Growth‐ and stress‐related defects associated with wall hypoacetylation are strigolactone‐dependent

Abstract

Mutants affected in the Arabidopsis TBL 29/ ESK 1 xylan O‐acetyltransferase display a strong reduction in total wall O ‐acetylation accompanied by a dwarfed plant stature, collapsed xylem morphology, and enhanced freezing tolerance. A newly identified tbl29/esk1 suppressor mutation reduces the expression of the MAX 4 gene, affecting the biosynthesis of methyl carlactonoate (Me CLA ), an active strigolactone ( SL ). Genetic and biochemical evidence suggests that blocking the biosynthesis of this SL is sufficient to recover all developmental and stress‐related defects associated with the TBL 29/ ESK 1 loss of function without affecting its direct effect—reduced wall O ‐acetylation. Altered levels of the MAX 4 SL biosynthetic gene, reduced branch number, and higher levels of Me CLA , were also found in tbl29/esk1 plants consistent with a constitutive activation of the SL pathway. These results suggest that the reduction in O ‐acetyl substituents in xylan is not directly responsible for the observed tbl29/esk1 phenotypes. Alternatively, plants may perceive defects in the structure of wall polymers and/or wall architecture activating the SL hormonal pathway as a compensatory mechanism.

Genetic dissection of cell wall defects and the strigolactone pathway in Arabidopsis

“…Double mutants were generated by crossing and identified by genotyping of individuals in the F2 generation. Genotyping of T‐DNA lines was performed as described in Ramírez et al., (see for primer sequences). To genotype max2‐1 mutation, the amplicon generated by PCR using max2‐1F/max2‐1 R primer combination was digested with ApoI restriction enzyme resulting in a 147 bp single fragment in wildtype plants and two fragments (76 and71 bp) in mutant plants.…”

“…Xylem morphology was evaluated as described in Ramírez et al. (). Equivalent segments of plant stems from the various genotypes were used to prepare hand‐cut sections.…”

“…Total destarched alcohol‐insoluble residue was prepared and cellulose content, matrix polysaccharide composition, and total wall acetate were determined according to Foster, Martin, and Pauly () as described in Ramírez et al. ().…”

“…How KAK, a putative ubiquitin E3 ligase involved in endoreduplication and control of DNA content in trichomes, regulates xylem development remains elusive (Bensussan et al., ; Downes, Stupar, Gingerich, & Vierstra, ; El Refy et al., ). In another case, mutations in MAX4 similarly rescue tbl29 collapsed xylem, dwarfism, and increased freezing tolerance (Ramírez, Xiong, Mashiguchi, Yamaguchi, & Pauly, ). MAX4 encodes a key enzyme in SL biosynthesis (Sorefan et al., ), suggesting that the tbl29 ‐triggered irx syndrome is SL‐dependent.…”

“…This requirement was further confirmed by the chemical complementation assays using a synthetic SL (i.e., GR‐24). tbl29 max4 double mutant plants growing in the presence of GR‐24 exhibit collapsed xylem and dwarfed stature, indicating that complementing the SL deficiency with exogenous applications of SL circumvent the max4 effect (Ramírez et al., ).…”