A distinctive class of spermidine synthase is involved in chilling response in rice

A cDNA for a putative 42 kD spermidine synthase (OsSPDS2) was cloned from rice. The deduced OsSPDS2 sequence showed highest similarity with Arabidopsis AtSPDS3. Phylogenetic analysis revealed that OsSPDS2 and AtSPDS3 form a distinctive subclass in the spermidine synthase family in plants. OsSPDS2 mRNA accumulated in roots during long term exposure to chilling temperature (12°C). In contrast, no such induction of the paralogous OsSPDS1 was observed during the chilling treatment. ABA treatment up-regulated OsSPDS2, whereas salt stress did not change OsSPDS2 levels significantly. Data suggested a distinct function of OsSPDS2 in chilling response in rice.