The transcription factor TaFDL2-1A functions in auxin metabolism mediated by abscisic acid to regulate shoot growth in wheat
Bingxin WangLing ZhouLiqun LiDanmei PangYanhong LeiHao-Dong QiBirong ChenMengnan GuoQinghong ZengYanzhou XieXuejun Li
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Abstract Genetic strategies can be effective in improving wheat (Triticum aestivum L.) drought stress tolerance, but accumulating evidence suggests that overexpressing drought-resistance genes, especially genes related to the abscisic acid (ABA) signaling pathway, can retard plant growth. We previously characterized the positive roles of the wheat bZIP transcription factor TaFD-Like2-1A (TaFDL2-1A) in drought stress tolerance and ABA biosynthesis and response, whereas a dwarfing shoot exhibited under normal conditions. This study determined the underlying mechanisms that allow TaFDL2-1A to affect shoot growth. Overexpressing TaFDL2-1A decreased cell length, cell width, leaf size, shoot length, and biomass in wheat. The results of RNA-seq showed that multiple differently expressed transcripts are enriched in the auxin signaling pathway. Further analysis indicated higher expression levels of Gretchen Hagen3 (GH3) genes and lower indole-3-acetic acid (IAA) concentrations in the TaFDL2-1A overexpression lines. Exogenous IAA treatment restored the phenotypes of the TaFDL2-1A overexpression lines to wild-type levels. Transcriptional regulation analysis suggested that TaFDL2-1A enhances the expression of auxin metabolism genes, such as TaGH3.2-3A, TaGH3.2-3B, TaGH3.8-2A, and TaGH3.8-2D, by directly binding to ACGT core cis-elements. Furthermore, tafdl2 knock-out plants had lower expression levels of these GH3 genes and higher IAA levels than Fielder wheat. These GH3 gene expression and IAA levels were induced and reduced in Fielder wheat and tafdl2 knock-out plants treated with exogenous ABA. Our findings elucidate mechanisms underlying the functional redundancy of TaFDL2-1A in the crosstalk between ABA and IAA to affect shoot growth and provide insights into the balance between drought resistance and yield in wheat.Keywords:
Dwarfing
Crosstalk
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【Objective】Since the “green revolution” in the middle 20th century,in which wheat breeding was focused on dwarfing,wheat breeding in various countries of the world has been confined to a limited number of recessive dwarfing sources such as Rht1,Rht2 and Rht8. This study is intended to broaden the dwarfing sources of wheat so as to help the development of highly intensive varieties in wheat cultivation. 【Method】 Five known dominant dwarfing source genes(Rht3,Rht10,Rht12,Rht21 and Olesen) and 7 dominant dwarfing sources with moderate dwarfing ability developed and selected by the Wheat Breeding Laboratory of Southwest University (China),were incorporated into 4 mediums or tall-statured wheat varieties (F1B4 recurrent paternal parents) through back-crossing,thus establishing 4 sets of near isogenic lines of dwarfing genes. In 2005-2006,a multi-factor comparative experiment was conducted under non-competitive conditions of these near isogenic lines to investigate the effects of the genetic backgrounds of the drawfing genes and the recurrent paternal parents on the major agronomic characters. 【Result】 Under the unified genetic backgrounds of the present study,the plant height of all the 12 dwarfing sources ranged from 37.9～74.3cm,being in a significant correlation with their grain weight per plant (r=0.8884). Their grain weight per plant increased by 0.24 g as plant height increased by 1 cm. The agronomic characters of the NILs improved rapidly as their plant height increased and their dwarfing effect weakened. The productivity of a dwarfing source variety approached or exceeded its medium or tall-statured recurrent parent whenits plant height was raised to 60 cm or more. It,therefore,is possible to use such innovative dwarfing sources directly in hybridization breeding of wheat. In addition to such major effects,the 12 dwarfing genes showed pleiotropic effects of delaying the heading of the paternal recurrent parents and reducing their 1000-seed-weight,which,however,can be overcome by modifying the genetic backgrounds of the recurrent paternal parent. The experiment provides additional evidence that dwarfing source varieties with a plant height of 50 cm or less,with their high dwarfing effect,can hardly be employed directly in wheat breading due to their low biomass production;however,their plant height can be increased,to different extents,and some weak dwarfing source varieties may have an ideal plant height of 70-80 cm. This can be conducted through mutation of the major dwarfing gene(s) or the modification by special genetic background.【Conclusion】 Strengthening the research of weak dwarfing sources with increased plant height is a fundamental approach in application of dominant dwarfing sources in wheat hybridization breeding. It is recommended that the dominant weak dwarfing sources developed and selected in this study,i.e. SW07,SW05,YD Ai,SW02 and Rht21be utilized in “gene-designed” dwarfing breeding of wheat.
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Abstract The interplay between abscisic acid (ABA) and salicylic acid (SA) influences plant responses to various (a)biotic stresses; however, the underlying mechanism(s) for this crosstalk is largely unknown. Here we report that type 2C protein phosphatases (PP2Cs), some of which are negative regulators of ABA signaling, bind SA. SA binding suppressed the ABA-enhanced interaction between these PP2Cs and various ABA receptors belonging to the PYR/PYL/RCAR protein family. Additionally, SA suppressed ABA-enhanced degradation of PP2Cs and ABA-induced stabilization of SnRK2s. Supporting SA’s role as a negative regulator of ABA signaling, exogenous SA suppressed ABA-induced gene expression, whereas SA-deficient sid2-1 mutants displayed heightened PP2C degradation and hypersensitivity to ABA-induced suppression of seed germination. Together, these results suggest a new molecular mechanism through which SA antagonizes ABA signaling. A better understanding of the crosstalk between these hormones is important for improving the sustainability of agriculture in the face of climate change.
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ABSTRACT Auxin and abscisic acid (ABA) modulate numerous aspects of plant development together, mostly in opposite directions, suggesting that extensive crosstalk occurs between the signalling pathways of the two hormones. However, little is known about the nature of this crosstalk. We demonstrate that ROP‐interactive CRIB motif‐containing protein 1 (RIC1) is involved in the interaction between auxin‐ and ABA‐regulated root growth and lateral root formation. RIC1 expression is highly induced by both hormones, and expressed in the roots of young seedlings. Whereas auxin‐responsive gene induction and the effect of auxin on root growth and lateral root formation were suppressed in the ric1 knockout, ABA‐responsive gene induction and the effect of ABA on seed germination, root growth and lateral root formation were potentiated. Thus, RIC1 positively regulates auxin responses, but negatively regulates ABA responses. Together, our results suggest that RIC1 is a component of the intricate signalling network that underlies auxin and ABA crosstalk.
Crosstalk
Lateral root
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Excised embryonic bean axes (Phaseolus vulgaris, var. White Marrowfat) rapidly metabolize 2-(14)C-(+/-)-abscisic acid to two compounds, M-1 and M-2, which have very low growth-inhibitory activity. Chemical tests indicate the M-1 and M-2 are not previously described abscisic acid metabolites. M-2 accumulates in the axes and evidence is presented for the hypothesis that abscisic acid --> M-1 --> M-2. Zeatin, which partially reverses the abscisic acid-mediated growth inhibition of axes, neither decreases abscisic acid uptake nor causes any major changes in its metabolism. It was observed that axes transferred from abscisic acid-containing solutions to buffer resume control rates of fresh weight increase while still containing considerable quantities of abscisic acid.
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Tomato shoots that had been (a) fed (�)-[2H9]abscisic aldehyde via the xylem or (b) fed H218O together with (�)-[2H9]abscisic aldehyde via the xylem or (c) exposed to 18O2 and fed (�)-[2H9]abscisic aldehyde, were then wilted. The abscisic acid present was isolated, methylated and resolved into (+)- and (-)- methyl abscisate. These methyl abscisate samples were then examined by negative ion chemical ionisation (methane) gas chromatography/mass spectrometry. The undeuteriated (+)-abscisic acid contained no 180 from H218O but did contain one 18O from 18O2. No 18O from either of these sources was present in the undeuteriated (-)-abscisic acid. It was not possible to discount the xanthophyll hypothesis for the origin of stress-induced abscisic acid on the basis of these experiments. Both (+)- and (-)- multiply deuteriated abscisic acid contained one and two 18O atoms from H218O but none from 18O2. It is postulated that this multiply deuteriated (�)-abscisic acid is formed by a separate enzyme system from that which forms endogenous stress-induced (+)-abscisic acid. On the basis of the low incor- poration of abscisic aldehyde into abscisic acid, it is suggested that the endogenous precursor of stress- induced abscisic acid is an as yet unidentified structure and that abscisic aldehyde competes with it.
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The main activities of abscisic acid in seeds are abscisic acid synthesis,catabolism,transport and response.Abscisic acid levels,the specific enzyme and the transcription factor in signal transduction pathway of abscisic acid,the relation between abscisic acid and dormancy of seeds are reviewed in this paper.
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The interplay between abscisic acid (ABA) and salicylic acid (SA) influences plant responses to various (a)biotic stresses; however, the underlying mechanism for this crosstalk is largely unknown. Here, we report that type 2C protein phosphatases (PP2Cs), some of which are negative regulators of ABA signaling, bind SA. SA binding suppressed the ABA-enhanced interaction between these PP2Cs and various ABA receptors belonging to the PYR/PYL/RCAR protein family. Additionally, SA suppressed ABA-enhanced degradation of PP2Cs and ABA-induced stabilization of SnRK2s. Supporting SA's role as a negative regulator of ABA signaling, exogenous SA suppressed ABA-induced gene expression, whereas the SA-deficient sid2-1 mutant displayed heightened PP2C degradation and hypersensitivity to ABA-induced suppression of seed germination. Together, these results suggest a new molecular mechanism through which SA antagonizes ABA signaling. A better understanding of the crosstalk between these hormones is important for improving the sustainability of agriculture in the face of climate change.
Crosstalk
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The closure of stomata by abscisic acid was examined in several species of plants through measurements of CO(2) and H(2)O exchange by the leaf. The onset of closure was very rapid, beginning at 3 minutes from the time of abscisic acid application to the cut base of the leaf of corn, or at 8 or 9 minutes for bean, Rumex and sugarbeet; rose leaves were relatively slow at 32 minutes. The timing and the concentration of abscisic acid needed to cause closure were related to the amounts of endogenous abscisic acid in the leaf. Closure was obtained in bean leaves with 8.9 picomoles/cm(2). (+)-Abscisic acid had approximately twice the activity of the racemic material. The methyl ester of abscisic acid was inactive, and trans-abscisic acid was likewise inactive. The effects of stress on levels of endogenous abscisic acid, and the ability of very small amounts of abscisic acid to cause rapid closure suggests that stomatal control is a regulatory function of this hormone.
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