NC State University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
Page generated in 0.0111 seconds