Abstract

Defects in the biosynthesis and/or deposition of secondary plant cell wall polymers result in the collapse of xylem vessels causing a dwarfed plant stature and an altered plant architecture termed irregular xylem (irx) syndrome. For example, reduced xylan O‐acetylation causes strong developmental defects and increased freezing tolerance. Recently, we demonstrated that the irx syndrome in the trichome birefringence‐like 29/eskimo1 (tbl29/esk1) mutant is dependent on MORE AXILLARY GROWTH 4 (MAX4), a key enzyme in the biosynthesis of the phytohormone strigolactone (SL). In this report, we show that other xylan‐ and cellulose‐deficient secondary wall mutants exhibit increased freezing tolerance correlated with the irx syndrome. In addition, these phenotypes are also dependent on MAX4, suggesting a more general interaction between secondary wall defects and SL biosynthesis. In contrast, MAX4 does not play a role in developmental defects triggered by primary wall deficiencies, suggesting that the interaction is restricted to vascular tissue. Through a reverse genetics approach, the requirement of different components of the SL pathway impacting the irx syndrome in tbl29 was evaluated. Our results show that the tbl29‐associated irx phenotypes are dependent on the MAX3 and MAX4 enzymes, involved in the early steps of SL biosynthesis. In contrast, this signaling is independent on downstream enzymes in the biosynthesis and perception of SL such as MAX1 and MAX2.

Highlights

  • Xylem elements are surrounded by a secondary wall composed mainly of cellulose, xylan and lignin, conferring unique physiochemical properties to these specialized cells

  • In the first step of the SL biosynthesis, a plastid-localized β-carotene isomerase (AtD27 in Arabidopsis) converts all-trans-β-carotene into 9-cis-β-carotene, which is used as substrate to generate carlactone by the consecutive action of two carotenoid-cleavage dioxygenase (CCD) enzymes, CCD7/MAX3/RMS5/D17/DAD3 and CCD8/MAX4/RMS1/D10/DAD1 (Schwartz et al, 2004; Alder et al, 2012; Waters et al, 2012)

  • Arabidopsis TDNA insertion lines were obtained for genes involved in the synthesis of cellulose, xylan and lignin

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Summary

Introduction

Xylem elements are surrounded by a secondary wall composed mainly of cellulose, xylan and lignin, conferring unique physiochemical properties to these specialized cells. Reduction of xylan O-acetylation in tbl29/esk mutant plants causes drastic xylem collapse accompanied by dwarfism and constitutive tolerance to freezing, drought and salt stresses (Xin and Browse, 1998; Xin et al, 2007; Lefebvre et al, 2011; Bouchabke-Coussa et al, 2008; Xiong et al, 2013) These phenotypes seem not to be a direct consequence of the defective secondary wall composition/structure, as two suppressor lines have been identified exhibiting rescued developmental- and stress-related phenotypes while the low xylan Oacetylation content was unchanged. Upon D14MeCLA interaction, D14 returns to the initial conformation inducing the hydrolytic degradation of MeCLA and restoring the system after signal transmission (Seto et al, 2019)

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