Overexpression of PDH45 or SUV3 helicases in rice leads to delayed leaf senescence-associated events

Senescence is a very complex process characterized by a highly regulated series of degenerative events which include changes in cell structure, metabolism and gene expression. In animals, one of the indicators of senescence is telomere shortening. In plants, this aspect is more puzzling because telomere shortening is not always correlated with senescence. In some cases, there were no differences in telomere length during plant developmental stages while in other cases both shortening and lengthening have been observed. Several genes involved in telomere homeostasis have been identified in plants, including some helicases. In the present study, the salinity stress-tolerant transgenic IR64 rice plants overexpressing the PDH45 (Pea DNA Helicase 45) or SUV3 (Suppressor of Var1-3) genes were used to test their performance during natural senescence at flowering (S2) and seed maturation (S4) developmental stages. Our results reveal that both PDH45 and SUV3 transgenic rice lines present decreased levels of necrosis/apoptosis as compared to wild type plants. Additionally, in these plants, some senescence-associated genes (SAGs) were downregulated at S2 and S4 stages, while genes involved in the maintenance of genome stability and DNA repair were upregulated. More interestingly, the telomeres were up to 3.8-fold longer in the SUV3 overexpressing lines as compared to wild type plants. This was associated with an increase (2.5-fold) in telomerase (OsTERT) transcript level. This is an interesting result reporting a possible involvement of SUV3 in telomere homeostasis in plants.