کاهش خسارت خشکسالی در گندم دیم

نقش تنظیمی هورمن اکسین در رشد                        دریافت فایل اصل مقاله شماره ٨                                                                                                                    این مقاله مناسب برای ارائه در دروس : بیو تکنولوژی  - باغبانی- بیو شیمی گیاهی- زنتیک- اصلاح نباتات میباشد        درجه کیفی مقاله ١ است        برای دریافت متن ترجمه مقاله با مدیریت تماس بگیرید                      Auxin-responsive gene expression: genes, promoters and regulatory   factors                                   Abstract   A molecular approach to investigate auxin signaling in plants has led to the identification of several classes of early/primary auxin response genes. Within the promoters of these genes,   cis  elements that confer auxin responsiveness referred to as auxin-response elements or AuxREs) have been defined, and a family of  trans-acting transcription factors (auxin-response factors or ARFs) that bind with specificity to AuxREs has been characterized. A family of auxin regulated proteins referred to as Aux/IAA proteins also play a key role in regulating these auxinresponse genes. Auxin may regulate transcription on early response genes by influencing the types of interactions between ARFs and Aux/IAAs.                      بقیه متن در ادامه مطلب                                    این متن ناقص است متن کامل را دانلود کنید                                                                      Introduction       Auxins play a critical role in most major growth   responses throughout the development of a plant. Auxins   are thought to regulate or influence diverse responses   on a whole-plant level, such as tropisms, apical   dominance and root initiation, and responses on a   cellular level, such as cell extension, division and differentiation.   Over the past 20 years, it has been clearly   demonstrated that auxins can also exert rapid and specific   effects on genes at the molecular level. Numerous   sequences that are up-regulated or down-regulated by   auxin have been described (for reviews, see Abel   and Theologis, 1996; Sitbon and Perrot-Rechenmann,   1997; Guilfoyle, 1999). Research efforts in a number   of labs are currently focused on characterizing   the mechanisms involved in the regulation of genes   by auxin. The genes that have been most extensively   studied are those that are specifically induced by active   auxins within minutes of exposure to the hormone,   and are induced by auxin in the absence of protein   synthesis. These genes are referred to as early, or primary   auxin response genes, and fall into three major   classes (   Aux/IAAs, SAURs and GH3   s). In this review,   we will briefly discuss the early/primary auxin response   gene families, the TGTCTC-containing auxin   response promoter elements and the auxin response   factor (ARF) family of transcription factors. A number   of reviews that cover these areas in more detail   have been published (Guilfoyle, 1999; Guilfoyle   et al.   ,   1998a, b). This review will expand on these areas and   focus on information that has recently emerged (for   example, information derived from the publication of   the genome sequence of   Arabidopsis   ) or has recently   been published. We also present a working model for   the regulation of auxin response genes, based on the   current available information.       Auxin-responsive genes               genes have been identified in several laboratories           differential hybridization with probes from untreated   and auxin-treated hypocotyls or epicotyls (Walker and   Key, 1982; Hagen et al., 1984; Theologis et al., 1985).   The original Aux/IAA genes to be described (soybean           GmAux22 , GmAux28, GH1 and pea PS-IAA4/5 and   PS-IAA6 ) were expressed to moderate levels in elongating     regions of etiolated hypocotyls or epicotyls.   When these elongating regions are excised and incubated   in auxin-freemedium, the Aux/IAA mRNAs are   rapidly depleted, and can be rapidly induced by addition   of auxin to the medium. Aux/IAA mRNAs are   specifically induced by active auxins; protein synthesis   inhibitors, such as cycloheximide, also induce the   accumulation of Aux/IAA transcripts (for review, see   Guilfoyle, 1999).       Aux/IAA genes are present as multigene families     in soybean (Ainley et al., 1988), pea (Oeller et al.,   1993), mung bean (Yamamoto et al., 1992), tobacco   (Dargeviciute et al., 1998) and tomato (Nebenfuhr et   al   (see article by Liscum and Reed, 2002). Most of the       Arabidopsis genes are induced by auxin and show a     range of induction kinetics (Abel et al., 1995); however,       IAA 28 is not responsive to exogenous auxin     (Rogg et al., 2001). Aux/IAA genes are also found   in monocots and gymnosperms (GenBank EST database),   but are not found in organisms other than   plants.   Aux/IAA proteins generally range in size from   20 to 35 kDa. They are short-lived and localize to   the nucleus (Abel et al., 1994; Abel and Theologis,   1995). Four conserved motifs are found in most   Aux/IAA proteins, and these are referred to as domains   I, II, III and IV (Figure 1; Ainley et al., 1988;   Abel et al., 1995). Domain II plays a role in destabilizing   Aux/IAA proteins, and may be a target for   ubiquitination (Worley et al., 2000; Colon-Carmona       et al. , 2000; Ouellet et al., 2001). Domain III is     part of a motif that is predicted to resemble the amphipathic       βαα -fold found in the β-ribbon multimerization     and DNA-binding domains of Arc and MetJ   repressor proteins (Abel et al., 1994). The predicted       βαα motif has been shown to play a role in dimerization/     multimerization of Aux/IAA proteins and in   heterodimerization between Aux/IAA and ARF proteins   (Kim et al., 1997;Ulmasov et al., 1997b; Morgan       et al. , 1999; Ouellet et al., 2001); however, a role     for this motif in DNA binding has not been demonstrated.   The function of domains I and IV in Aux/IAA   proteins is not clear, but recent experiments suggest   that domain I may play a role in homodimerization of   Aux/IAA proteins (Ouellet et al., 2001).   A number of mutations in Aux/IAA genes have   been identified that provide insight into the role played   by these proteins in auxin responses. Some of these   mutants display light-grown phenotypes when grown   in the dark, suggesting that they bypass a requirement   for phytochrome in selected aspects of photomorphogenesis.   In this regard, recent studies have shown that   phytochrome A interacts with and phosphorylates the   amino-terminal half (encompassing domains I and II)   of selected Aux/IAA proteins in vitro (Colon-Carmona       et al. , 2000). The Aux/IAA mutants are discussed in     more detail in the article by Liscum and Reed in this   issue.     SAUR genes             A group of small, auxin-induced RNAs, referred to as   SAURs, was identified in a differential hybridization   screen of clones from auxin-treated soybean elongating   hypocotyl sections (McClure and Guilfoyle,   1987). These RNAs are induced within 2-5 min of   exposure to exogenous auxin. SAURs are moderately   abundant in the zone of cell elongation in soybean   hypocotyls, and most strongly expressed in epidermal   and cortical cells; induction by auxin results in   an elevation of transcripts within the same cell types   (Gee et al., 1991). Auxin induction of soybean SAURs   is transcriptionally regulated (McClure et al., 1989)   and specific for active auxins (McClure and Guilfoyle,   1987). Treatment with the protein synthesis inhibitor   cycloheximide (CHX) does not inhibit or enhance   auxin-induced transcriptional activation of soybean   SAURs, but does result in an increase in the abundance   of SAUR transcripts (McClure and Guilfoyle, 1987).   This induction by CHX was shown, however, not to         be at the level of transcription, and must result from   the stabilization of SAUR transcripts (Franco et al.,   1990).   Sequence analysis of three soybean SAUR cDNAs   and genes revealed that the genes contain no introns   (McClure et al., 1989). The deduced open reading   frames (ORF) encode proteins of 9-10 kDa. Five soybean       SAUR genes are clustered in a single 7 kb locus     of the nuclear genome, and each gene is oriented in   an opposing orientation. The 5 ORFs show a high   degree of homology, particularly in the C-terminal   portion of the protein. Database searches indicate that   the predicted structures of SAUR proteins are not   highly homologous to any other published amino acid   sequences.   Auxin-inducible SAURs have also been described   from mung bean (Yamamoto et al., 1992), pea (Guilfoyle       et al. , 1993), Arabidopsis (Gil et al., 1994),     radish (Anai et al., 1998) and Zea mays (Yang and   Poovaiah, 2000). In addition to auxin, some of these   SAUR mRNAs are induced by CHX (Gil et al., 1994).   In contrast to the soybean SAURs, the Arabidopsis       SAUR-AC1 appears to be transcriptionally induced by   CHX (Gil et al., 1994); SAUR-AC1 is also induced   by the plant hormone cytokinin (Timpte et al., 1995).   There are over 70 SAUR genes in Arabidopsis (Table   1). With one exception (AtSAUR11), all genes appear   to lack introns (GenBank annotations for AtSAUR26,   -33, -39   suspect that these annotations are incorrect and that   these genes consist of single exons, because the annotated   3' exons are unrelated to conserved SAUR       sequences). Many of the SAUR genes in Arabidopsis       are found in clusters, like those originally identified in   soybean. Clusters of eight, five, six and seven, and five       SAUR genes are found on chromosomes 1, 3, 4 and     5, respectively (Figure 2). It is not known how many   genes in this large gene family are expressed and are   auxin-inducible.   As mentioned above, at least some SAUR genes   are transcriptionally regulated by active auxins. There   is evidence, however, that SAURs are also regulated   post-transcriptionally. SAURs encode unstable mRNAs   (McClure and Guilfoyle, 1989; Franco et al.,   1990), and their high turnover rate may be due, in part,   to a conserved element (DST) in the 3 -untranslated   region of the mRNA (McClure et al., 1989; Newman           et al. , 1993) and/or elements within the ORF (Li   et al. , 1994). SAUR proteins may also be regulated     posttranslationally. Based on studies using anti-SAUR   antibodies, there is evidence that SAUR protein abun-           Figure 2. Chromosome positions of SAUR genes in Arabidopsis.   SAUR genes are indicated in boxes along with the BAC clone on     which they are found. Gray boxes above chromosomes 1 and 4   indicate that the chromosome position has not been determined.   See Table 1 for SAUR gene nomenclature and GenBank Gen Info   Identifier Number (Gene ID).   dance is low (Guilfoyle, 1999), suggesting that SAUR   protein half-life may be very short.   The function of SAUR proteins is still unknown;   however, they may play some role in an auxin signal   transduction pathway that involves calcium and   calmodulin. This possible role is suggested from recent   experiments that demonstrate in vitro binding   of calmodulin to an amino terminal domain in several   SAUR proteins (i.e., maize ZmSAUR1, soybean   SAUR 10A5 and Arabidopsis SAUR-AC1; Yang and   Poovaiah, 2000). While the amino terminus is not   highly conserved in amino acid sequence among the   SAUR proteins, a putative basic α-amphipathic helix   domain found in the amino terminus may provide a   calmodulin-binding site in these proteins.     GH3 genes             The GH3 mRNA is one of several sequences that   was recovered in a differential hybridization screen of   auxin-induced cDNA sequences derived from auxintreated,   etiolated soybean seedlings                                                                                                             Auxin-responsive promoters, promoter elements   and interacting factors   The promoters of several auxin-responsive genes (soybean     GH3       , soybean SAUR15A and pea PS-IAA4/5   )   have been analyzed in some detail, using a variety   of methods (e.g. deletion analysis, linker-scanning,   site directed mutagenesis, gain of function analysis;   reviewed by Guilfoyle, 1999). The smallest element   to be identified as auxin-responsive is a six-base pair   sequence, TGTCTC (Ulmasov   et al.   , 1997a, b). This   element has been shown to function in both composite   and simple auxin-response elements (AuxREs; Figure   3). In composite AuxREs, such as those found   in the GH3 promoter fragments D1 and D4, the   TGTCTC element is only functional if combined with   a coupling or constitutive element (Figure 3; reviewed   by Guilfoyle   et al.   , 1998a; Guilfoyle, 1999). Simple   AuxREs, derived from the alteration of naturally   occurring AuxREs, may function in the absence of   a coupling element if the TGTCTC elements occur   as direct or palindromic repeats that are appropriately   spaced (Figure 3; P3 (4X)-palindromic repeats   spaced by 3 bp; ER7-everted repeats spaced by 7 bp;   DR5-direct repeats spaced by 5 bp; DR5R-direct repeats   in the inverse orientation; reviewed by Guilfoyle     et al.         , 1998a; Guilfoyle, 1999). These simple, synthetic   AuxREs are 5-10 times more auxin-responsive   than natural AuxREs (Guilfoyle, 1999).   Natural AuxRE promoter-reporter constructs have   been used to study organ and tissue expression patterns   of auxin-responsive genes (Guilfoyle, 1999). These   constructs have been valuable tools to follow gene   expression events during growth responses associated   with changes in auxin gradients or sensitivities, such   as gravitropismand phototropism(Li   et al.   , 1999), and   in studies of signal transduction pathways in plants   (Kovtun   et al., 1998; Kovtun et al.   , 2000). Synthetic   AuxRE-reporter genes have been shown to respond to   auxin in a wide variety of organs, tissues and cell types   (Ulmasov   et al., 1997b; Oono et al.   , 1998). These   synthetic AuxREs, when fused to minimal promoterreporter   genes, have been used to monitor cell and/or   tissue responses to endogenous auxin in wild type   and mutant plants carrying the reporter gene (Sabatini     et al.       , 1999; Mockaitis and Howell, 2000; Zhao et al.   ,   2001). In addition, these constructs have provided the   basis to develop genetic screens for auxin response   mutants (Oono   et al., 1998; Murfett et al.   , 2001).   To identify proteins that bind to the TGTCTC element,   Ulmasov   et al.   (1997) used the synthetic AuxRE   P3 (4X) (see Figure 3) as a bait in a yeast one-hybrid   screen of an   Arabidopsis   cDNA expression library.   A novel transcription factor, referred to as auxinresponse   actor 1 or ARF1, was identified and shown to   bind with specificity to TGTCTC AuxREs.   Arabidopsis       has 23   ARF   -related genes (Table 3). One of these   genes (ARF23)         منبع:     www.ake.blogfa.com     منبع:     www.ake.blogfa.com     منبع:     www.ake.blogfa.com