Evolutionary Conserved Function of Barley and Arabidopsis 3-KETOACYL-CoA SYNTHASES in Providing Wax Signals for Germination of Powdery Mildew Fungi    

Abstract

For plant pathogenic fungi, such as powdery mildews, that survive only on a limited number of host plant species, it is a matter of vital importance that their spores sense that they landed on the right spot to initiate germination as quickly as possible. We investigated a barley (Hordeum vulgare) mutant with reduced epicuticular leaf waxes on which spores of adapted and nonadapted powdery mildew fungi showed reduced germination. The barley gene responsible for the mutant wax phenotype was cloned in a forward genetic screen and identified to encode a 3-KETOACYL-CoA SYNTHASE (HvKCS6), a protein participating in fatty acid elongation and required for synthesis of epicuticular waxes. Gas chromatography-mass spectrometry analysis revealed that the mutant has significantly fewer aliphatic wax constituents with a chain length above C-24. Complementation of the mutant restored wild-type wax and overcame germination penalty, indicating that wax constituents less present on the mutant are a crucial clue for spore germination. Investigation of Arabidopsis (Arabidopsis thaliana) transgenic plants with sense silencing of Arabidopsis REQUIRED FOR CUTICULAR WAX PRODUCTION1, the HvKCS6 ortholog, revealed the same germination phenotype against adapted and nonadapted powdery mildew fungi. Our findings hint to an evolutionary conserved mechanism for sensing of plant surfaces among distantly related powdery mildews that is based on KCS6-derived wax components. Perception of such a signal must have been evolved before the monocot-dicot split took place approximately 150 million years ago.

Endophytic fungus Falciphora oryzae promotes lateral root growth by producing indole derivatives after sensing plant signals

“…Our RNA sequencing data indicated that CUT1 ( REQUIRED FOR CUTICULAR WAX PRODUCTION1 ), the biosynthetic gene for the cutin monomer, was induced after cocultivation, whereas pathways for other known plant signals (strigolactone, flavonoid, and 2‐hydroxy fatty acid) were not significantly altered. In addition, the cutin monomer was reported that can initiate the germination of nonadapted powdery mildew fungi (Weidenbach et al, ). These results suggested that the cutin monomer could be a possible plant signal perceived by F. oryzae , but this still awaits future experimental confirmation.…”

The Genes Bm2 and Blmc that Affect Epicuticular Wax Deposition in Sorghum are Allelic

“…Furthermore, EW mutants in barley and Arabidopsis, Arabidopsis thaliana (L.) Heynh, had reduced germination of powdery mildew (Blumeria graminis f. sp. hordei, Bgh race K1) spores as compared with wild-type plants, likely because of a reduction in the amount of C-26 aldehyde (hexacosanal), a component of the EW (Weidenbach et al, 2014). A similar result was observed in the EW mutant irg1/palm1 of Medicago truncatula Gartner, which had reduced anthracnose (Colletotrichum trifolii Bain et Essary) and nonhost rust pathogen (Phakopsora pachyrhizi Syd.…”

“…For example, the bloomless sorghum near-isogenic lines had greater in vitro dry matter digestibilities than the recurrent parents, suggesting a potential benefit of less EW for ruminants (Cummins and Dobson, 1972). hordei, Bgh race K1) spores as compared with wild-type plants, likely because of a reduction in the amount of C-26 aldehyde (hexacosanal), a component of the EW (Weidenbach et al, 2014). Furthermore, EW mutants in barley and Arabidopsis, Arabidopsis thaliana (L.) Heynh, had reduced germination of powdery mildew (Blumeria graminis f. sp.…”

Translational genomics using Arabidopsis as a model enables the characterization of pennycress genes through forward and reverse genetics

“…In addition to undesirable traits, the selected mutants may also carry additional desirable mutations. For example, under certain circumstances mutations in wax biosynthesis can be deemed desirable as there have been reported associations between reductions in epidermal wax and enhanced disease resistance or water usage (Uppalapati et al ., ; Weidenbach et al ., , ). Wax production has been well studied in A. thaliana (Millar et al ., ; Joubès et al ., ; Kim et al ., ) and found to be modulated by genes such as ketoacyl‐CoA synthase (KCS), β‐ketoacyl‐CoA reductase (KCR) and enoyl‐CoA reductase (ECR).…”