plants Article The Orchid Velamen: A Model System for Studying Patterned Article SecondaryArticle Cell Wall Development? The Orchid Velamen:Velamen: AA ModelModel SystemSystem forfor StudyingStudying PatternedPatterned 1,2 3 3 2,3,4,5, Nurul A. IdrisSecondary , Maketelana Aleamotu Cell ʻ a , WallDavid. W Development?McCurdyDevelopment? and David A. Collings * 1 Faculty of Science and Marine Environment, Universiti Malaysia Terengganu, Kuala Terengganu 21030, Nurul A. Idris 1,2Malaysia, ,Maketelana Maketelana; [email protected] Aleamotu Aleamotu ʻ a a3 3,, DavidDavid. W. W McCurdyMcCurdy 33 andand David David A. A. Collings Collings 2,3,4,52,3,4,5,,* * 2 School of Biological Science, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand 3 School of Environmental and Life Sciences, The University of Newcastle, Callaghan, NSW 2308, Australia; [email protected] FacultyFaculty of of Sc(M.A.); Scienceience [email protected] and and Marine Marine Environment, Environment, Universiti Universiti (D.W.M.) Malaysia Malaysia Terengganu, Terengganu, Kuala Terengganu 21030, 4 School of Molecular Sciences,MalaysiaKuala TerengganuThe; [email protected] University 21030, of Western Malaysia; Australia, [email protected] Crawley, WA 6009, Australia 5 Harry Butler Institute,22 School SchoolMurdoch of of BiologicalUniversity, Biological Science, Murdoch Science, University, UniversityWA 6150, Australiaof of Canterbury, Canterbury, Private Private Bag Bag 4800 4800,, Christchurch Christchurch 8140, 8140, New New Zealand Zealand * Correspondence: [email protected] 33 SchoolSchool of of Environmental Environmental and and Life Life Sciences, Sciences, The The University University of of Newcastle, Newcastle, Callaghan, Callaghan, NSW NSW 2308, 2308, Australia Australia;; [email protected]@uon.edu.au (M.A.); (M.A.); [email protected] [email protected] (D.W.M.) (D.W.M.) Abstract: Understanding the mechanisms through which plants generate secondary cell walls is of 44 SchoolSchool of of Molecular Molecular Sciences, Sciences, The The University University of of Western Western Australia, Australia, Crawley Crawley,, WA WA 6009 6009,, Australia more than academic55 interest:HarryHarry Butler Butlerthe physi Institute, Institute,cal properties Murdoch Murdoch University,of University, plant-derived Murdoch Murdoch, materials, WA WA 6150,, 6150, including Australia Australia timber and textiles, all depend* Correspondence:Correspondence: upon secondary [email protected] [email protected] cellulose organization. Processes controlling cellulose in the secondary cell wall and their reliance on microtubules have been documented in recent dec- ades, but this understandingAbstract: is Understanding complicated, as secondarythe mechanisms walls normally through form which in the plants plant’s generate interior secondary cell wall wallss is of where live cell imaging is more difficult. We investigated secondary wall formation in the orchid more than academicacademic interest:interest: the the physical physical properties properties of of plant-derived plant-derived materials, materials including, including timber timber and velamen, a multicellular epidermal layer found around orchid roots that consists of dead cells with andtextiles, textiles all depend, all depend upon upon secondary secondary wall cellulosewall cellulose organization. organization. Processes Processes controlling controlling cellulose cellulose in the lignified secondary cell walls. The patterns of cell wall ridges that form within the velamen vary between different orchidinsecondary the secondaryspecies, cell but wall cellimmunolabelling and wall their and reliance their demonstrated reliance on microtubules on thatmicrotubules wall have deposition been have documented isbeen con- documented in recent in decades, recent de butc- Citation: Idris, N.A.; Aleamotu ʻ a, trolled by microtubules.ades,this understanding butAs thesethis understanding patterning is complicated, events is complicatedoccur as at secondarythe outer, as secondary surface walls of normally wallsthe root, normally form and as in form the plant’s in the plant’s interior interior where M.; McCurdy, D.W.; Collings, D.A. orchids are adaptablewherelive for cell tissuelive imaging cell culture imaging is and more genetic is difficult. more manipulation, difficult. We investigated We we investigatedconclude secondary that thesecondary wallorchid formation root wall formation in the orchid in the velamen, orchid The Orchid Velamen: A Model Sys- velamen may indeedvelamen,amulticellular be a suitable a multicellular model epidermal system epidermallayer for studying found layer the around found organization orchid around rootsof otherchid plant that roots consistscell wall. thatof consists dead cells of dead with cells lignified with tem for Studying Patterned Second- Notably, roots of thelignifiedsecondary commonly secondary cell grown walls. orchid cell The walls.Laelia patterns anceps The patterns ofappear cell wallideally of cell ridges suited wall that for ridges developing form that within form this the within velamen the velamen vary between vary ary Cell Wall Development? Plants Citation: Idris, N.A.;research. Aleamotu ʻ a, betweendifferent different orchid species, orchid butspecies, immunolabelling but immunolabelling demonstrated demonstrated that wall that deposition wall deposition is controlled is con- by 2021, 10, x. M.; McCurdy, D.W.; Collings, D.A. https://doi.org/10.3390/xxxxxCitation: Idris, N.A.; Aleamotu ʻ a, trolledmicrotubules. by microtubules. As these patterning As these patterning events occur events at the occur outer at surface the outer of thesurface root, of and the as root, orchids and are as The Orchid Velamen:Keywords: A Model lignin; lignification; microtubules; orchid velamen; secondary cell wall M.; McCurdy, D.W.; Collings, D.A. orchidsadaptable are for adaptable tissue culture for tissue and geneticculture manipulation,and genetic manipulation, we conclude thatwe conclude the orchid that root the velamen orchid mayroot System for Studying Patterned Academic Editors: ViktorThe Orchid Demko Velamen:, Ján A Model Sys- velamenindeed be may a suitable indeed model be a suitable system model for studying system the for organization studying the of organization the plant cell of wall. the plant Notably, cell rootswall. Secondary Cell Wall Development? Jásik, Alexander Luxtem and for Marek Studying Vac- Patterned Second- Notably, roots of the commonly grown orchid Laelia anceps appear ideally suited for developing this Plants 2021, 10, 1358. https:// of the commonly grown orchid Laelia anceps appear ideally suited for developing this research. ulík ary Cell Wall Development? Plants doi.org/10.3390/plants100713581. Introduction research. ʻ 2021, 10, x. Received: 6 June 2021 The primaryKeywords: componentlignin; of the lignification;plant cell wall microtubules; is cellulose, orchida β-1,4 velamen;polymer secondaryof D-glu- cell wall https://doi.org/10.3390/xxxxx Accepted: 24 June 2021Academic Editors: Viktorcose Demko, crystallized Keywords:into microfibrils lignin; that lignification; contain 18 m(toicrotubules; 24) separate orchid glucan velamen; chains [1,2secondary]. The cell wall Published: 2 July 2021Ján Jásik, Alexander Luxorganization and of this cellulose within the cell wall controls plant morphogenesis: for plant Academic Editors: Viktor Demko, Ján Marek Vaculík cells undergoing expansion with a thin, deformable primary cell wall, the transverse ori- Jásik, Alexander Lux and Marek Vac- Publisher’s Note: MDPI stays neu- entation of the cellulose1. Introduction microfibrils dictates the biophysical properties of the wall and tral with regard ulíkto jurisdictional Received: 6 June 2021limits expansion to a direction perpendicular to the microfibrils [3]. In mature, nonex- claims in published maps and institu- 1. IntroductionThe primary component of the plant cell wall is cellulose, a β-1,4 polymer of D-glucose Accepted: 24 June 2021panding plant cells, cellulose is instead organized into oblique or cross-laminate patterns tional affiliations. crystallized into microfibrils that contain 18 (to 24) separate glucan chains [1,2]. The organi- Received: 6 June 2021that prevent further expansion.The primary A subset component of plant cells, of the however, plant cell develop wall ais secondary cellulose, cell a β-1,4 polymer of D-glu- Published: 2 July 2021 zation of this cellulose within the cell wall controls plant morphogenesis: for plant cells Accepted: 24 June 2021wall in which extracose cellulose crystallized is reinforced into microfibrils with the organic that containpolymer 18lignin (to 24)[4,5 ].separate In these glucan chains [1,2]. The Published: 2 July 2021secondary walls,organizationundergoing the organization expansion of thisof the cellulose cellulose with a thin,within again deformable remainsthe cell criticalwall primary controls for the cell strength plant wall, morphogenesis: the transverse orientation for plant Publisher’s Note: MDPI stays neutral of the cell walls, andcellsof the thus undergoing cellulose of the overall microfibrils expansion plant tissue dictates with [3 a]. thin, theThese biophysical deformable secondary propertiescell primary walls are cell of of the wall, wall the and transverse limits expan- ori- Copyright: © 2021 bywith the regardauthors. to Li- jurisdictional claims in Publisher’s Note: MDPI