Abstract The basal levels of salicylic acid (SA) vary dramatically among plant species. In the shoot, for example, rice contains almost 100 times higher SA levels than Arabidopsis. Despite its high basal levels, neither the biosynthetic pathway nor the biological functions of SA are well understood in rice. Combining with metabolites analysis, physiological, and genetic approaches, we found that the synthesis of basal SA in rice shoot is dependent on OsAIM1, which encodes a beta-oxidation enzyme in the phenylalanine ammonia-lyase (PAL) pathway.
Abstract Salicylic acid (SA) plays a pivotal role in plant response to biotic and abiotic stress. Several core SA signaling regulators and key proteins in SA biosynthesis have been well charactered. However, much remains unknown about the origin, evolution, and early diversification of core elements in plant SA signaling and biosynthesis. Here, we identified ten core protein families in SA signaling and biosynthesis across green plant lineages. We found that key SA signaling receptors, the nonexpresser of pathogenesis-related proteins (NPRs), originated in the most recent common ancestor (MRCA) of land plants and formed divergent groups in the ancestor of seed plants.