scholarly journals Knockdown of Arabidopsis ROOT UVB SENSITIVE4 Disrupts Anther Dehiscence by Suppressing Secondary Thickening in the Endothecium

2019 ◽  
Vol 60 (10) ◽  
pp. 2293-2306 ◽  
Author(s):  
Shu-Qing Zhao ◽  
Wen-Chao Li ◽  
Yi Zhang ◽  
Alison C Tidy ◽  
Zoe A Wilson
Keyword(s):  
Cell Wall ◽  
Secondary Wall ◽  
Secondary Cell Wall ◽  
Transcript Abundance ◽  
Myb Transcription Factor ◽  
Wall Thickening ◽  
Floral Buds ◽  
Highly Active ◽  
Secondary Thickening ◽  
Secondary Wall Thickening

Abstract ROOT UV-B SENSITIVE4 (RUS4) encodes a protein with no known function that contains a conserved Domain of Unknown Function 647 (DUF647). The DUF647-containing proteins RUS1 and RUS2 have previously been associated with root UV-B-sensing pathway that plays a major role in Arabidopsis early seedling morphogenesis and development. Here, we show that RUS4 knockdown Arabidopsis plants, referred to as amiR-RUS4, were severely reduced in male fertility with indehiscent anthers. Light microscopy of anther sections revealed a significantly reduced secondary wall thickening in the endothecium of amiR-RUS4 anthers. We further show that the transcript abundance of the NAC domain genes NAC SECONDARY WALL THICKENING PROMOTING FACTOR1 (NST1) and NST2, which have been shown to regulate the secondary cell wall thickenings in the anther endothecium, were dramatically reduced in the amiR-RUS4 floral buds. Expression of the secondary cell wall-associated MYB transcription factor genes MYB103 and MYB85 were also strongly reduced in floral buds of the amiR-RUS4 plants. Overexpression of RUS4 led to increased secondary thickening in the endothecium. However, the rus4-2 mutant exhibited no obvious phenotype. Promoter-GUS analysis revealed that the RUS4 promoter was highly active in the anthers, supporting its role in anther development. Taken together, these results suggest that RUS4, probably functions redundantly with other genes, may play an important role in the secondary thickening formation in the anther endothecium by indirectly affecting the expression of secondary cell wall biosynthetic genes.

scholarly journals THE FINE STRUCTURE OF DIFFERENTIATING XYLEM ELEMENTS

1965 ◽  
Vol 24 (3) ◽  
pp. 415-431 ◽  
Author(s):  
James Cronshaw ◽  
G. Benjamin Bouck
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Wall ◽  
Fine Structure ◽  
Secondary Wall ◽  
Osmium Tetroxide ◽  
Light And Electron Microscopy ◽  
Wall Thickening ◽  
Direction Parallel ◽  
Secondary Wall Thickening ◽  
Xylem Elements

Differentiating xylem elements of Avena coleoptiles have been examined by light and electron microscopy. Fixation in 2 per cent phosphate-buffered osmium tetroxide and in 6 per cent glutaraldehyde, followed by 2 per cent osmium tetroxide, revealed details of the cell wall and cytoplasmic fine structure. The localized secondary wall thickening identified the xylem elements and indicated their state of differentiation. These differentiating xylem elements have dense cytoplasmic contents in which the dictyosomes and elements of rough endoplasmic reticulum are especially numerous. Vesicles are associated with the dictyosomes and are found throughout the cytoplasm. In many cases, these vesicles have electron-opaque contents. "Microtubules" are abundant in the peripheral cytoplasm and are always associated with the secondary wall thickenings. These microtubules are oriented in a direction parallel to the microfibrillar direction of the thickenings. Other tubules are frequently found between the cell wall and the plasma membrane. Our results support the view that the morphological association of the "microtubules" with developing cell wall thickenings may have a functional significance, especially with respect to the orientation of the microfibrils. Dictyosomes and endoplasmic reticulum may have a function in some way connected with the synthetic mechanism of cell wall deposition.

scholarly journals Histone methyltransferase ATX1 dynamically regulates fiber secondary cell wall biosynthesis in Arabidopsis inflorescence stem

2020 ◽  
Author(s):  
Xianqiang Wang ◽  
Denghui Wang ◽  
Wenjian Xu ◽  
Lingfei Kong ◽  
Xiao Ye ◽  
...  
Keyword(s):  
Cell Wall ◽  
Secondary Wall ◽  
Histone Methyltransferase ◽  
Epigenetic Mechanism ◽  
Wall Thickening ◽  
Loss Of Function ◽  
Inflorescence Stem ◽  
Secondary Wall Thickening ◽  
Cell Wall Development ◽  
Stem Development

Abstract Secondary wall thickening in the sclerenchyma cells is strictly controlled by a complex network of transcription factors in vascular plants. However, little is known about the epigenetic mechanism regulating secondary wall biosynthesis. In this study, we identified that ARABIDOPSIS HOMOLOG of TRITHORAX1 (ATX1), a H3K4-histone methyltransferase, mediates the regulation of fiber cell wall development in inflorescence stems of Arabidopsis thaliana. Genome-wide analysis revealed that the up-regulation of genes involved in secondary wall formation during stem development is largely coordinated by increasing level of H3K4 tri-methylation. Among all histone methyltransferases for H3K4me3 in Arabidopsis, ATX1 is markedly increased during the inflorescence stem development and loss-of-function mutant atx1 was impaired in secondary wall thickening in interfascicular fibers. Genetic analysis showed that ATX1 positively regulates secondary wall deposition through activating the expression of secondary wall NAC master switch genes, SECONDARY WALL-ASSOCIATED NAC DOMAIN PROTEIN1 (SND1) and NAC SECONDARY WALL THICKENING PROMOTING FACTOR1 (NST1). We further identified that ATX1 directly binds the loci of SND1 and NST1, and activates their expression by increasing H3K4me3 levels at these loci. Taken together, our results reveal that ATX1 plays a key role in the regulation of secondary wall biosynthesis in interfascicular fibers during inflorescence stem development of Arabidopsis.

scholarly journals SECONDARY WALL ASSOCIATED MYB1 is a positive regulator of secondary cell wall thickening in Brachypodium distachyon and is not found in the Brassicaceae

2018 ◽  
Vol 96 (3) ◽  
pp. 532-545 ◽  
Author(s):  
Pubudu P. Handakumbura ◽  
Kathryn Brow ◽  
Ian P. Whitney ◽  
Kangmei Zhao ◽  
Karen A. Sanguinet ◽  
...  
Keyword(s):  
Cell Wall ◽  
Secondary Wall ◽  
Secondary Cell Wall ◽  
Brachypodium Distachyon ◽  
Wall Thickening ◽  
Positive Regulator ◽  
Secondary Cell Wall Thickening

scholarly journals Arabidopsis XTH4 and XTH9 contribute to wood cell expansion and secondary wall formation

2019 ◽  
Author(s):  
Sunita Kushwah ◽  
Alicja Banasiak ◽  
Nobuyuki Nishikubo ◽  
Marta Derba-Maceluch ◽  
Mateusz Majda ◽  
...  
Keyword(s):  
Cell Wall ◽  
Cell Expansion ◽  
Cell Walls ◽  
Secondary Wall ◽  
Secondary Xylem ◽  
Cell Wall Integrity ◽  
Wall Thickening ◽  
Xylem Cell ◽  
Secondary Wall Thickening ◽  
Secondary Wall Formation

ABSTRACTIn dicotyledons, xyloglucan is the major hemicellulose of primary walls affecting the load-bearing framework with participation of XTH enzymes. We used loss- and gain-of function approaches to study functions of abundant cambial region expressed XTH4 and XTH9 in secondary growth. In secondarily thickened hypocotyls, these enzymes had positive effects on vessel element expansion and fiber intrusive growth. In addition, they stimulated secondary wall thickening, but reduced secondary xylem production. Cell wall analyses of inflorescence stems revealed changes in lignin, cellulose, and matrix sugar composition, indicating overall increase in secondary versus primary walls in the mutants, indicative of higher xylem production compared to wild type (since secondary walls were thinner). Intriguingly, the number of secondary cell wall layers was increased in xth9 and reduced in xth4, whereas the double mutant xth4x9 displayed intermediate number of layers. These changes correlated with certain Raman signals from the walls, indicating changes in lignin and cellulose. Secondary walls were affected also in the interfascicular fibers where neither XTH4 nor XTH9 were expressed, indicating that these effects were indirect. Transcripts involved in secondary wall biosynthesis and in cell wall integrity sensing, including THE1 and WAK2, were highly induced in the mutants, indicating that deficiency in XTH4 and XTH9 triggers cell wall integrity signaling, which, we propose, stimulates the xylem cell production and modulates secondary wall thickening. Prominent effects of XTH4 and XTH9 on secondary xylem support the hypothesis that altered xyloglucan can affect wood properties both directly and via cell wall integrity sensing.SIGNIFICANCE STATEMENTXyloglucan is a ubiquitous component of primary cell walls in all land plants but has not been so far reported in secondary walls. It is metabolized in muro by cell wall-residing enzymes - xyloglucan endotransglycosylases/hydrolases (XTHs), which are reportedly abundant in vascular tissues, but their role in these tissues is unclear. Here we report that two vascular expressed enzymes in Arabidopsis, XTH4 and XTH9 contribute to the secondary xylem cell radial expansion and intrusive elongation in secondary vascular tissues.Unexpectedly, deficiency in their activities highly affect chemistry and ultrastructure of secondary cell walls by non-cell autonomous mechanisms, including transcriptional induction of secondary wall-related biosynthetic genes and cell wall integrity sensors. These results link xyloglucan metabolism with cell wall integrity pathways, shedding new light on previous reports about prominent effects of xyloglucan metabolism on secondary walls.One sentence summaryXTH4 and XTH9 positively regulate xylem cell expansion and fiber intrusive tip growth, and their deficiency alters secondary wall formation via cell wall integrity sensing mechanisms.

scholarly journals Mitogen-activated protein kinase 6 negatively regulates secondary wall biosynthesis by modulating MYB46 protein stability in Arabidopsis thaliana

PLoS Genetics ◽  
2021 ◽  
Vol 17 (4) ◽  
pp. e1009510
Author(s):  
Jong Hee Im ◽  
Jae-Heung Ko ◽  
Won-Chan Kim ◽  
Brent Crain ◽  
Daniel Keathley ◽  
...  
Keyword(s):  
Cell Wall ◽  
Protein Kinase ◽  
Translational Regulation ◽  
Secondary Wall ◽  
Secondary Cell Wall ◽  
Specific Activity ◽  
Mitogen Activated Protein Kinase ◽  
Myb Transcription Factor ◽  
In Planta ◽  
Mitogen Activated Protein

The R2R3-MYB transcription factor MYB46 functions as a master switch for secondary cell wall biosynthesis, ensuring the exquisite expression of the secondary wall biosynthetic genes in the tissues where secondary walls are critical for growth and development. At the same time, suppression of its function is needed when/where formation of secondary walls is not desirable. Little is known about how this opposing control of secondary cell wall formation is achieved. We used both transient and transgenic expression of MYB46 and mitogen-activated protein kinase 6 (MPK6) to investigate the molecular mechanism of the post-translational regulation of MYB46. We show that MYB46 is phosphorylated by MPK6, leading to site specific phosphorylation-dependent degradation of MYB46 by the ubiquitin-mediated proteasome pathway. In addition, the MPK6-mediated MYB46 phosphorylation was found to regulate in planta secondary wall forming function of MYB46. Furthermore, we provide experimental evidences that MYB83, a paralog of MYB46, is not regulated by MPK6. The coupling of MPK signaling to MYB46 function provides insights into the tissue- and/or condition-specific activity of MYB46 for secondary wall biosynthesis.

The R2R3 MYB transcription factor MYB189 negatively regulates secondary cell wall biosynthesis in Populus

2019 ◽  
Vol 39 (7) ◽  
pp. 1187-1200 ◽  
Author(s):  
Bo Jiao ◽  
Xin Zhao ◽  
Wanxiang Lu ◽  
Li Guo ◽  
Keming Luo
Keyword(s):  
Cell Wall ◽  
Transcription Factor ◽  
Secondary Wall ◽  
Secondary Cell Wall ◽  
Populus Trichocarpa ◽  
Wood Formation ◽  
Myb Transcription Factor ◽  
Polymerase Chain ◽  
Xylem Fibers ◽  
R2r3 Myb

Abstract Secondary cell wall (SCW) biosynthesis during wood formation in trees is controlled by a multilevel regulatory network that coordinates the expression of substantial genes. However, few transcription factors involved in the negative regulation of secondary wall biosynthesis have been characterized in tree species. In this study, we isolated an R2R3 MYB transcription factor MYB189 from Populus trichocarpa, which is expressed predominantly in secondary vascular tissues, especially in the xylem. A novel repression motif was identified in the C-terminal region of MYB189, which indicates this factor was a transcriptional repressor. Overexpression (OE) of MYB189 in Arabidopsis and poplar resulted in a significant reduction in the contents of lignin, cellulose and hemicelluloses. Vascular development in stems of MYB189 OE lines was markedly inhibited, leading to a dramatic decrease in SCW thickness of xylem fibers. Gene expression analyses showed that most of the structural genes involved in the biosynthesis of lignin, cellulose and xylans were significantly downregulated in MYB189-overexpressing poplars compared with the wild-type control. Chromatin immunoprecipitation-quantitative real-time polymerase chain reaction and transient expression assays revealed that MYB189 could directly bind to the promoters of secondary wall biosynthetic genes to repress their expression. Together, these data suggest that MYB189 acts as a repressor to regulate SCW biosynthesis in poplar.

Molecular mechanism of AtGA3OX1 and AtGA3OX2 genes affecting secondary wall thickening in stems in Arabidopsis

2013 ◽  
Vol 35 (5) ◽  
pp. 655-665 ◽  
Author(s):  
Zeng-Guang WANG ◽  
Guo-Hua CHAI ◽  
Zhi-Yao WANG ◽  
Xian-Feng TANG ◽  
Chang-Jiang SUN ◽  
...  
Keyword(s):  
Molecular Mechanism ◽  
Secondary Wall ◽  
Wall Thickening ◽  
Secondary Wall Thickening

scholarly journals MYB Transcription Factors and Its Regulation in Secondary Cell Wall Formation and Lignin Biosynthesis during Xylem Development

2021 ◽  
Vol 22 (7) ◽  
pp. 3560
Author(s):  
Ruixue Xiao ◽  
Chong Zhang ◽  
Xiaorui Guo ◽  
Hui Li ◽  
Hai Lu
Keyword(s):  
Cell Wall ◽  
Transcription Factors ◽  
Secondary Wall ◽  
Secondary Cell Wall ◽  
Lignin Biosynthesis ◽  
Cell Wall Formation ◽  
Long Distance ◽  
Secondary Cell Wall Formation ◽  
Myb Transcription Factors ◽  
Wall Formation

The secondary wall is the main part of wood and is composed of cellulose, xylan, lignin, and small amounts of structural proteins and enzymes. Lignin molecules can interact directly or indirectly with cellulose, xylan and other polysaccharide molecules in the cell wall, increasing the mechanical strength and hydrophobicity of plant cells and tissues and facilitating the long-distance transportation of water in plants. MYBs (v-myb avian myeloblastosis viral oncogene homolog) belong to one of the largest superfamilies of transcription factors, the members of which regulate secondary cell-wall formation by promoting/inhibiting the biosynthesis of lignin, cellulose, and xylan. Among them, MYB46 and MYB83, which comprise the second layer of the main switch of secondary cell-wall biosynthesis, coordinate upstream and downstream secondary wall synthesis-related transcription factors. In addition, MYB transcription factors other than MYB46/83, as well as noncoding RNAs, hormones, and other factors, interact with one another to regulate the biosynthesis of the secondary wall. Here, we discuss the biosynthesis of secondary wall, classification and functions of MYB transcription factors and their regulation of lignin polymerization and secondary cell-wall formation during wood formation.

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