Brassinosteroids (
Rhamnose is required in
- PAR ID:
- 10056271
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- The Plant Journal
- Volume:
- 94
- Issue:
- 4
- ISSN:
- 0960-7412
- Page Range / eLocation ID:
- p. 649-660
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract BRs ) are essential plant growth‐promoting hormones involved in many processes throughout plant development, from seed germination to flowering time. SinceBRs do not undergo long‐distance transport, cell‐ and tissue‐specific regulation of hormone levels involves both biosynthesis and inactivation. To date, tenBR ‐inactivating enzymes, with at least five distinct biochemical activities, have been experimentally identified in the model plantArabidopsis thaliana . Epigenetic interactions betweenT‐DNA insertion alleles and genetic linkage have hindered analysis of higher‐order null mutants in these genes. A previous study demonstrated that thebas1‐2 sob7‐1 ben1‐1 triple‐null mutant could not be characterized due to epigenetic interactions between the exonicT‐DNA insertions inbas1‐2 andsob7‐1, causing the intronicT‐DNA insertion ofben1‐1 to revert to a partial loss‐of‐function allele. We usedCRISPR‐Cas9 genome editing to avoid this problem and generated thebas1‐2 sob7‐1 ben1‐3 triple‐null mutant. This triple‐null mutant resulted in an additive seedling long‐hypocotyl phenotype. We also uncovered a role for ‐mediatedBEN1 BR ‐inactivation in seedling cotyledon petiole elongation that was not observed in the singleben1‐2 null mutant but only in the absence of both andBAS1 . In addition, genetic analysis demonstrated thatSOB7 does not contribute to the early‐flowering phenotype, whichBEN1 andBAS1 redundantly regulate. Our results show thatSOB7 ,BAS1 andBEN1 , have overlapping and independent roles based on their differential spatiotemporal tissue expression patternsSOB7 -
Summary Plants mount coordinated immune responses to defend themselves against pathogens. However, the cellular components required for plant immunity are not fully understood. The jasmonate‐mimicking coronatine (
COR ) toxin produced byPseudomonas syringae pv.tomato (Pst )DC 3000 functions to overcome plant immunity. We previously isolated eight Arabidopsis (scord ) mutants that exhibit increased susceptibility to aCOR ‐deficient mutant ofPst DC 3000. Among them, thescord6 mutant exhibits defects both in stomatal closure response and in restricting bacterial multiplication inside the apoplast. However, the identity of remained elusive.SCORD 6In this study, we aim to identify the
gene.SCORD 6We identified
via next‐generation sequencing and found it to beSCORD 6 (MURUS 1 ), which is involved in the biosynthesis ofMUR 1GDP ‐l ‐fucose.Discovery of
asSCORD 6 led to a series of experiments that revealed a multi‐faceted role ofMUR 1l ‐fucose biosynthesis in stomatal and apoplastic defenses as well as in pattern‐triggered immunity and effector‐triggered immunity, including glycosylation of pattern‐recognition receptors. Furthermore, compromised stomatal and/or apoplastic defenses were observed in mutants of several fucosyltransferases with specific substrates (e.g.O ‐glycan,N ‐glycan or theDELLA transcriptional repressors). Collectively, these results uncover a novel and broad role ofl ‐fucose and protein fucosylation in plant immunity. -
Summary Boron is a micronutrient that is required for the normal growth and development of vascular plants, but its precise functions remain a subject of debate. One established role for boron is in the cell wall where it forms a diester cross‐link between two monomers of the low‐abundance pectic polysaccharide rhamnogalacturonan‐
II (RG ‐II ). The inability ofRG ‐II to properly assemble into a dimer results in the formation of cell walls with abnormal biochemical and biomechanical properties and has a severe impact on plant productivity. Here we describe the effects onRG ‐II structure and cross‐linking and on the growth of plants in which the expression of aGDP ‐sugar transporter (GONST 3/GGLT 1) has been reduced. In the ‐silenced plants the amount of L‐galactose in side‐chain A ofGGLT 1RG ‐II is reduced by up to 50%. This leads to a reduction in the extent ofRG ‐II cross‐linking in the cell walls as well as a reduction in the stability of the dimer in the presence of calcium chelators. The silenced plants have a dwarf phenotype, which is rescued by growth in the presence of increased amounts of boric acid. Similar to themur1 mutant, which also disruptsRG ‐II cross‐linking, ‐silenced plants display a loss of cell wall integrity under salt stress. We conclude thatGGLT 1GGLT 1 is probably the primary GolgiGDP ‐L‐galactose transporter, and providesGDP ‐L‐galactose forRG ‐II biosynthesis. We propose that the L‐galactose residue is critical forRG ‐II dimerization and for the stability of the borate cross‐link. -
Summary Many plants require prolonged exposure to cold to acquire the competence to flower. The process by which cold exposure results in competence is known as vernalization. In
Arabidopsis thaliana , vernalization leads to the stable repression of the floral repressor via chromatin modification, including an increase of trimethylation on lysine 27 of histone H3 (H3K27me3) by Polycomb Repressive Complex 2 (FLOWERING LOCUS CPRC 2). Vernalization in pooids is associated with the stable induction of a floral promoter, (VERNALIZATION 1VRN1 ). From a screen for mutants with a reduced vernalization requirement in the model grassBrachypodium distachyon , we identified two recessive alleles of (ENHANCER OF ZESTE ‐LIKE 1 ).EZL 1 is orthologous toEZL 1A. thaliana , a gene that encodes the catalytic subunit ofCURLY LEAF 1PRC 2.B. distachyon ezl1 mutants flower rapidly without vernalization in long‐day (LD ) photoperiods; thus, is required for the proper maintenance of the vegetative state prior to vernalization. Transcriptomic studies inEZL 1ezl1 revealed mis‐regulation of thousands of genes, including ectopic expression of several floral homeotic genes in leaves. Loss of results in the global reduction of H3K27me3 and H3K27me2, consistent with this gene making a major contribution toEZL 1PRC 2 activity inB. distachyon . Furthermore, inezl1 mutants, the flowering genes andVRN 1 (AGAMOUS ) are ectopically expressed and have reduced H3K27me3. Artificial microAG RNA knock‐down of either orVRN 1 inAG ezl1‐1 mutants partially restores wild‐type flowering behavior in non‐vernalized plants, suggesting that ectopic expression inezl1 mutants may contribute to the rapid‐flowering phenotype. -
Abstract The sorting of eukaryotic proteins to various organellar destinations requires receptors that recognize cargo protein targeting signals and facilitate transport into the organelle. One such receptor is the peroxin
PEX 5, which recruits cytosolic cargo carrying a peroxisome‐targeting signal (PTS ) type 1 (PTS 1) for delivery into the peroxisomal lumen (matrix). In plants and mammals,PEX 5 is also indirectly required for peroxisomal import of proteins carrying aPTS 2 signal becausePEX 5 binds thePTS 2 receptor, bringing the associatedPTS 2 cargo to the peroxisome along withPTS 1 cargo. DespitePEX 5 being thePTS 1 cargo receptor, previously identified Arabidopsispex5 mutants display either impairment of bothPTS 1 andPTS 2 import or defects only inPTS 2 import. Here, we report the first Arabidopsispex5 mutant with an exclusivePTS 1 import defect. In addition to markedly diminishedGFP ‐PTS 1 import and decreased pex5‐2 protein accumulation, thispex5‐2 mutant shows typical peroxisome‐related defects, including inefficient β‐oxidation and reduced growth. Growth at reduced or elevated temperatures ameliorated or exacerbatedpex5‐2 peroxisome‐related defects, respectively, without markedly changing pex5‐2 protein levels. In contrast to the diminishedPTS 1 import,PTS 2 processing was only slightly impaired andPTS 2‐GFP import appeared normal inpex5‐2 . This finding suggests that even minor peroxisomal localization of thePTS 1 proteinDEG 15, thePTS 2‐processing protease, is sufficient to maintain robustPTS 2 processing.