Brassinosteroids Influence Arabidopsis Hypocotyl Graviresponses Through Changes In Mannans And Cellulose

Abstract

Title: 46Brassinosteroids control gravitropism by changing cellulose orientation and mannan 47Highlight 54Our data reveal new functions of cell wall polymers in gravitropic responses. 55Brassinosteroid-related changes in shoot gravitropism uncover that cellulose re-56 organization and mannan content influence shoot mechanical strength and bending. 57 58 Abstract 59 Shoot gravitropism is essential for plants to direct the growth of above-ground tissues 60 towards the soil surface after germination. Brassinosteroids influence shoot gravitropism 61 and we used this as a tool to untangle the function of cell wall polymers during etiolated 62 shoot growth. The ability of etiolated Arabidopsis seedlings to grow upwards was 63 suppressed in the presence of 24-epibrassinolide (EBL) but enhanced in the presence of 64 Brassinazole (BRZ), an inhibitor of brassinosteroid biosynthesis. These effects were 65 accompanied by changes in cell wall mechanics and composition. Cell wall biochemical 66 analyses and confocal microscopy of the cellulose-specific pontamine S4B dye revealed 67 that the EBL and BRZ treatments correlated with changes in cellulose fibre organization 68 and mannan content. Indeed, a longitudinal re-orientation of cellulose fibres supported 69 upright growth whereas the presence of mannans reduced gravitropic bending. The 70 negative effect of mannans on gravitropic bending is a new function for this class of 71 hemicelluloses, and provides insight into evolutionary adaptations by which aquatic 72 ancestors of terrestrial plants colonized land. 73 74

Eudicot primary cell wall glucomannan is related in synthesis, structure, and function to xyloglucan

“…However, the embryo lethality of the Arabidopsis csla7 mutant suggests an important role of glucomannan, at least in embryonic PCWs (Goubet et al, 2003). Recently glucomannan has also been implicated in etiolated hypocotyl gravitropic bending, which involves asymmetric cell expansion (Somssich et al, 2021). In addition, an increase in glucomannan abundance was recently observed in xxt1 xxt2 mutants (Sowinski et al, 2022), which led to the suggestion that other matrix polysaccharides may compensate for a lack of XyG.…”

Seed Priming with Brassinosteroids Alleviates Chromium Stress in Rice Cultivars via Improving ROS Metabolism and Antioxidant Defense Response at Biochemical and Molecular Levels

“…Besides, EBL foliar spray in tomato plants decreased oxidative membrane damage and lipid peroxidation [47]. EBL enhanced the resistance capability of various plants by reducing ROS activity because of enhancing antioxidant activity to scavenge ROS accumulation in plants such as the mung bean, soybean, pea epicotyls, bean, sunflower, and cucumber hypocotyls, Arabidopsis peduncles, and Hordeum vulgare [48][49][50]. Similarly, a recent study demonstrated the protective behavior of EBL towards Zn-induced oxidative damage in Solanum nigrum L. plants [51].…”

Eudicot primary cell wall glucomannan is related in synthesis, structure and function to xyloglucani

“…The structural similarity of β-GGM and XyG led us to hypothesize that they may play connected functions in the cell wall during growth and development. Previously, our knowledge of glucomannan function from Arabidopsis molecular genetics indicated a role limited to seed mucilage and in embryogenesis (Goubet et al, 2003; Goubet et al, 2009; Yu et al, 2014; Voiniciuc et al, 2015; Yu et al, 2018; Somssich et al, 2021). Our results support the idea that XyG conceals the importance of β-GGM in many tissues.…”

“…However, the embryo lethality of the Arabidopsis csla7 mutant suggests an important role of glucomannan, at least in embryonic PCWs (Goubet et al, 2003). Recently glucomannan has also been implicated in etiolated hypocotyl gravitropic bending, which involves asymmetric cell expansion (Somssich et al, 2021). Despite these examples that glucomannan is important in some instances, the role for PCW glucomannan in plant growth and development, and whether that role is related to that of other hemicelluloses, remains obscure.…”