In silico Analysis of Polyamine Rich Transgenic Tomato Fruit Transcriptome for Salicylic Acid Biosynthesis

Abstract

EFFECT of higher levels of polyamines (PAs), spermidine (SPD) and spermine (SPM), were evaluated on the salicylic acid biosynthesis genes. It has been previously reported that higher steady state levels of a pathogenesis protein pR1b1, a salicylic acid (SA) regulated protein, are present in tomato fruits with higher levels of anabolic biogenic amines, spermidine (SPD) and spermine (SPM) resulting from the expression of yeast S-adenosylmethionine decarboxylase (SAMDC), under a fruit specific E8 promoter in ripening tomato fruit. Based on this observation, we hypothesized that high SPD/SPM fruit would enhance the expression of SA- biosynthesis genes leading to enhanced SA production. In plants, SA is synthesized either through phenylalanine ammonia-lyase (PAL) or isochorismate synthase (ICS) pathway. We identified ten putative genes for the SA biosynthesis pathways in tomato and determined the relative abundance of their transcript based on RNAseq transcriptomic analyses of mature green and turning stage tomato fruits from WT and two isogenic independent SAMDC-transgenic homozygous lines with higher levels of SPD/SPM in ripening fruits. We show that at MG stage the transgenic fruits exhibited higher steady state levels of transcripts of CS, PAL1-7, ICS, IPL/PRXR1, CS, and PAL 4-10, but lower levels for CM1, CM2, EPS1, and PBS3-2. At the turning stage of tomato fruit ripening the steady state levels of only CS and PBS3-2 were upregulated whereas the transcript levels of CM1, CM2, PaL1-4AAO, PBS3-1and EPS1 were down regulated. Taken together these results suggest that SPD/SPM play role in the SA biosynthesis and higher levels of various genes especially in in PAL pathway likely increased the SA levels in the transgenic fruits.