Inferring Roles in Defense from Metabolic Allocation of Rice Diterpenoids

Abstract

Among their responses to microbial infection, plants deploy an arsenal of natural antibiotic products. Historically these have been identified on the basis of their antibiotic activity in vitro, which leaves open the question of their relevance to defense in planta. The vast majority of such natural products from the important crop plant rice () are diterpenoids whose biosynthesis proceeds via either - or-copalyl diphosphate (CPP) intermediates, which were isolated on the basis of their antibiotic activity against the fungal blast pathogen However, rice plants in which the gene for the-CPP synthase is knocked out do not exhibit increased susceptibility to Here, we show that knocking out or knocking down actually decreases susceptibility to the bacterial leaf blight pathogen By contrast, genetic manipulation of the gene for the -CPP synthase alters susceptibility to both and Despite the secretion of diterpenoids dependent on or from roots, neither knockout exhibited significant changes in the composition of their rhizosphere bacterial communities. Nevertheless, rice plants allocate substantial metabolic resources toward - as well as-CPP derived diterpenoids upon infection/induction. Further investigation revealed that plays a role in fungal non-host disease resistance. Thus, examination of metabolic allocation provides important clues into physiological function.

The foxtail millet (Setaria italica) terpene synthase gene family

“…While the molecular mechanisms underlying environmental resilience in millets have remained largely unknown, related monocot crops, especially rice (Oryza sativa) and maize (Zea mays), deploy species-specific mixtures of terpenoid metabolites as core modulators of both biotic and abiotic stress defenses (Schmelz et al, 2014;Murphy and Zerbe, 2020). Rice accumulates distinct groups of stress-inducible diterpenoid phytoalexins with potent antimicrobial efficacy against major rice pathogens such as rice blast (Magnaporthe oryza) (Xu et al, 2012;Bagnaresi et al, 2012;Han et al, 2015;Lu et al, 2018). Among these bioactive diterpenoids, momilactones further demonstrate allelopathic functions (Kato-Noguchi and Peters, 2013;Toyomasu et al, 2014).…”

Functional Characterization of Two Class II Diterpene Synthases Indicates Additional Specialized Diterpenoid Pathways in Maize (Zea mays)

“…Two of the most agroeconomically important grain crops, maize ( Zea mays ) and rice ( Oryza sativa ), deploy distinct networks of diterpenoids to mediate the plant response to biotic and abiotic stress (for review, see Peters, 2006 ; Schmelz et al, 2014 ). Rice produces a complex suite of diterpenoid phytoalexins, including momilactones, oryzalexins, and phytocassanes, that serve as major components of disease resistance and exhibit allelopathic properties to suppress the growth of competing weeds ( Peters, 2006 ; Kato-Noguchi and Peters, 2013 ; Toyomasu et al, 2014 ; Lu et al, 2018 ). Similarly, maize produces related yet distinct arsenals of bioactive diterpenoids that, to current knowledge, include the kauralexin and dolabralexin groups with demonstrated and predicted functions in maize chemical defense (Figure 1 ; Schmelz et al, 2011 ; Vaughan et al, 2015 ; Christensen et al, 2018 ; Mafu et al, 2018 ).…”

Divalent nutrient cations: friend and foe during zinc stress in rice

“…The growth hormone GA and defense-related phytoalexins and phytoanticipins are derived from the diterpenoid pathway, so the coordinated control of this pathway is needed for the efficient allocation of metabolic resources to growth or defense (Lu et al ., 2018). The pathway branches when GGPP is converted into one of the two stereoisomers ent -CPP and syn -CPP, with GA derived from the former and each branch also giving rise to different phytoalexins/phytoanticipins ( Figure 6B).…”

“…When exposed to microbial infection, rice plants allocate metabolic resources to the synthesis of diterpenoid phytoalexins, including momilactones A and B, oryzalexins A-F, oryzalexin S and phytocassanes A-E, by inducing the corresponding genes (Lu et al ., 2018). For example, Shimizu et al .…”

“…Momilactones and phytocassanes also accumulated in rice leaves following infection with the bacterial leaf blight pathogen,Xanthomonas oryzae (Klein et al ., 2015). However, given that the knockdown of OsCPS4 and the overexpression ofOsCPS2 reduces susceptibility to X. oryzae infection, phytocassanes are likely to be the most effective phytoalexins against this pathogen (Lu et al ., 2018). OsCPS4 (or thesyn -CPP route) also confers resistance to fungal non-host disease in rice (Lu et al ., 2018).…”