Photomorphogenesis is an essential program in plant development. This process is effected by the balanced cooperation of many factors under light and dark conditions. In a previous study, we showed ...that MYB hypocotyl elongation‐related (MYBH) is involved in cell elongation. To expand our understanding of MYBH function, we performed a yeast two‐hybrid assay and identified an MYB‐like Domain transcription factor (MYBD). In this study, we investigated the function of MYBD, which is an MYBH homolog involved in anthocyanin accumulation. MYBD expression increased in response to light or cytokinin, and MYBD enhanced anthocyanin biosynthesis via repression of MYBL2, which encodes a transcription factor that has a negative effect on this process. In addition, MYBD binding in vivo to the MYBL2 promoter and the lower level of histone H3K9 acetylation at the upstream region of MYBL2 in MYBD over‐expressing plants in comparison with wild‐type plants imply that MYBD represses MYBL2 expression via an epigenetic mechanism. HY5 directly binds to the MYBD promoter, which indicates that MYBD acts on HY5‐downstream in light‐ or cytokinin‐triggered signaling pathways, leading to anthocyanin accumulation. Our results suggest that, although MYBD and MYBH are homologs, they act in opposite ways during plant photomorphogenesis, and these functions should be examined in further studies.
Key message
The ectopic expression of
AtDFR
results in increased accumulation of anthocyanins leading to enhanced salinity and drought stress tolerance in
B
.
napus
plants.
Flavonoids with ...antioxidant effects confer many additional benefits to plants. Evidence indicates that flavonoids, including anthocyanins, protect tissues against oxidative stress from various abiotic stressors. We determined whether increases in anthocyanins increased abiotic stress tolerance in
Brassica napus
, because the values of
B
.
napus
L. and its cultivation area are increasing worldwide. We overexpressed
Arabidopsis
dihydroflavonol-4-reductase (
DFR
) in
B
.
napus
. Increased DFR transcript levels for
AtDFR
-
OX B
. shoots correlated with higher anthocyanin accumulation.
AtDFR
-
OX
Brassica shoots exhibited lower reactive oxygen species (ROS) accumulation than wild-type (WT) shoots under high NaCl and mannitol concentrations. This was corroborated by 3,3-diaminobenzidine staining for ROS scavenging activity in 1,1-diphenyl-2-picryl-hydrazyl assays. Shoots of the
AtDFR
-
OX B
.
napus
lines grown in a high salt medium exhibited enhanced salt tolerance and higher chlorophyll content than similarly grown WT plants. Our observations suggested that the
AtDFR
gene can be effectively manipulated to modulate salinity and drought stress tolerance by directing to high accumulation of anthocyanins in oilseed plants.
SUMMARY
Plants cannot fix nitrogen directly; they must absorb it from the soil through their roots, or in rare cases, form associations with nitrogen‐fixing bacteria. The efficiency of nitrogen use ...in most domesticated crops is low, and more than half of the available nitrogen in the soil can leach into the environment. Understanding the nitrogen signaling pathways is essential for maximizing the efficiency of nitrogen use in crops. In the present study, we characterized the Myeloblastosis (Myb)‐like gene NITROGEN RESPONSE DEFICIENCY 1 (NID1). We observed that the growth performance of nid1 knockout (KO) mutant Arabidopsis plants was better than that of wild‐type Col‐0 plants under very low‐nitrate conditions, leading to improved growth performance in the nid1 KO plants. The results of chromatin immunoprecipitation and electrophoretic mobility shift assays indicated that NID1 binds to the promoter of the NITRATE TRANSPORTER (NRT)1.1 gene. Furthermore, nid1 KO plants exhibited similar growth performance to the nid1 KO/chl1‐5 (nrt1.1 KO) double mutant and chl1‐5 (nrt1.1 KO) plants in response to low‐nitrate conditions. We suggest that NID1 plays a crucial role as a transcription factor in optimizing plant growth by modulating the transcript abundance of the nitrate transceptor CHL1, leading to enhanced ABA accumulation in low‐nitrate conditions.
Significance Statement
NID1 plays a crucial role as a transcription factor in modulating plant growth by controlling the transcript abundance of the nitrate transporter CHL1 and the ABA biosynthesis genes in response to low‐nitrogen conditions.
Various Myb proteins have been shown to play crucial roles in plants, including primary and secondary metabolism, determination of cell fate and identity, regulation of development and involvement in ...responses to biotic and abiotic stresses. The 126 R2R3 Myb proteins (with two Myb repeats) have been found in Arabidopsis; however, the functions of most of these proteins remain to be fully elucidated. In the present study, we characterized the function of AtMyb7 using molecular biological and genetic analyses. We used qRT‐PCR to determine the levels of stress‐response gene transcripts in wild‐type and atmyb7 plants. We showed that Arabidopsis AtMyb7 plays a critical role in seed germination. Under abscisic acid (ABA) and high‐salt stress conditions, atmyb7 plants showed a lower germination rate than did wild‐type plants. Furthermore, AtMyb7 promoter:GUS seeds exhibited different expression patterns in response to variations in the seed imbibition period. AtMyb7 negatively controls the expression of the gene encoding bZIP transcription factor, ABI5, which is a key transcription factor in ABA signalling and serves as a crucial regulator of germination inhibition in Arabidopsis.
The Casein lytic proteinase/heat shock protein 100 (Clp/Hsp100) proteins are chaperones that act to remodel/disassemble protein complexes and/or aggregates using the energy of ATP. In plants, one of ...the best-studied proteins from this family is cytosolic ClpB1 (At1g74310), better known in Arabidopsis as AtHsp101, which is a heat shock protein required for acclimation to high temperatures. Three other ClpB homologues have been identified in the Arabidopsis genome (ClpB2, ClpB3 and ClpB4; At4g14670, At5g15450 and At2g25140). To define further the roles of these chaperones in plants we investigated their intracellular localization, evolutionary relationships, patterns of expression and the phenotypes of corresponding T-DNA insertion mutants. We first found that ClpB2 was misannotated; there is no functional ClpB/Hsp100 gene at this locus. By fusing the putative transit peptides of ClpB3 and ClpB4 with GFP, we showed that these proteins are targeted to the chloroplast and mitochondrion, respectively, and we therefore designated them as ClpB-p and ClpB-m. Phylogenetic analysis supports two major lineages of ClpB proteins in plants, an 'eukaryotic', cytosol/nuclear-localized group containing AtHsp101, and an organelle-localized lineage, containing both ClpB-p and ClpB-m. Although AtHsp101, ClpB-p and ClpB-m transcripts all accumulate dramatically at high temperatures, the T-DNA insertion mutants of ClpB-p and ClpB-m show no evidence of seedling heat stress phenotypes similar to those observed in AtHsp101 mutants. Strikingly, ClpB-p knockouts were seedling lethals, failing to accumulate chlorophyll or properly develop chloroplasts. Thus, in plants, the function of ClpB/Hsp100 proteins is not restricted to heat stress, but a specific member of the family provides housekeeping functions that are essential to chloroplast development.
In response to environmental challenges, plant cells activate several signaling pathways that trigger the expression of transcription factors.
Arabidopsis MYB60
was reported to be involved in ...stomatal regulation under drought conditions. Here, two splice variants of the
MYB60
gene are shown to play a crucial role in stomatal movement. This role was demonstrated by over-expressing each variant, resulting in enhanced sensitivity to water deficit stress. The
MYB60
splice variants, despite the fact that one of which lacks the first two exons encoding the first MYB DNA binding domain, both localize to the nucleus and promote guard cell deflation in response to water deficit. Moreover,
MYB60
expression is increased in response to a low level of ABA and decreased in response to high level of ABA. At initial stage of drought stress, the plant system may modulate the root growth behavior by regulating
MYB60
expression, thus promotes root growth for increased water uptake. In contrast, severe drought stress inhibits the expression of the
MYB60
gene, resulting in stomatal closure and root growth inhibition. Taken together, these data indicate that
MYB60
plays a dual role in abiotic stress responses in
Arabidopsis
through its involvement in stomatal regulation and root growth.
Plant genomes contain numerous genes encoding chitinase‐like (CTL) proteins, which have a similar protein structure to chitinase belonging to the glycoside hydrolase (GH) family but lack the ...chitinolytic activity to cleave the β‐1,4‐glycosidic bond in chitins, polymers of N‐acetylglucosamine. CTL1 mutations found in rice and Arabidopsis have caused pleiotropic developmental defects, including altered cell wall composition and decreased abiotic stress tolerance, likely due to reduced cellulose content. In this study, we identified suppressor of hot2 1 (suh1) as a genetic suppressor of the ctl1hot2‐1 mutation in Arabidopsis. The mutation in SUH1 restored almost all examined ctl1hot2‐1 defects to nearly wild‐type levels or at least partially. SUH1 encodes a Golgi‐located type II membrane protein with glycosyltransferase (GT) activity, and its mutations lead to a reduction in cellulose content and hypersensitivity to cellulose biosynthesis inhibitors, although to a lesser extent than ctl1hot2‐1 mutation. The SUH1 promoter fused with the GUS reporter gene exhibited GUS activity in interfascicular fibers and xylem in stems; meanwhile, the ctl1hot2‐1 mutation significantly increased this activity. Our findings provide genetic and molecular evidence that the antagonistic activities of CTL1 and SUH1 play an essential role in assembling the cell wall in Arabidopsis.
Salt stress constitutes a major form of abiotic stress in plants. Histone modification plays an important role in stress tolerance, with particular reference to salt stress resistance. In the current ...study, we found that HDA15 overexpression confers salt stress resistance to young seedling stages of transgenic plants. Furthermore, salt stress induces
overexpression. Transcription levels of stress-responsive genes were increased in transgenic plants overexpressing
(
).
, an abscisic acid (ABA) biosynthetic gene, which is highly upregulated in
transgenic plants, enhanced the accumulation of ABA, which promotes adaptation to salt stress. ABA homeostasis in
plants is maintained by the induction of CYP707As, which optimize endogenous ABA levels. Lastly, we found that the double-mutant
plants are sensitive to salt stress, indicating that interaction between HDA15 and ELONGATED HYPOCOTYL 5 (HY5) is crucial to salt stress tolerance shown by
plants. Thus, our findings indicate that
is crucial to salt stress tolerance in
.
Summary
Calnexin (CNX) and calreticulin (CRT) are homologous lectin chaperones in the endoplasmic reticulum (ER) that facilitate glycoprotein folding and retain folding intermediates to prevent their ...transit via the secretary pathway. The Arabidopsis genome has two CNX (CNX1 and CNX2) and three CRT (CRT1, CRT2 and CRT3) homologs. Despite growing evidence of the biological roles of CNXs and CRTs, little is understood about their function in Arabidopsis growth and development under normal conditions. Here, we report that the deletion of CNX1, but not of CNX2, in the crt1 crt2 crt3 triple mutation background had an adverse effect on pollen viability and pollen tube growth, leading to a significant reduction in fertility. The cnx1 crt1 crt2 crt3 quadruple mutation also conferred severe defects in growth and development, including a shortened primary root, increased root hair length and density, and reduced plant height. Disruption of all five members of the CNX/CRT family was revealed to be lethal. Finally, the abnormal phenotype of the cnx1 crt1 crt2 crt3 quadruple mutants was completely rescued by either the CNX1 or CNX2 cDNA under the control of the CNX1 promoter, suggesting functional redundancy between CNX1 and CNX2. Taken together, these results provide genetic evidence that CNX and CRT play essential and overlapping roles during vegetative growth and male gametophyte development in Arabidopsis.
Significance Statement
Calnexin (CNX) and calreticulin (CRT) are homologous lectin chaperones in the endoplasmic reticulum (ER) that facilitate glycoprotein folding and retain folding intermediates to prevent their transit via the secretory pathway. The role of the CNX/CRT cycle in growth and development under normal growth conditions is not well understood. Here we show that CNX and CRT play essential and overlapping roles during vegetative growth and male gametophyte development in Arabidopsis.
Nitrogen is one of the most important macro-nutrients for plant growth and crop productivity. The amount of synthetic nitrogen fertilizers supplied to crops has dramatically increased, leading to a ...notable rise in crop yields. However, excessive nitrogen use has an enormous negative impact on ecosystems and human health through the emission of intense greenhouse gases, such as nitric oxide derived from the nitrate (NO
3
–
) assimilation cascade. Additionally, owing to the development of extensive irrigation in agriculture, crops are known to suffer from high salt stress. The effect of excessive nitrogen fertilizer application has been studied in some crops, but the effect of high nitrate level and salt stress on plant stress tolerance has not been studied in detail. Therefore, in this study we aimed to study the effects of high concentrations of NO
3
–
on salt stress tolerance in
Arabidopsis
. In addition, since anthocyanin functions as a reactive oxygen species (ROS) scavenger under abiotic stress conditions, we investigated whether enhanced anthocyanin content helps
Arabidopsis
to withstand higher salt stress levels under high NO
3
–
concentrations by using
pap1-D/fls1ko
double mutant plants, which accumulate excessive amount of anthocyanin. We found that Col-0 plants are more sensitive to salt stress under high NO
3
–
concentrations. Although both the
pap1-D/fls1ko
and
fls1ko
plants accumulated higher anthocyanin levels and radical scavenging activities than Col-0 plants under both normal and salt stress conditions, the
fls1ko
plants exhibited much better growth than the
pap1-D/fls1ko
plants. It appears that the enhanced NR activities and transcript levels of
NIA1
and
NIA2
in
pap1-D/fls1ko
and
fls1ko
plants led to an increase in the synthesis of proteins and proline, which increases osmolytes against salt stress. Our results demonstrate that optimal levels of anthocyanin accumulation can enhance growth performance of plants under high NO
3
–
and salt stress conditions.
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