Suppression of dwarf and Irregular Xylem phenotypes generates low-acetylated biomass lines in arabidopsis

Abstract

Eskimo1-5 (esk1-5) isadwarfArabidopsis (Arabidopsis thaliana)mutant that has a constitutive drought syndrome and collapsed xylem vessels, alongwithlowacetylation levels inxylan andmannan.ESK1has xylanO-acetyltransferase activity in vitro.Weusedasuppressor strategyon esk1-5 to screen for variantswithwild-type growth and lowacetylation levels, a favorable combination for ethanol production.We found a recessive mutation in the KAKTUS (KAK) gene that suppressed dwarfism and the collapsed xylem character, the cause of decreased hydraulic conductivity in the esk1-5 mutant. Backcrosses between esk1-5 and two independent knockout kak mutants confirmed suppression of the esk1-5 effect. kak single mutants showed larger stem diameters than the wild type. The KAK promoter fused with a reporter geneshowedactivity in the vascular cambium,phloem,andprimary xylem inthe stemandhypocotyl.However, suppression of the collapsed xylem phenotype in esk1 kak double mutantswas not associatedwith the recovery of cell wallO-acetylation or anymajor cell wall modifications. Therefore, our results indicate that, in addition to its described activity as a repressor of endoreduplication, KAKmay play a role in vascular development. Furthermore, orthologous esk1 kak double mutantsmay hold promise for ethanol production in crop plants.