NnSR1, aclass III non-S-RNase constitutively expressed in styles, is induced in roots and stems under phosphate deficiency in Nicotiana alata

ROJAS HERNAN JAVIER; ROLDAN JUAN ALFREDO; GOLDRAIJ ARIEL

ANNALS OF BOTANY

OXFORD UNIV PRESS

Lugar: Oxford; Año: 2013 vol. 112 p. 1351 - 1360

0305-7364

? Background and Aims Non-S-ribonucleases (non-S-RNases) are class III T2 RNases constitutively expressed instyles of species with S-RNase-based self-incompatibility. So far, no function has been attributed to theseRNases. The aim of this work is to examine if NnSR1, a non-S-RNase from Nicotiana alata, is induced under conditionsof phosphate (Pi) deprivation. The hypothesis is that under Pi-limited conditions, non-S-RNase functionsmayresemble the role of S-like RNases. To date, the only RNases reported to be induced by Pi deficiency are class I andclass II S-like RNases, which are phylogenetically different from the class III clade of RNases.? Methods Gene and protein expression of NnSR1were assayed in plants grown hydroponically with and without Pi,by combining RT-PCR, immunoblot and enzymatic activity approaches.? Key Results NnSR1 transcripts were detected in roots 7 d after Pi deprivation and remained stable for several days.Transcript expression was correlated based on Pi availability in the culture medium. Antiserum against a peptidebased on a hypervariable domain of NnSR1 recognized NnSR1 in roots and stems but not leaves exposed to Pi shortage.NnSR1was not detected in culture medium andwas pelleted with the microsomal fraction, suggesting that itwasmembrane-associated or included in large compartments. The anti-NnSR1 inhibited selectively the enzymatic activityof a 31-kDa RNase indicating that NnSR1 was induced in an enzymatically active form.?Conclusions The induction of NnSR1 indicates that there is a general recruitment of all classes of T2 RNases inresponse to Pi shortage. NnSR1 appears to have regained ancestral functions of class III RNases related to strategiesto cope with Pi limitation and also possibly with other environmental challenges. This constitutes the first report for aspecific function of class III RNases other than S-RNases.