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Title: Spatio-temporal expression patterns of Arabidopsis thaliana and Medicago truncatula defensin-like genes

item TESFAYE, MESFIN - University Of Minnesota
item SILVERSTEIN, KEVIN A - University Of Minnesota
item NALLU, SUMITHA - University Of Minnesota
item WANG, LIN - University Of Minnesota
item BOTANGA, CHRISTOPHER - University Of Minnesota
item GOMEZ, S. KAREN - Boyce Thompson Institute
item HARRISON, MARIA - Boyce Thompson Institute
item Samac, Deborah - Debby
item GLAZEBROOK, JANE - University Of Minnesota
item KATAGIRI, FUMI - University Of Minnesota
item GUTIERREZ-MARCOS, JOSE - University Of Warwick
item VANDENBOSCH, KATHRYN - University Of Minnesota

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/8/2013
Publication Date: 3/18/2013
Citation: Tesfaye, M., Silverstein, K.T., Nallu, S., Wang, L., Botanga, C.J., Gomez, S., Harrison, M., Samac, D.A., Glazebrook, J., Katagiri, F., Gutierrez-Marcos, J.F., VandenBosch, K.A. 2013. Spatio-temporal expression patterns of Arabidopsis thaliana and Medicago truncatula defensin-like genes. PLoS One. 8(3):e58992.

Interpretive Summary: Plants produce a wide variety of proteins as part of their arsenal of defenses against disease-causing microorganisms. One group of proteins, called defensins, are similar to antimicrobial compounds produced by animals as part of an ancient immune response. A scan of the genes sequences in two model plant species, Medicago and Arabidopsis, identified a large number of novel genes with similarity to defensins. To determine the role of these defensin-like genes, a survey was done to determine the location and timing of expression of each defensin-like gene during plant growth and with challenge by pathogenic microorganisms. Defensin-like genes appear to play very different roles in the two plant species. Surprisingly, only a small set are pathogen responsive in the two plant species. In Arabidopsis, most defensin-like genes are active in developing flower buds and in roots. Approximately one-third have unique and specific patterns of activity and a small group are active in all tissues at all times. In Medicago, only a small number are active in flowers or seeds with the majority of defensin-like genes active in roots interacting with beneficial bacteria and fungi that are critical for the plant to obtain nitrogen and phosphorus, key elements in plant nutrition. Some of the defensin-like genes may have a role in regulating development of these microorganisms. Several defensin-like genes were identified that are active along with other disease defense genes and will be tested further for their potential to enhance disease resistance. This work enhanced understanding of a new group of plant proteins that have potential for increasing plant productivity through nutrient acquisition and in defense against pathogenic microorganisms.

Technical Abstract: Plant genomes typically contain several hundred defensin-like (DEFL) genes that encode short proteins resembling defensins, which are antimicrobial polypeptides. Little is known about the expression patterns of DEFL genes because most were recently discovered and many are not well represented on standard microarray chips. To make a comparative analysis of DEFL gene expression in two model species, we designed a custom Affymetrix chip for transcript profiling of nearly all DEFL genes from Arabidopsis thaliana and Medicago truncatula, as well as additional genes for data normalization. We examined three normalization algorithms and found that the Stable-Based Quantile (SBQ) approach is the preferred normalization approach for the custom chip. The DEFL gene chip analysis provided evidence for the transcription of many of the recently identified DEFL genes that previously lacked gene expression data. DEFL gene expression patterns appear highly condition-specific and differ strikingly between Arabidopsis and Medicago. DEFL gene expression in Arabidopsis was most pronounced in inflorescences, whereas DEFL genes in Medicago were expressed primarily in nitrogen-fixing nodules. Both species contain a subset of DEFL genes specifically expressed in seeds. A few DEFL genes and classical defensins were significantly induced in pathogen-infected tissues of Arabidopsis and Medicago. Using plant and bacterial mutants with defects in defense signaling and co-expression analysis with three marker genes for early defense signaling and jasmonic acid-mediated host response, we were able to identify a few DEFL genes that may be associated with putative defense responses.