Plant Molecular Biology 39: 823–833, 1999.
© 1999 Kluwer Academic Publishers. Printed in the Netherlands.
Degradation of oat mRNAs during seed development
Russell R. Johnson
, Marta E. Chaverra
, Harwood J. Cranston
, Tzili Pleban
William E. Dyer
Department of Biology, Colby College, Waterville, ME 04901-8857, USA;
Department of Plant Sciences,
Montana State University, Bozeman, MT 59717-0312, USA (
author for correspondence)
Received 9 July 1998; accepted in revised form 10 November 1998
Key words: avenin, oats, protein Z, puroindoline, RNA degradation
The genes AV1, AV10,andZ1 encode proteins that accumulate during oat seed development. In developing
endosperm of Avena sativa (cultivated oat), AV1, AV10 and Z1 mRNAs reach maximal levels midway through
seed development but fall to very low levels in mature seeds. Similarly, mRNAs for these proteins peak during en-
dosperm developmentof Avena fatua (wild oat) and are later degraded. However, during late maturation of A. fatua
seeds, populations of mRNA fragments shorter than the intact transcripts accumulate as the full-length transcripts
decline in abundance. The smaller RNA molecules, which are apparently long-lived decay intermediates, are
derivedrandomlyfromtheentiretranscriptsand are most likely not generatedbycleavageat preciselydeﬁnedsites.
Other A. fatua endosperm mRNAs that are degraded during late seed development, such as those for ADP glucose
pyrophosphorylase and starch synthase, do not produce detectable decay intermediates. Decay intermediates of
AV1 and Z1 mRNAs persist at high levels during late seed development of two other undomesticated oat species,
Avena strigosa and Avena barbata. The persistence of decay intermediates for these endosperm mRNAs in wild
grass species may represent a model system for studying RNA decay process in plant tissues.
Control of mRNA stability plays a critical role in
the overall regulation of gene expression, in coopera-
tion with transcriptional and translational controls .
Degradation of most mRNA transcripts is tightly reg-
ulated and is often mediated by interactions between
speciﬁc nucleotide sequences and factors that bind to
these elements [3, 38]. In plants, most mRNAs have
half-lives on the order of several hours and are be-
lieved to be inherently stable unless they are actively
destabilized [55, 56].
Several recent studies have focused on the mech-
anisms that control mRNA stability in plants. These
efforts have identiﬁed speciﬁc sequences that target
short-lived mRNAs for rapid degradation [33, 38, 39].
The nucleotide sequence data reported will appear in the
EMBL, GenBank and DDBJ Nucleotide Sequence Databases un-
der the accession numbers AF118559 (AV1), AF118560 (Z1), and
Stability-conferring motifs have been characterized in
several animal systems [28, 29] but verylittle is known
about speciﬁc sequences or factors that may confer
high stability to plant mRNAs. The poly(A) tail and
cap have been shown to have stabilizing effects on
some plant transcripts  but so far no internal plant
mRNA motifs have been identiﬁed that protect against
degradation.In almost all cases, once mRNA degrada-
tion is initiated, full-length transcripts are very rapidly
converted into fragments too small to be detected on
RNA blots, indicating that mRNA decay intermediates
are extremely transient .
During seed development a number of mRNAs
accumulate and then decline in developmentally reg-
ulated patterns, including those for important seed
proteins like storage proteins , enzymes for starch
biosynthesis , and late embryogenesis-abundant
(LEA) proteins . mRNAs for certain storage pro-
teins such as prolamines , protein Z , and
puroindolines  are expressed speciﬁcally in cereal