Seed priming with spermine and spermidine regulates the expression of diverse groups of abiotic stress-responsive genes during salinity stress in the seedlings of indica rice varieties

Abstract

Seed priming with polyamines (PAs) is one of the most desirable techniques to enhance stress tolerance, since it provides prolonged and potential protection to multiple stresses with minimal application cost. In the present study, the main aim was to analyze the effect of seed priming with spermine (Spm) and spermidine (Spd) in salt stressed IR-64 (salt-sensitive) and Nonabokra (salt-tolerant) seedlings with respect to the regulation of genes controlling multiple metabolic pathways governing salt tolerance. The transcriptome profiling of key genes, encoding non-enzymatic and enzymatic antioxidants (ANS, CAT, SOD, APX, GR), osmolyte (P5CS, PDH, BADH1), ABA biosynthetic enzyme (NCED3), transcription factors (TRAB1, WRKY71), LEA (Osem), ion transporter (NHX1), PA-metabolic enzymes (SAMDC, SPDS, SPMS, DAO, PAO) and content of endogenous PAs, responsible for stress tolerance were studied in the shoots and roots of both the cultivars. Our data showed that both Spm and Spd priming enhanced the expression of antioxidant genes in shoots and roots with respect to non-primed stressed seedlings; however, the expression was enhanced more with Spm priming in the salt-sensitive cultivar during stress. Priming with Spm and Spd also increased the expression of osmolyte biosynthetic genes. In addition, both the PAs significantly enhanced the expression of ABA biosynthesis gene, along with increased expression of ABA-inducible transcription factors and LEA gene in both shoots and roots; Spm application triggered better expression. Seed priming with Spd also altered the expression of ion transporter like NHX1 under stress in the shoots of both the cultivars, with better effect in IR-64. Salinization increased (Spm+Spd)/Put ratio more in the tolerant cultivar. Priming with both PAs increased (Spm+Spd) to Put ratio in the two cultivars; however, with Spm, the (Spm+Spd)/Put ratio was increased more in IR-64 together with the coordinated expression of PA biosynthesis and catabolic genes. The down regulation of RbcS expression as a result of salt stress was significantly restored in primed seedlings due to coordinated regulation of the defense pathway. The current results suggest that seed pretreatment with Spm or Spd affects several metabolic pathways to overcome salt stress, with more pronounced effect of Spm in the salt-sensitive cultivar. Spm and Spd could therefore act as nodal regulators of salt stress response by initiating a well-organized crosstalk with multiple metabolic pathways governing salt tolerance. Our observation clearly highlights the intricate interaction of PAs with different stress-related pathways.