Expressed sequence tag analysis in Cycas, the most primitive living seed plant.
BACKGROUND
Cycads are ancient seed plants (living fossils) with origins in the Paleozoic. Cycads are sometimes considered a 'missing link' as they exhibit characteristics intermediate between vascular non-seed plants and the more derived seed plants. Cycads have also been implicated as the source of 'Guam's dementia', possibly due to the production of S(+)-beta-methyl-alpha, beta-diaminopropionic acid (BMAA), which is an agonist of animal glutamate receptors.


RESULTS
A total of 4,200 expressed sequence tags (ESTs) were created from Cycas rumphii and clustered into 2,458 contigs, of which 1,764 had low-stringency BLAST similarity to other plant genes. Among those cycad contigs with similarity to plant genes, 1,718 cycad 'hits' are to angiosperms, 1,310 match genes in gymnosperms and 734 match lower (non-seed) plants. Forty-six contigs were found that matched only genes in lower plants and gymnosperms. Upon obtaining the complete sequence from the clones of 37/46 contigs, 14 still matched only gymnosperms. Among those cycad contigs common to higher plants, ESTs were discovered that correspond to those involved in development and signaling in present-day flowering plants. We purified a cycad EST for a glutamate receptor (GLR)-like gene, as well as ESTs potentially involved in the synthesis of the GLR agonist BMAA.


CONCLUSIONS
Analysis of cycad ESTs has uncovered conserved and potentially novel genes. Furthermore, the presence of a glutamate receptor agonist, as well as a glutamate receptor-like gene in cycads, supports the hypothesis that such neuroactive plant products are not merely herbivore deterrents but may also serve a role in plant signaling.
Brenner
Eric D
ED
The New York Botanical Garden, 200th Street and Kazimiroff, Bronx, NY 10458-5126, USA. ebrenner@nybg.org
Stevenson
Dennis W
DW
McCombie
Richard W
RW
Katari
Manpreet S
MS
Rudd
Stephen A
SA
Mayer
Klaus F X
KF
Palenchar
Peter M
PM
Runko
Suzan J
SJ
Twigg
Richard W
RW
Dai
Guangwei
G
Martienssen
Rob A
RA
Benfey
Phillip N
PN
Coruzzi
Gloria M
GM
D000599:Amino Acids, Diamino / Q000096:biosynthesis; D000087522:Cyanobacteria Toxins; D032462:Cycadopsida / Q000235:genetics; D029784:Cycas / Q000235:genetics* / Q000378:metabolism; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D020224:Expressed Sequence Tags; D015723:Gene Library; D017343:Genes, Plant / Q000235:genetics; D017422:Sequence Analysis, DNA; D015398:Signal Transduction / Q000235:genetics
D000599:Amino Acids, Diamino; D000087522:Cyanobacteria Toxins; D018076:DNA, Complementary; C001824:beta-N-methylamino-L-alanine