Disruption of Cortical Microtubules by Overexpression of Green Fluorescent Protein-Tagged a-Tubulin 6 Causes a Marked Reduction in Cell Wall Synthesis

It has been known that the transverse orientation of cortical microtubules （MTs） along the elongation axis is essential for normal cell morphogenesis, but whether cortical MTs are essential for normal cell wall synthesis is still not clear. In the present study, we have investigated whether cortical MTs affect cell wall synthesis by direct alteration of the cortical MT organization in Arabidopsis thaliana. Disruption of the cortical MT organization by expression of an excess amount of green fluorescent protein-tagged a-tubulin 6 （GFP-TUA6） in transgenic Arabidopsis plants was found to cause a marked reduction in cell wall thickness and a de- crease in the cell wall sugars glucose and xylose. Concomitantly, the stem strength of the GFP-TUA6 overexpressors was markedly reduced compared with the wild type. In addition, expression of excess GFP- TUA6 results in an alteration in cell morphogenesis and a severe effect on plant growth and development. Together, these results suggest that the proper organization of cortical MTs is essential for the normal synthesis of plant cell walls.

Overcoming Mycobacterium tuberculosis through small molecule inhibitors to break down cell wall synthesis

Mycobacterium tuberculosis(MTB) utilizes multiple mechanisms to obtain antibiotic resistance during the treatment of infections. In addition, the biofilms, secreted by MTB, can further protect the latter from the contact with drug molecules and immune cells. These self-defending mechanisms lay a formidable challenge to develop effective therapeutic agents against chronic and recurring antibiotictolerant MTB infections. Although several inexpensive and effective drugs(isoniazid, rifampicin, pyrazinamide and ethambutol) have been discovered for the treatment regimen, MTB continues to cause considerable morbidity and mortality worldwide. Antibiotic resistance and tolerance remain major global issues, and innovative therapeutic strategies are urgently needed to address the challenges associated with pathogenic bacteria. Gratifyingly, the cell wall synthesis of tubercle bacilli requires the participation of many enzymes which exclusively exist in prokaryotic organisms. These enzymes, absent in human hepatocytes, are recognized as promising targets to develop anti-tuberculosis drug. In this paper, we discussed the critical roles of potential drug targets in regulating cell wall synthesis of MTB. And also, we systematically reviewed the advanced development of novel bioactive compounds or drug leads for inhibition of cell wall synthesis, including their discovery, chemical modification, in vitro and in vivo evaluation.

GhKNL1 controls fiber elongation and secondary cell wall synthesis by repressing its downstream genes in cotton(Gossypium hirsutum)

Cotton which produces natural fiber materials for the textile industry is one of the most important crops in the world. Class II KNOX proteins are often considered as transcription factors in regulating plant secondary cell wall(SCW) formation. However,the molecular mechanism of the KNOX transcription factor-regulated SCW synthesis in plants(especially in cotton) remains unclear in details so far. In this study, we show a cotton class II KNOX protein(Gh KNL1) as a transcription repressor functioning in fiber development. The Gh KNL1-silenced transgeniccotton produced longer fibers with thicker SCWs,whereas Gh KNL1 dominant repression transgenic lines displayed the opposite fiber phenotype, compared with controls. Further experiments revealed that Gh KNL1 could directly bind to promoters of Gh Ces A4-2/4-4/8-2 and Gh MYB46 for modulating cellulose synthesis during fiber SCW development in cotton. On the other hand, Gh KNL1 could also suppress expressions of Gh EXPA2 D/4 A-1/4 D-1/13 A through binding to their promoters for regulating fiber elongation of cotton. Taken together, these data revealed Gh KNL1 functions in fiber elongation and SCW formation by directly repressing expressions of its target genes related to cell elongation and cellulose synthesis. Thus, our data provide an effective clue for potentially improving fiber quality by genetic manipulation of Gh KNL1 in cotton breeding.

Cryo-EM snapshots of mycobacterial arabinosyltransferase complex EmbB2-AcpM2

Inhibition of Mycobacterium tuberculosis(Mtb)cell wall assembly is an established strategy for anti-TB chemotherapy.Arabinosyltransferase EmbB,which catalyzes the transfer of arabinose from the donor decaprenyl-phosphate-arabinose(DPA)to its arabinosyl acceptor is an essential enzyme for Mtb cell wall synthesis.Analysis of drug resistance mutations suggests that EmbB is the main target of the front-line anti-TB drug,ethambutol.Herein,we report the cryo-EM structures of Mycobacterium smegmatis EmbB in its"resting state"and DPA-bound"active state".EmbB is a fifteen-transmembrane-spanning protein,assembled as a dimer.Each protomer has an associated acyl-carrier-protein(AcpM)on their cytoplasmic surface.Confor-mational changes upon DPA binding indicate an asym-metric movement within the EmbB dimer during catalysis.Functional studies have identified critical residues in substrate recognition and catalysis,and demonstrated that ethambutol inhibits transferase activity of EmbB by competing with DPA.The structures represent the first step directed towards a rational approach for anti-TB drug discovery.