Compromised disease resistance in saponin-deficient plants

Gene Clusters for Secondary Metabolic Pathways: An Emerging Theme in Plant Biology

“…These clusters are diverse in organization and function and all appear to have evolved independently (Field and Osbourn, 2008;Frey et al, 2009;Osbourn and Field, 2009;Swaminathan et al, 2009). The four clusters from cereals are all required for the synthesis of preformed or stress-induced compounds implicated in plant defense (Papadopoulou et al, 1999;Gierl and Frey, 2001;Wilderman et al, 2004;Shimura et al, 2007). The function of the Arabidopsis thalianol cluster is not known, but the high level of conservation of this cluster across different Arabidopsis accessions suggests that it is also like to have an important function in ecological interactions (Field and Osbourn, 2008).…”

“…Unlike operons, the genes within these clusters are transcribed separately. The five plant clusters are for the synthesis of cyclic hydroxamic acids in maize (Frey et al, 1997(Frey et al, , 2003(Frey et al, , 2009von Rad et al, 2001;Jonczyk et al, 2008), triterpenes in oat (Avena sativa) and Arabidopsis (the avenacin and thalianol clusters, respectively; Papadopoulou et al, 1999;Haralampidis et al, 2001;Qi et al, 2004Qi et al, , 2006Field and Osbourn, 2008;Mylona et al, 2008;Mugford et al, 2009), and diterpenes in rice (Oryza sativa; the momilactone and phytocassane clusters; Sakamoto et al, 2004;Wilderman et al, 2004;Shimura et al, 2007;Swaminathan et al, 2009). These clusters are diverse in organization and function and all appear to have evolved independently (Field and Osbourn, 2008;Frey et al, 2009;Osbourn and Field, 2009;Swaminathan et al, 2009).…”

“…Analysis of the two rice clusters was aided by the fact that expression of these gene clusters is elicitor inducible and by the availability of rice genome sequence information. The oat avenacin cluster was initially defined using forward genetics, facilitated by a simple screen for loss of root fluorescence (Papadopoulou et al, 1999;Qi et al, 2006;Mugford et al, 2009). The thalianol cluster was predicted by searching the genome sequence of Arabidopsis for candidate gene clusters containing triterpene synthase (oxidosqualene cyclase) signature genes and then validated by functional analysis (Field and Osbourn, 2008).…”

A Serine Carboxypeptidase-Like Acyltransferase Is Required for Synthesis of Antimicrobial Compounds and Disease Resistance in Oats

“…Oats (monocots belonging to the genus Avena) produce acylated defense compounds known as avenacins. Avenacins are antimicrobial triterpene glycosides (saponins) that are synthesized in the roots and confer broad-spectrum disease resistance to soil-borne pathogens (Hostettmann and Marston, 1995;Papadopoulou et al, 1999). The ability to synthesize avenacins is restricted to the genus Avena and has evolved since the divergence of oats from other cereals and grasses (Haralampidis et al, 2001;Qi et al, 2004Qi et al, , 2006Mylona et al, 2008).…”

“…This compound has strong fluorescence under ultraviolet illumination due to the presence of the N-methyl anthraniloyl group. Previously, we have exploited this property to screen for reduced root fluorescence mutants of diploid oat (Avena strigosa) that are unable to produce avenacins (Papadopoulou et al, 1999). Avenacin-deficient mutants of A. strigosa are compromised in disease resistance, indicating that avenacins provide protection against microbial attack (Papadopoulou et al, 1999).…”