NnSR1, a class III ribonuclease induced under P stress in Nicotiana, is localized in ER compartments

ROJAS HERNAN JAVIER; GOLDRAIJ ARIEL; GUSTAVO C. MACINTOSHC; BRICE FLOYD; STEPHANIE C. MORRISS; DIANE BASSHAM

Rosario

Congreso; L Reunión Anual de la Sociedad Argentina de Investigaciones en Bioquímica y Biología Molecular (SAIB); 2014

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

Ribonucleases (RNases) T2 are endonucleolytic enzymes that catalyze the cleavage of single-strand RNA, producing mononucleotides with a terminal 3´ phosphate (Pi). In plants, RNases T2 are grouped in three classes: Class I and class II S-like-RNases are induced in a variety of stress scenarios, including Pi starvation. The induction of these RNases contributes to Pi mobilization from nucleic acid sources. Class III includes S-RNases, involved in the selfincompatibility reaction and non S-RNases, whose function is unknown. Here, we compare the expression of several RNases of Nicotiana alata under Pi deprivation. We confirmed that class III NnSR1 (Nicotiana non S-RNaseI) andclass I NE are, thus far, the only RNases induced for Pi mobilization in this plant. To test its subcellular localization, NnSR1 was transiently expressed in Arabidopsis protoplasts and Nicotiana leaves as a fusion protein, conjugated to a fluorescent protein. In both cases, NnSR1 colocalized with a fluorescent ER marker. A subcellular fractionation of roots exposed to Pi deprivation showed that the induced native NnSR1 was predominantly associated with ER membranes. NnSR1 appeared to be expressed slightly before the extracellular NE, suggesting that intracellular RNA may be the first source of Pi used by the cell under Pi stress.