Degradation of endosperm mRNAs during dry afterripening of cereal grains

Abstract

AbstractThe endosperm of dormant wild oat (Avena fatuaL.) grains contains a number of mRNAs, including low levels of transcripts encoding avenin (AV10), puroindoline-like (AV1) and serine proteinase inhibitor-like (Z1) proteins. During dry afterripening, a period of warm dry storage that relieves dormancy, the abundance of these intact transcripts gradually declined to undetectable levels in pooled grain samples. In contrast, the three mRNAs did not decline in grains stored for the same period at −20°C, and levels of mRNA decay products derived from these transcripts did not change during afterripening. Disappearance of the three intact mRNAs was not a general phenomenon, since abundance of more than 5000 other seed mRNAs did not change during this period. Additional experiments were conducted to test the idea that the presence of these transcripts was positively correlated with seed dormancy status. First, the rate of intactZ1mRNA decline was similar to the rate of dormancy relief during 9 months of afterripening. Second, cultivated oat (A. sativa) grains (which are not dormant at maturity) contained much lower levels of these mRNAs than did highly dormant wild oat grains. Third, levels of full-lengthAV1andZ1mRNAs remained constant in dormant grains during 6 d of imbibition. However, Northern analyses of individual grains from a partially afterripened seed lot showed that amounts of intactAV1orZ1mRNAs were highly variable in germinating and dormant grains and were not correlated with dormancy status. Even though loss of these transcripts occurred under the same environmental conditions that promote afterripening, a causal relationship between the two processes seems unlikely. The apparently specific mechanism(s) by which these mRNAs are degraded in endosperm tissue may represent a novel post-transcriptional process for regulating levels of certain transcripts in dry grains.