Abstract
In higher plants, cellulose is synthesized by membrane-spanning large protein complexes named cellulose synthase complexes (CSCs). In this study, the Arabidopsis PASTICCINO2 (PAS2) was identified as an interacting partner of cellulose synthases. PAS2 was previously characterized as the plant 3-hydroxy-acyl-CoA dehydratase, an ER membrane-localized dehydratase that is essential for very-long-chain-fatty acid (VLCFA) elongation. The pas2-1 mutants show defective cell elongation and reduction in cellulose content in both etiolated hypocotyls and light-grown roots. Although disruption of VLCFA synthesis by a genetic alteration had a reduction in VLCFA in both etiolated hypocotyls and light-grown roots, it had a differential effect on cellulose content in the two systems, suggesting the threshold level of VLCFA for efficient cellulose synthesis may be different in the two biological systems. pas2-1 had a reduction in both CSC delivery rate and CSC velocity at the PM in etiolated hypocotyls. Interestingly, Golgi but not post-Golgi endomembrane structures exhibited a severe defect in motility. Experiments using pharmacological perturbation of VLCFA content in etiolated hypocotyls strongly indicate a novel function of PAS2 in the regulation of CSC and Golgi motility. Through a combination of genetic, biochemical and cell biology studies, our study demonstrated that PAS2 as a multifunction protein has an important role in the regulation of cellulose biosynthesis in Arabidopsis hypocotyl.
Highlights
Cellulose is the major load-bearing component of the plant cell walls
This study showed that SmaCCs/microtubule-associate cellulose synthase compartments (MASCs) are critical for fast recovery of cellulose synthase complexes (CSCs) to the plasma membrane after abiotic stress is relieved, and the recovery process is dependent on CSCs-associated protein CSI1
We propose that PAS2 is involved in cellulose synthesis via its direct interactions with cellulose synthase isoforms (CESAs)
Summary
Cellulose is synthesized by plasma membrane-localized rosette-like structures called the cellulose synthase complexes (CSCs) [1,2]. In Arabidopsis, functional CSCs are composed of three distinct cellulose synthase isoforms (CESAs). CSCs specialized for cellulose synthesis in the primary cell wall is composed of CESA1-, CESA3-, CESA6- and CESA6-like proteins [3,4]. For cellulose synthesis in the secondary cell wall, CESA4, CESA7 and CESA8 are essential for secondary CSC formation [5,6,7]. Recent quantification of CESA stoichiometry suggests that CESA isoforms exist in 1:1:1 molecular ratio in both primary and secondary cell wall CSCs [8,9].
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