Cellulose synthesis in land plants

All plant cells are surrounded by a cell wall that provides cohesion,protection,and a means of directional growth to plants.Cellulose microfibrils contribute the main biomechanical scaffold for most of these walls.The biosynthesis of cellulose,which typically is the most prominent constituent of the cell wall and therefore Earth’s most abundant biopolymer,is finely attuned to developmental and environmental cues.Our understanding of the machinery that catalyzes and regulates cellulose biosynthesis has substantially improved due to recent technological advances in,for example,structural biology and microscopy.Here,we provide a comprehensive overview of the structure,function,and regulation of the cellulose synthesis machinery and its regulatory interactors.We aim to highlight important knowledge gaps in the field,and outline emerging approaches that promise a means to close those gaps.

Stem Cell Regulation by Arabidopsis WOX Genes

Gene amplification followed by functional diversification is a major force in evolution. A typical example of this is seen in the WUSCHEL-RELATED HOMEOBOX （WOX） gene family, named after the Arabidopsis stem cell regulator WUSCHEL. Here we analyze functional divergence in the WOX gene family. Members of the WUS clade, except the cambium stem cell regulator WOX4, can substitute for WUS function in shoot and floral stem cell maintenance to different degrees. Stem cell function of WUS requires a canonical WUS-box, essential for interaction with TPL/TPR co-repressors, whereas the repressive EAR domain is dispensable and the acidic domain seems only to be required for female fertility. In contrast to the WUS clade, members of the ancient WOX13 and the WOX9 clades cannot support stem cell maintenance. Although the homeodomains are interchangeable between WUS and WOX9 clade members, a WUS- compatible homeodomain together with canonical WUS-box is not sufficient for stem cell maintenance. Our results suggest that WOX function in shoot and floral meristems of Arabidopsis is restricted to the modern WUS clade, suggesting that stem cell control is a derived function. Yet undiscovered functional domains in addition to the homeodomain and the WUS-box are necessary for this function.

SNOWY COTYLEDON 2 Promotes Chloroplast Development and Has a Role in Leaf Variegation in Both Lotus japonicus and Arabidopsis thaliana

Plants contain various factors that transiently interact with subunits or intermediates of the thylakoid multiprotein complexes, promoting their stable association and integration. Hence, assembly factors are essential for chloroplast development and the transition from heterotrophic to phototrophic growth. Snowy cotyledon 2 （SCO2） is a DNAJ-like protein involved in thylakoid membrane biogenesis and interacts with the light-harvesting chlorophyll-binding protein LHCBI. In Arabidopsis thaliana, SCO2 function was previ- ously reported to be restricted to cotyledons. Here we show that disruption of SC02 in Lotus japonicus results not only in paler cotyledons but also in variegated true leaves. Furthermore, smaller and pale- green true leaves can also be observed in A. thaliana sco2 （atsco2） mutants under short-day conditions. In both species, SCO2 is required for proper accumulation of PSlI-LHCll complexes. In contrast to other variegated mutants, inhibition of chloroplastic translation strongly affects L. japonicus sco2 mutant devel- opment and fails to suppress their variegated phenotype. Moreover, inactivation of the suppressor of variegation AtClpR1 in the atsco2 background results in an additive double-mutant phenotype with variegated true leaves. Taken together, our results indicate that SCO2 plays a distinct role in PSll assembly or repair and constitutes a novel factor involved in leaf variegation.

Salt with a sweet tooth:galactan synthesis impacts salt tolerance in Arabidopsis

Abiotic stresses result in the loss of millions of dollars'worth of agricultural crops each year(Munns and Tester,2008).The accumulation of sodium chloride in soils is a prominent abiotic stress and poses significant challenges to farmers(Munns et al.,2020).Moreover,soil salinity is predicted to worsen with the rise in global temperatures and depletion of groundwater resources.