Analysis of mRNA stabilities during pollen development and in BY2 cells

RNA stability is important in post-transcriptional gene expression. However , its role during plant male gametophyte development has not been studied i n detail, probably because of technical difficulties and because earlier wo rk suggested that, in general, mRNAs expressed during late pollen developme nt would be stable. We determined mRNA stabilities of 12 pollen-expressed g enes. We measured pollen mRNA decay during in planta development and in vit ro maturation after transcriptional inhibition with ActinomycinD (ActD). Be cause five of these genes were also expressed in somatic cells we also meas ured RNA decay in BY2 cells after transcriptional inhibition with ActD. Ten of the mRNAs were highly stable during pollen development (t(1/2)>30h), in cluding all seven pollen-specific mRNAs. However, two mRNAs showed a logari thmic decrease as pollen development proceeded, both in planta and in vitro . In fact, for one of these two, GUT8-2b, the mRNA level decreased signific antly within 3h. Our results show that many pollen-expressed mRNAs are inde ed long-lived but that at least some mRNAs undergo decay during pollen matu ration. Thus, there is no overall cytoplasmic condition in pollen that stab ilizes mRNAs and specific mRNA turnover mechanisms must exist. We detected reciprocal mRNA stabilities with two genes that are expressed in both BY2 c ells and pollen. GUT15 mRNA, known to be unstable (t(1/2)<3h) in BY2 cells, was highly stable in pollen. In contrast, GRP2 mRNA decayed in pollen but was highly stable in BY2 cells. Therefore, we conclude that mRNA stability can be tissue-specific.