In rice, all except OsMKK10-1 and OsMKK10-3 are expressed in four reproductive stages from the microarray **data** (Additional file 19). Moreover, all maize and poplar MKK genes are expressed in different tissues (Additional file 19). However, the transcriptional levels in PtMKKs have a great difference, while maize is not obvious (Additional file 19). To further validate the transcripts of B. distachyon MKK genes in different tissues, we tested five different tissues that were a part of Bd21 seedling, root, leaf, stem and young caryopsis, to analyze the tissue specific expression patterns of MKK genes (Additional file 20). The results revealed that all except BdMKK10-4 are expressed in five different tissues and BdMKK6 and BdMKK10-2 have higher transcriptional levels in young caryopsis than other tissues (Additional file 20). It is interesting that previous study show that MKK10 may not be biologically functional on account of the lack part of the phosphorylation site, but OsMKK10-2 can mediate the response to pathogen defense. Not as expected, MPK6 can be phosphorylated by OsMKK10-2 which have the kinase activity [28]. Moreover, we surveyed the gene expression of MKK under abiotic stresses that public microarray **data** of Arabidopsis under wound, drought, genotoxic, cold, osmotic, high-salinity, heat, oxidative and UV-B treatment were collected (Fig. 6d). Many plant MKK genes are up-regulated upon UV-B treatment, including AtMKK4 and AtMKK5. These results indicated that plant MKK genes may be involved in UV-B related signaling. To validate the expression profile of plant MKK genes in UV-B signaling, we performed the RT-qPCR experiments on RNA collected from different time points of B. distachyon plants under UV-B treatments. The results revealed that many MKK genes are up-regulated upon UV-B treatment, including BdMKK4 and BdMKK10-5, especially BdMKK10-5 originally have low-level transcripts in B. distachyon tissue (Additional file 20). These results indicated that BdMKK genes maybe also respond the UV-B stress. In a word, we can speculate that plant MKK genes play potential roles in UV-B related signaling.