Despite the prevailing belief that translating mRNAs are excluded from degradation, co-translational mRNA decay (CTRD), a mechanism that degrades mRNAs associated with actively translating ribosomes, has been identified in Arabidopsis, rice, and soybean as well as in yeast and humans. However, it is not known whether this decay mechanism is conserved in other plant species. Moreover, the regulation and physiological significance of this decay mechanism is also less well known. In this thesis, I describe research where I found that co-translational mRNA decay is conserved in at least 10 angiosperm species and present in many tissues as well as among various growth stages and environmental conditions. Additionally, I discovered that the co-translationally decayed mRNAs in every species consistently harbor sequence features linking to low translation activity. In terms of CTRD regulation, I have identified Arabidopsis Pelota and Hbs1 as suppressors of CTRD in vivo. Lastly, I demonstrated that Pelota and Hbs1 loss of function mutants (pel and hbs1, respectively) have lower germination rates, which might be due to embryo development defects caused by increased levels co-translational mRNA decay induced down-regulation of relevant transcripts in these mutant backgrounds. These results indicate that the level of co-translational mRNA decay needs to be tightly controlled to ensure normal physiological functions in plant species. Taken together, my study expanded the general knowledge concerning the regulation and physiological significance of CTRD in plants as well as presented the sequence features associated with the co-translationally decayed mRNAs, which provided insights into the possible triggering mechanism for this decay mechanism.