Receptor-like protein kinases (RLKs) are encoded by a divergent multigene family and their functions have been implicated in a wide range of signal transduction pathways. In this study, we examined the effect of salicylic acid (SA) on the expression of RLK genes in Arabidopsis thaliana. RNA gel blot analysis revealed that transcripts of RKC1 and a number of its homologs, whose translation products contain C-X8-C-X2-C motifs in the putative extracellular domain, accumulated to a higher level in response to SA treatment of plants. The chimeric fusion between the RKC1 5'-upstream region and the beta-glucuronidase (GUS) reporter gene reproduced the SA responsiveness in transgenic plants. In addition, some of RLK genes of the leucine-rich repeat (LRR) class and those of the S-domain class were also induced by SA. We found that the upstream regions of these SA-responsive RLK genes contain the TTGAC sequence, which has been suggested to be important for induced expression of many plant defense genes. These results suggest the involvement of a number of RLKs in SA-mediated defense responses.
In the present study, we cloned genomic fragments of five members of the EXGT gene family, EXGT-A1, EXGT-A3, EXGT-A4, XTR2, and XTR3, and examined their expression in the wild type and in a series of acl mutants. In wild-type plants, the EXGT-A3 gene showed higher expression in lower internodes (internodes between nodes bearing axillary shoots) than in upper and young internodes, in which EXGT-A1 was highly expressed. EXGT-A4 was preferentially expressed in roots and XTR3 in siliques. The XTR2 gene was constitutively expressed. In acl1, acl3, and acl4 mutants, which have a severe defect in leaf expansion as well as in internode elongation, the EXGT-A1 gene showed reduced levels of expression before bolting of plants. In contrast, XTR3 was increased in these mutant seedlings. Reduction of EXGT-A1 expression was also detected after bolting of all acl mutants except acl2, whose growth defect is restricted to lower internodes. These results suggest the involvement of each EXGT in different aspects of organ development.
Restriction landmark genome scanning (RLGS) is a high-speed genome analysis method to detect DNA polymorphism, and is suitable to develop useful DNA markers for cultivar-discrimination of agricultural plants. The mat-rush, Juncus effusus is a vegetatively propagated crop that has been cultivated for over 500 years in Japan as the material of "tatami-omote," a surface of Japanese conventional mats. In recent years, Japanese mat-rush cultivars are grown in foreign countries and reimported to Japan in violation of the Seeds and Seedlings Law, economically damaging domestic production. The largest problem of illegal mat-rush reimportation has been with cv. Hinomidori. We developed a cultivar-discrimination DNA marker of mat-rush using RLGS, and detected the RLGS spot markers that didn't exist specifically in Hinomidori. The spot marker can be used with the RLGS method to identify Hinomidori accurately among cultivars.
We have developed a genetic marker that can identify a registered variety of mat rush in Japan. A vegetatively propagated plant, mat rush is cultivated and used as the material for the surface layer of tatami mats in Japan. Because it has been difficult to detect DNA polymorphism among mat rush cultivars, we applied restriction landmark genome scanning (RLGS) to discriminate mat rush cultivars. RLGS is a genome analysis technique that can detect many DNA polymorphisms as spots separated by two-dimensional electrophoresis. By cloning the DNA of spots specific to the superior mat rush cultivar 'Hinomidori' detected by RLGS, we developed a sequence-tagged site (STS) marker for polymerase chain reaction (PCR) analyses. This STS marker makes it possible to distinguish 'Hinomidori' specifically from other mat rush cultivars. The strategy of developing the STS marker in this study is applicable to other vegetatively propagated plants that are characterized by difficult DNA polymorphism detection.
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