PMC:1574314 / 19573-23629 JSONTXT

{"target":"https://pubannotation.org/docs/sourcedb/PMC/sourceid/1574314","sourcedb":"PMC","sourceid":"1574314","source_url":"https://www.ncbi.nlm.nih.gov/pmc/1574314","text":"MAPKs\n\nGroup A MPKs\nThe most extensively studied plant MAPKs belong to Group A which, in Arabidopsis, consists of three members, AtMPK3, AtMPK6 and AtMPK10 [4]. No direct putative ortholog of AtMPK10 has been detected in the poplar genome, but phylogenetic analysis [39] revealed the presence of two closely-related poplar presumed orthologs for the defense-related genes AtMPK3 (PtMPK3-1 and 3-2) and AtMPK6 (PtMPK6-1 and 6-2). In most organs, the expression of both PtMPK3-1 and 3-2 is lower than that of PtMPK6-1 and 6-2 (Figure 9; see additional file 2). PtMPK3-1 is relatively strongly expressed in roots and xylem, in comparison to other samples. In most organs PtMPK3-1 tends to be slightly more expressed than PtMPK3-2. However, this pattern is reversed in the four types of buds (male and female floral buds, lateral and terminal foliar buds) as well as in both types of catkins. PtMPK6-1 and 6-2 both show similar expression profiles across many organs, but TA for PtMPK6-1 becomes slightly more pronounced than that of its paralog in all four types of buds, in both types of catkins and in suspension-cultured cells.\n\nGroup B MPKs\nThere is less information on the biological roles of the other MAPK groups in plants, although some reports have suggested the potential involvement of group B MPK genes in response to environmental stresses as well as in cell development [4]. In poplar, PtMPK11 and PtMPK5-2, the most highly expressed of the four group B MAPK genes, are particularly actively transcribed in male and female floral buds (Figure 9). By contrast, the paralogous PtMPK5-1 gene shows the lowest level of TA within this group.\n\nGroup C MPKs\nAmong the group C MPKs, it has been reported that the tobacco Ntf3 gene is expressed in pollen [43] and that the Arabidopsis AtMPK7 gene has circadian rhythm-regulated patterns of expression [44]. The most highly expressed of the four poplar group C MPK genes is PtMPK7, with elevated TA levels detected in female catkin, buds, phloem, xylem, mature leaves (LPI 12) and roots (Figure 9). This gene is also differentially expressed in particular developmental stages of specific organs, with more abundant transcripts detected in floral buds (male and female) than in either type of catkin. A similar situation is observed for leaves, where PtMPK7 TA is more pronounced in mature leaves than in young leaves. This is similar to what has been reported for the rice putative ortholog OsMAPK4 (now annotated as OsMPK7 [39]), whose expression is higher in mature leaves than in young leaves [45].\n\nGroup D MPKs\nThe group D MPKs represent the largest group of MPKs in poplar, as they do in Arabidopsis and rice [4,39]. In rice and alfalfa (Medicago sativa), two group D MAPK genes (OsBMWK1 and MsTDY1) are induced transcriptionally by pathogen challenge and wounding, respectively [36,46] Activated OsBMWK1 (now annotated as OsMPK17-1 [39]) has also been shown to phosphorylate a transcription factor that binds a cis-acting element in the promoter of defence-related genes [47].\nIn poplar, PtMPK17 is the most highly expressed of the group D MPK genes and, indeed, it is the most highly expressed among all the MPK and MKK genes (Figure 9). On the other hand, the most weakly expressed group D MPK genes, PtMPK9-1 and PtMPK9-2, display low transcript levels in all organs with the noteworthy exception of all types of buds, and cell suspensions. As previously observed in other MPK groups, some members of the group D MPK genes seem to represent the paralogous products of recent genomic duplication events, since they possess a very high degree of sequence similarity, are located on different chromosomes and have only one direct putative ortholog in Arabidopsis [39]. PtMPK16-1 and PtMPK16-2 are particularly interesting paralogs, since they have very similar expression profiles in most organs, including male and female catkins. On the other hand, PtMPK16-1 is strongly expressed in male and female floral buds, whereas expression of PtMPK16-2 is barely detectable in these reproductive organs.","divisions":[{"label":"title","span":{"begin":0,"end":5}},{"label":"sec","span":{"begin":7,"end":1127}},{"label":"title","span":{"begin":7,"end":19}},{"label":"p","span":{"begin":20,"end":1127}},{"label":"sec","span":{"begin":1129,"end":1647}},{"label":"title","span":{"begin":1129,"end":1141}},{"label":"p","span":{"begin":1142,"end":1647}},{"label":"sec","span":{"begin":1649,"end":2553}},{"label":"title","span":{"begin":1649,"end":1661}},{"label":"p","span":{"begin":1662,"end":2553}},{"label":"title","span":{"begin":2555,"end":2567}},{"label":"p","span":{"begin":2568,"end":3035}}],"tracks":[]}