Phenolic Phytoalexins in Rice: Biological Functions and Biosynthesis

Abstract

Phytoalexins are inducible secondary metabolites possessing antimicrobial activity against phytopathogens. Rice produces a wide array of phytoalexins in response to pathogen attacks and environmental stresses. With few exceptions, most phytoalexins identified in rice are diterpenoid compounds. Until very recently, flavonoid sakuranetin was the only known phenolic phytoalexin in rice. However, recent studies have shown that phenylamides are involved in defense against pathogen attacks in rice. Phenylamides are amine-conjugated phenolic acids that are induced by pathogen infections and abiotic stresses including ultra violet (UV) radiation in rice. Stress-induced phenylamides, such as N-trans-cinnamoyltryptamine, N-p-coumaroylserotonin and N-cinnamoyltyramine, have been reported to possess antimicrobial activities against rice bacterial and fungal pathogens, an indication of their direct inhibitory roles against invading pathogens. This finding suggests that phenylamides act as phytoalexins in rice and belong to phenolic phytoalexins along with sakuranetin. Phenylamides also have been implicated in cell wall reinforcement for disease resistance and allelopathy of rice. Synthesis of phenolic phytoalexins is stimulated by phytopathogen attacks and abiotic challenges including UV radiation. Accumulating evidence has demonstrated that biosynthetic pathways including the shikimate, phenylpropanoid and arylmonoamine pathways are coordinately activated for phenolic phytoalexin synthesis, and related genes are induced by biotic and abiotic stresses in rice.

Involvement of Secondary Metabolites in Response to Drought Stress of Rice (Oryza sativa L.)

“…In the shikimate pathway, a biosynthetic pathway for aromatic L-amino acid (AAs), one of the common secondary metabolic precursors is activated early in stress-induced plants [39][40][41][42]. Many phenolic compound synthesis-related genes in the shikimate pathway are also induced immediately by stresses [42].…”

“…Many phenolic compound synthesis-related genes in the shikimate pathway are also induced immediately by stresses [42]. The expression of PAL genes (OsPALs) was proved prior to the accumulation of sakuranetin and phenylamide phytoalexins in UV-irradiated rice leaves [39,42]. The in vivo biosynthesis of kaempferol and quercetin glucosides was decided by three functional genes, UGT706C1, UGT706D1 and UGT707A3 [43].…”

From Chaos to Harmony: Responses and Signaling upon Microbial Pattern Recognition

“…In rice, chitin elicits accumulation of terpenoids, the major phytoalexins in monocots (136). Phenolic compounds, such as phenylamides, are another type of phytoalexins that accumulate in response to MAMP treatment and mainly participate in cell wall reinforcement upon pathogen attacks in rice(24). With the advancement of mass spectrometry–based metabolomics and analytical chemistry, involvement of various types of phytoalexins in PTI will likely be elucidated.…”

Combining effects of ozone and Xanthomonas oryzae pv. oryzae on antioxidants and phytoalexins in rice (Oryza sativa L.)

“…The results clearly shows the combining effects from two stresses which caused more phytoalexins production particularly sakuranetin. Basically, sakuranetin was one of antioxidant in the group of phenolic phytoalexin (Cho and Lee, 2015). The substances in this group could perform as an antioxidant against ROS (Sakihama et al, 2002).…”

“…Salicylic acid, jasmonic acid and ethylene are plant hormones that have essential roles during systemic defense signaling (Glazebrook, 2005;Robert-Seilaniantz et al, 2011). In addition, plants active defense mechanisms are generated by phytoalexins, which were antimicrobial substances of low molecular weight, promptly produced after plants were exposed to pathogen or stress (Cho and Lee, 2015;Jeandet et al, 2013;Ahuja et al, 2012). The ozone and Xanthomonas oryzae pv.…”