To clarify the involvement of the arginine decarboxylase (ADC) pathway in the salt stress response, the polyamine titre, putrescine biosynthetic gene expression, and enzyme activities were investigated in apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] in vitro callus under salt stress, during recovery after stress, and when ADC was inhibited by D-arginine, an inhibitor of ADC. Salt stress (200 mM NaCl) caused an increase in thiobarbituric acid-reactive substances (TBARS) and electrolyte leakage (EL) of the callus, which was accompanied by an increase in free putrescine content, during 7 d of treatment. Conjugated putrescine was also increased, but this increase was limited to the early stage of salt stress. Accumulation of putrescine was in accordance with induction of ADC activity and expression of the apple ADC gene (MdADC). When callus that had been treated with 200 mM NaCl was transferred to fresh medium with (successive stress) or without (recovery) NaCl, TBARS and EL were significantly reduced in the recovery treatment, indicating promotion of formation of new callus cells, compared with the successive stress treatment. Meanwhile, MdADC expression and ADC activity were also decreased in the callus undergoing recovery, whereas those of the callus under successive stress were increased. Ornithine decarboxylase (ODC) activity showed a pattern opposite to that of ADC in these conditions. D-Arginine treatment led to more serious growth impairment than no treatment under salt stress. In addition, accumulation of putrescine, induction of MdADC, and activation of ADC in D-arginine-treated callus were not comparable with those of the untreated callus. Exogenous addition of putrescine could alleviate salt stress in terms of fresh weight increase and EL. All of these findings indicated that the ADC pathway was tightly involved in the salt stress response. Accumulation of putrescine under salt stress, the possible physiological role of putrescine in alleviating stress damage, and involvement of MdADC and ADC in response to salt stress are discussed.
Radish (Raphanus sativus L., n = 9) is one of the major vegetables in Asia. Since the genomes of Brassica and related species including radish underwent genome rearrangement, it is quite difficult to perform functional analysis based on the reported genomic sequence of Brassica rapa. Therefore, we performed genome sequencing of radish. Short reads of genomic sequences of 191.1 Gb were obtained by next-generation sequencing (NGS) for a radish inbred line, and 76,592 scaffolds of ≥300 bp were constructed along with the bacterial artificial chromosome-end sequences. Finally, the whole draft genomic sequence of 402 Mb spanning 75.9% of the estimated genomic size and containing 61,572 predicted genes was obtained. Subsequently, 221 single nucleotide polymorphism markers and 768 PCR-RFLP markers were used together with the 746 markers produced in our previous study for the construction of a linkage map. The map was combined further with another radish linkage map constructed mainly with expressed sequence tag-simple sequence repeat markers into a high-density integrated map of 1,166 cM with 2,553 DNA markers. A total of 1,345 scaffolds were assigned to the linkage map, spanning 116.0 Mb. Bulked PCR products amplified by 2,880 primer pairs were sequenced by NGS, and SNPs in eight inbred lines were identified.
SummaryBrassica napus is an amphidiploid species with the A genome from Brassica rapa and the C genome from Brassica oleracea. Although B. rapa, B. oleracea and artificially synthesized amphidiploids with the AC genome are self-incompatible, B. napus is self-compatible. Six S genotypes were identified in B. napus, five of which had class I S haplotypes from one species and a class II S haplotype from the other species, and mutations causing self-compatibility were identified in three of these S genotypes. The most predominant S genotype (BnS-1;BnS-6), which is that of cv. 'Westar', had a class I S haplotype similar to B. rapa S-47 (BrS-47) and a class II S haplotype similar to B. oleracea S-15 (BoS-15). The stigmas of 'Westar' rejected the pollen grains of both BrS-47 and BoS-15, while reciprocal crossings were compatible. Insertion of a DNA fragment of about 3.6 kb was found in the promoter region of the SP11/SCR allele of BnS-1, and transcripts of SP11/SCR were not detected in 'Westar'. The nucleotide sequence of the SP11 genomic DNA of BnS-6 was 100% identical to that of SP11 of BoS-15. Class I SP11 alleles from one species showed dominance over class II SP11 alleles from the other species in artificially synthesized B. napus lines, suggesting that the non-functional dominant SP11 allele suppressed the expression of the recessive SP11 allele in 'Westar'. Two other S genotypes in B. napus also had non-functional class I S haplotypes together with recessive BnS-6. These observations suggest independent origins of self-compatibility in B. napus.
For identification of genes responsible for varietal differences in flowering time and leaf morphological traits, we constructed a linkage map of Brassica rapa DNA markers including 170 EST-based markers, 12 SSR markers, and 59 BAC sequence-based markers, of which 151 are single nucleotide polymorphism (SNP) markers. By BLASTN, 223 markers were shown to have homologous regions in Arabidopsis thaliana, and these homologous loci covered nearly the whole genome of A. thaliana. Synteny analysis between B. rapa and A. thaliana revealed 33 large syntenic regions. Three quantitative trait loci (QTLs) for flowering time were detected. BrFLC1 and BrFLC2 were linked to the QTLs for bolting time, budding time, and flowering time. Three SNPs in the promoter, which may be the cause of low expression of BrFLC2 in the early-flowering parental line, were identified. For leaf lobe depth and leaf hairiness, one major QTL corresponding to a syntenic region containing GIBBERELLIN 20 OXIDASE 3 and one major QTL containing BrGL1, respectively, were detected. Analysis of nucleotide sequences and expression of these genes suggested possible involvement of these genes in leaf morphological traits.
The self-incompatibility (SI) system of the Brassicaceae is based on allele-specific interactions among haplotypes of the S locus. In all tested self-incompatible Brassicaceae, the S haplotype encompasses two linked genes, one encoding the S-locus receptor kinase (SRK), a transmembrane kinase displayed at the surface of stigma epidermal cells, and the other encoding its ligand, the S-locus cysteine-rich (SCR) protein, which is localized in the pollen coat. Transfer of the two genes to self-fertile Arabidopsis thaliana allowed the establishment of robust SI in several accessions, indicating that the signaling cascade triggered by this receptor-ligand interaction and the resulting inhibition of "self" pollen by the stigma have been maintained in extant A. thaliana. Based on studies in Brassica species, the membrane-tethered kinase MLPK, the ARM repeatcontaining U-box protein ARC1, and the exocyst subunit Exo70A1 have been proposed to function as components of an SI signaling cascade. Here we tested the role of these molecules in the SI response of A. thaliana SRK-SCR plants. We show that the A. thaliana ARC1 ortholog is a highly decayed pseudogene. We also show that, unlike reports in Brassica, inactivation of the MLPK ortholog AtAPK1b and overexpression of Exo70A1 neither abolish nor weaken SI in A. thaliana SRK-SCR plants. These results do not support a role for these molecules in the SI response of A. thaliana.receptor signaling | S locus receptor kinase
Arginine decarboxylase (ADC) and ornithine decarboxylase (ODC) are two important enzymes responsible for putrescine biosynthesis. In this study, a full-length ADC cDNA (MdADC) was isolated from apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.]. Meanwhile, a partial ODC (pMdODC) could be amplified only by a second RCR from the RT-PCR products, whereas a full-length ODC could not be obtained by either cDNA library screening or 5'- and 3'-RACEs, suggesting quite low expression. Moreover, D-arginine, an ADC inhibitor, caused a decrease in ADC activity and severely inhibited the growth of apple callus, which could be partially resumed by exogenous addition of putrescine, whereas alpha-difluoromethylornithine (DFMO), an inhibitor for ODC, caused the incomplete repression of callus growth without changing ODC activity. RNA gel blot showed that the expression level of MdADC was high in young tissues/organs with rapid cell division and was positively induced by chilling, salt, and dehydration, implying its involvement in both cell growth and these stress responses. By contrast, the transcript of ODC could not be detected by RNA gel blot analysis. Based on the present study, it is possible to conclude that (i) the ODC pathway is active in apple, although the expression level of the pMdODC gene homologous with its counterparts found in other plant species is quite low; and (ii) MdADC expression correlates with cell growth and stress responses to chilling, salt, and dehydration, suggesting that ADC is a primary biosynthetic pathway for putrescine biosynthesis in apple.
Most wild plants and some crops of the Brassicaceae express self-incompatibility, which is a mechanism that allows stigmas to recognize and discriminate against “self” pollen, thus preventing self-fertilization and inbreeding. Self-incompatibility in this family is controlled by a single S locus containing two multiallelic genes that encode the stigma-expressed S-locus receptor kinase and its pollen coat-localized ligand, the S-locus cysteine-rich protein. Physical interaction between receptor and ligand encoded in the same S locus activates the receptor and triggers a signaling cascade that results in inhibition of “self” pollen. Sequence information for many S-locus haplotypes in Brassica species has spurred studies of dominance relationships between S haplotypes and of S-locus structure, as well as the development of methods for S genotyping. Furthermore, molecular genetic studies have begun to identify genes that encode putative components of the self-incompatibility signaling pathway. In parallel, standard genetic analysis and QTL analysis of the poorly understood interspecific incompatibility phenomenon have been initiated to identify genes responsible for the inhibition of pollen from other species by the stigma. Herewith, we review recent studies of self-incompatibility and interspecific incompatibility, and we propose a model in which a universal pollen-inhibition pathway is shared by these two incompatibility systems.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.