The phytohormones ethylene (ET) and jasmonate (JA) regulate plant development, growth, and defense responses; however, the molecular basis for their signaling crosstalk is unclear. Here, we show that ...JA‐ZIM‐domain (JAZ) proteins, which repress JA signaling, repress trichome initiation/branching and anthocyanin accumulation, and inhibit the transcriptional activity of the basic helix‐loop‐helix (bHLH)‐MYB members (GLABRA3 (GL3)‐GL1 and TRANSPARENT TESTA 8 (TT8)‐MYB75) of WD‐repeat/bHLH/MYB (WBM) complexes. The ET‐stabilized transcription factors ETHYLENE‐INSENSITIVE3 (EIN3) and EIN3‐LIKE1 (EIL1) were found to bind to several members of WBM complexes, including GL3, ENHANCER OF GLABRA3 (EGL3), TT8, GL1, MYB75, and TRANSPARENT TESTA GLABRA1 (TTG1). This binding repressed the transcriptional activity of the bHLH‐MYB proteins and inhibited anthocyanin accumulation, trichome formation, and defenses against insect herbivores while promoting root hair formation. Conversely, the JA‐activated bHLH members GL3, EGL3, and TT8 of WBM complexes were able to interact with and attenuate the transcriptional activity of EIN3/EIL1 at the HOOKLESS1 promoter, and their overexpression inhibited apical hook formation. Thus, this study demonstrates a molecular framework for signaling crosstalk between JA and ET in plant development, secondary metabolism, and defense responses.
EIN3 and EIL1, core transcription factors of the ethylene signaling pathway, and JAZ proteins, repressors of jasmonate signaling, target WD‐repeat/bHLH/MYB complexes, thereby creating a molecular framework for ethylene–jasmonate crosstalk during development, secondary metabolism, and plant defenses against insect herbivores.
Precise coordination between stamen and pistil development is essential to make a fertile flower. Mutations impairing stamen filament elongation, pollen maturation, or anther dehiscence will cause ...male sterility. Deficiency in plant hormone gibberellin (GA) causes male sterility due to accumulation of DELLA proteins, and GA triggers DELLA degradation to promote stamen development. Deficiency in plant hormone jasmonate (JA) also causes male sterility. However, little is known about the relationship between GA and JA in controlling stamen development. Here, we show that MYB21, MYB24, and MYB57 are GA-dependent stamen-enriched genes. Loss-of-function of two DELLAs RGA and RGL2 restores the expression of these three MYB genes together with restoration of stamen filament growth in GA-deficient plants. Genetic analysis showed that the myb21-t1 myb24-t1 myb57-t1 triple mutant confers a short stamen phenotype leading to male sterility. Further genetic and molecular studies demonstrate that GA suppresses DELLAs to mobilize the expression of the key JA biosynthesis gene DAD1, and this is consistent with the observation that the JA content in the young flower buds of the GA-deficient quadruple mutant ga1-3 gai-t6 rga-t2 rgl1-1 is much lower than that in the WT. We conclude that GA promotes JA biosynthesis to control the expression of MYB21, MYB24, and MYB57. Therefore, we have established a hierarchical relationship between GA and JA in that modulation of JA pathway by GA is one of the prerequisites for GA to regulate the normal stamen development in Arabidopsis.
The phytohormones jasmonates (JAs) regulate diverse aspects of plant growth and defense responses. The JA-ZIM domain (JAZ) family of repressors are targeted by the JA receptor Coronatine Insensitive ...1 for ubiquitination and subsequent degradation via the 26S proteasome. We previously investigated the functions of JAZs in JA responses by analyzing jaz mutants of the phylogenetic group I (jaz1/2/5/6), group II/III (jaz10/11/12), group IV/V (jaz3/4/7/9 and jaz3/4/7/8/9), and their high-order mutant jaz1/2/3/4/5/6/7/9/10/11/12. Here, we examined JA-regulated root growth, apical hook curvature, flowering time, and defense against the insect Spodoptera exigua in the intermediate jaz mutants jaz1/2/5/6/10/11/12, jaz1/2/3/4/5/6/7/9, and jaz3/4/7/8/9/10/11/12. This study shows that these jaz mutants differentially affect JA responses, suggesting the complexity of JA pathway in these multiple jaz mutants.
The phytohormone jasmonates (JAs) regulate various defense responses and diverse developmental processes including stamen development and fertility. Previous studies showed that JA induces CORONATINE ...INSENSITIVE 1-mediated degradation of JA ZIM-domain (JAZ) proteins, and activates the MYB transcription factors (such as MYB21 and MYB24) to regulate stamen development. In this study, we further uncover the mechanism underlying how MYB24 interacts with JAZs to control JA-regulated stamen development. We show that N-terminus of MYB21/24 interacts with 10 out of 12 JAZ proteins while both N-terminus and C-terminus of MYB24 are involved in dimerization of MYB21 and MYB24. Interestingly, male sterility of the JA-deficient mutant
can be rescued by suitable level of the
overexpression but not by excessive high level of
. Surprisingly, overexpression of
, but not
, could cause male sterility. These results provide new insights on MYB factors in JA-regulated stamen development.
heterotrimeric G proteins regulate diverse plant growth and defense processes by coupling to 7TM AtRGS1 proteins. Although G protein mutants display alterations in response to multiple plant ...hormones, the underlying mechanism by which G proteins participate in the regulation of hormone responses remains elusive. Here, we show that genetic disruption of Gα and Gβ subunits results in reduced sensitivity to JA treatment. Furthermore, using confocal microscopy, VA-TIRFM, and FRET-FLIM, we provide evidence that stimulation by JA induces phosphorylation- and C-terminus-dependent endocytosis of AtRGS1, which then promotes dissociation of AtRGS1 from AtGPA1. In addition, SPT analysis reveals that JA treatment affects the diffusion dynamics of AtRGS1 and AtRGS1-ΔCt. Taken together, these findings suggest that the JA signal activates heterotrimeric G proteins through the endocytosis of AtRGS1 and dissociation of AtRGS1 from AtGPA1, thus providing valuable insight into the mechanisms of how the G protein system perceives and transduces phytohormone signals.
Jasmonates (JAs) are a class of plant hormones, essential in plant development and defense. JA induces the interaction of the JA receptor Coronatine Insensitive 1 with jasmonate ZIM-domain (JAZ) ...proteins, and promotes subsequent JAZs degradation, leading to the release of downstream factors and activation of diverse plant development and defense processes. We recently revealed that the IIIe bHLH transcription factors MYC2, MYC3, MYC4 and MYC5 interact with the MYB transcription factors MYB21 and MYB24 to form the bHLH-MYB complex, and JAZs repress the bHLH-MYB complex to regulate JA-mediated stamen development. Here, we further discuss the different properties of the components of the bHLH-MYB complex in expression pattern and stamen regulation.
The class III homeodomain-leucine zipper (HD-Zip III) gene family plays important roles in plant growth and development, including regulation of apical embryo patterning, embryonic shoot meristem ...formation, leaf polarity, vascular development, and meristem function, with a particularly crucial function in leaf development. Although HD-Zip III members are highly conserved in land plants, previous studies, such as genetic analyses based on multiple mutants in
Arabidopsis
and other plants, suggest that various HD-Zip III family genes have evolved with distinct functions and pleiotropic effects on plant growth and development. In this study, we analyzed a HD-Zip III member,
OsHox33
, and demonstrated that it plays an important role in age-dependent leaf senescence in rice. We constructed two specific RNAi vectors derived from the 5′-end region and 3′-UTR of
OsHox33
to knockdown its expression. Transgenic plants harboring either RNAi construct displayed similar phenotypes of precocious leaf senescence symptoms, suggesting that knockdown of
OsHox33
accelerates leaf senescence in rice.
pOsHox33::GUS
fusion expression and RT-PCR revealed that
OsHox33
is highly expressed in young organs, especially in young meristems such as shoot apical meristems, intercalary meristems, and young callus. In addition, real-time PCR indicated that
OsHox33
was more highly expressed in young leaves than in old leaves. To further investigate
OsHox33
function, we analyzed chloroplast ultrastructure in different-aged leaves of RNAi plants, and found that
OsHox33
knockdown accelerated chloroplast degradation, which is consistent with RNAi phenotypes. Finally, real-time PCR studies showed that
OsHox33
can regulate the expression of
GS1
and
GS2
, two senescence-associated genes. Taken together, the work presented here provides new insights into the function of HD-Zip III members in plants.
Viruses can infect host plants to cause severe diseases and substantial agricultural loss, while plants have evolved RNA interference （RNAi） strategy to defend against viral infection. Despite ...enormous efforts, only a few host proteins in RNAi pathway were shown to mediate antiviral defense, including RNA-dependent RNA polymerase I （RDRI）, RDR6, DICER-LIKE 2 （DCL2） and DCL4. In this study, we carried out a genetic screen for antiviral factors of RNAi pathway in Arabidopsis rdr6 background via inoculation with a 2b- deficient Cucumber Mosaic Virus （CMV-△2b）. We identified a mutant susceptible to CMV-△2h, referred to as enhancer o ojrdr6 （enor） 3-1 rdr6, and found that ENOR3 encodes a functionally unknown protein with high homology to the mammalian Non Imprinted in Prader-Willi/Angelman （NIPA） magnesium transporters. ENOR3 inhibits accumulation of CMV-△2b and acts additively with RDR1, RDR6, DCL2 and DCL4 in antivira/ defense. These results uncover that ENOR3 is a key component in antiviral RNAi Dathwav, and provide new insights into antiviral immunity.
The phytohormone jasmonate (JA) plays essential roles in plant growth, development and defense. In response to the JA signal, the CORONATINE INSENSITIVE 1 (COI1)-based SCF complexes recruit JASMONATE ...ZIM-domain (JAZ) repressors for ubiquitination and degradation, and subsequently regulate their downstream signaling components essential for various JA responses. Tremendous progress has been made in understanding the JA signaling pathway and its crosstalk with other phytohormone pathways during the past two decades. Recent studies have revealed that a variety of positive and negative regulators act as targets of JAZs to control distinctive JA responses, and that JAZs and these regulators function as crucial interfaces to mediate synergy and antagonism between JA and other phytohormones. Owing to different regulatory players in JA perception and JA signaling, a fine-tuning of JA-dependent processes in plant growth, development and defense is achieved. In this review, we will summarize the latest progresses in JA signaling and its crosstalk with gibberellin and ethylene.
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