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Title: COMPARATIVE ANALYSIS OF EXPRESSED SEQUENCE TAGS FROM COLD ACCLIMATED AND NON-ACCLIMATED LEAVES OF RHODODENDRON CATAWBIENSE MICHX

Author
item WEI, HUI - IOWA STATE UNIV
item DHANARAJ, ANIK - IOWA STATE UNIV
item Rowland, Lisa
item FU, YAN - IOWA STATE UNIV
item KREBS, STEPHEN - HOLDEN ARBORETUM, OH
item ARORA, RAJEEV - IOWA STATE UNIV

Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/26/2004
Publication Date: 6/1/2005
Citation: Wei, H., Dhanaraj, A.L., Rowland, L.J., Fu, Y., Krebs, S., Arora, R. 2005. Comparative analysis of expressed sequence tags from cold acclimated and non-acclimated leaves of rhododendron catawbiense michx. Planta. 221:406-416.

Interpretive Summary: Interpretive Summary Cold tolerance is a limiting factor in growing related species of blueberry and rhododendron. Therefore, we have been using rhododendron, a broad-leaf, woody evergreen species, as a system for studying cold hardiness in related woody plants because there are rhododendron species that are extremely cold hardy and others that are more cold sensitive. Here, we have used a genomic approach to identify genes potentially involved in cold acclimation in rhododendron. We prepared two collections of genes, called libraries, that represent genes that are expressed in leaves in midwinter (when plants are their cold hardiest) and genes that are expressed in the spring (when plants are least cold hardy). About 450 genes were picked from each library, sequenced, and studied to compare the types of genes expressed under the two conditions. In this way, several new genes were identified that may play a role in development of cold hardiness. Scientists will benefit from this work because these genes are now available to test their involvement in cold tolerance directly. Additionally, the ~900 gene sequences represent the first database of its kind (called an expressed sequence tag or EST database) for rhododendron available to scientists for use in gene isolation, gene expression studies, and marker development.

Technical Abstract: Technical Summary An expressed sequence tag (EST) analysis approach was undertaken to identify major genes involved in cold acclimation of Rhododendron, a broad-leaf, woody evergreen species. Two cDNA libraries were constructed, one from winter-collected (cold acclimated, CA; leaf freezing tolerance -53C) leaves, and the other from summer-collected (non-acclimated, NA; leaf freezing tolerance -7C) leaves of field-grown Rhododendron catawbiense plants. A total of 862 5'-end high-quality ESTs were generated by sequencing cDNA clones from the two libraries (423 from CA and 439 from NA library). Only about 6.3% of assembled unique transcripts were shared between the libraries, suggesting remarkable differences in gene expression between CA and NA leaves. Analysis of the relative frequency at which specific cDNAs were picked from each library indicated that four genes or gene families were highly abundant in the CA library including early light-induced proteins (ELIP), dehydrins / late embryogenesis abundant proteins (LEA), cytochrome P450, and beta-amylase. Similarly, seven genes or gene families were highly abundant in the NA library and included chlorophyll a/b-binding protein, NADH dehydrogenase subunit I, plastidic aldolase, and serine:glyoxylate aminotransferase among others. Northern blot analyses for seven selected abundant genes confirmed their preferential expression in either CA or NA leaf tissues. Our results suggest that osmotic regulation, desiccation tolerance, photoinhibition tolerance, and photosynthesis adjustment are some of the key components of cold adaptation in Rhododendron.