Submitted to: Bryologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/20/1999
Publication Date: N/A
Interpretive Summary: In order to increase our understanding of drought tolerance we are investigating the ability of a native species, Tortula ruralis, to survive the severest of drought conditions, vegetative desiccation. In our previous work we have established that one of the means by which this plant can maintain cellular integrity is its ability to store gene transcripts during gdrying. In this report we investigate the structural nature of Tortula transcripts in order to determine which aspects of their sequence enables their storage. We have identified several sequences within Tortula transcripts that appear to be conserved. The conservation of these sequences points to their importance and functional nature. This is the first time such sequences have been identified for this class of plants and thus this study provides a foundation upon which further studies can be based. It is our hope that by manipulating transcript structure we can determine which sequences render the transcripts candidates for storage during drought conditions.
Technical Abstract: Tortula ruralis is a desiccation-tolerant bryophyte with a novel post- transcriptional gene response to drying and rehydration. To understand the basis of mRNA stability and selection, 149 T. ruralis cDNAs were analyzed by sequence comparison for cis-acting elements associated with the formation of mRNA 3'-ends. The cDNAs analyzed were 146 expressed sequence tags isolated from dried moss, a calmodulin-like domain protein kinase, th rehydrins Tr155 and Tr288. The majority of cDNAs contained within the 3' untranslated region (3'UTR) a consensus AAUAAA poly (A) signal and a highly conserved far-upstream element (FUE) that was similar to the plant consensus GU-rich sequence. The T. ruralis FUE consensus sequence is (A/U)UUUUGUU(G/U) which we have designated the UUG-core motif. We have characterized five classes of cDNAs based upon the modular architecture of the poly (A) signal motif. Each cDNA class, with the exception of class V, contained the UUG-core motif. Class I contained the conserved poly (A) signal sequence 0 30 nucleotides from the poly (A) site. Class II contained a consensus hexanucleotide 0-30 nucleotides from the poly (A) site. Class III contained an exact copy of a related poly (A) signal (AAUGAA) more than 30 nucleotides from the poly (A) site. Class IV contained a consensus hexanucleotide more than 30 nucleotides from the poly (A) site. Class V contained no known poly (A) signal. Putative poly (A) signals are arrayed within the 3'UTR of T. ruralis cDNAs as predicted from the angiosperm model systems. This is the first description of the molecular architecture of poly (A) signals within bryophyte cDNAs.