Control of secondary cell wall formation by Musashi-type translational regulators in trees.

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Fouassier, Hélène | Kairouani, Alicia | Pontier, D. | Picart, C. | Martinez, Y | Le Bot, Lucie | Fanuel, Mathieu | Hammann, Philippe | Belmudes, Lucid | Merret, Rémy | Azevedo-Favory, Jacinthe | Carpentier, Marie-Christine | D., Gagliardi | Couté, Y. | Sibout, Richard | Bies-Etheve, N. | Lagrange, Thierry | Mounet, Fabien

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International audience. Deciphering the mechanism of secondary cell wall (SCW) formation in plants is crucialto understand their development, their plasticity in response to environment and themolecular basis of biomass recalcitrance. Although transcriptional regulation isessential for SCW formation, little is known about the implication of post-transcriptionalmechanisms in this process. In a recent publication, Kairouani et al. characterized thefunction of two bonafide RNA-binding proteins homologous to the animal translationalregulator Musashi (MSIL)1. They demonstrated that MSIL proteins belong to amultigenic family of 4 members and control SCW formation in Arabidopsis. MSILsmutation alter SCW formation in the fibers and decrease stem rigidity. This phenotypewas associated to a reduction in lignin deposition, and an increase of 4-Oglucuronoxylanmethylation. In accordance, quantitative proteomics of stems reveal anoveraccumulation of glucuronoxylan biosynthetic machinery, including GXM3, in themsil2/4 mutant stem. We showed that MSIL4 immunoprecipitates GXM mRNAs,suggesting a novel aspect of SCW regulation, linking post-transcriptional control to theregulation of SCW biosynthesis genes. We identified several close orthologs of AtMSILgenes in trees genome which are preferentially expressed in stem tissues. Within theframework of the ANR project MusaWALL, we started to investigate the function ofMSIL-like proteins in Eucalyptus using CRISPR-Cas9 mutants and overexpressors.

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