Genome-Wide Identification of Sugar Beet (Beta vulgaris L.) MAPKKKs Gene Family and Their Expression in Response to Salt Stress

Mitogen-activated protein kinase kinase kinases (MAPKKKs) are pivotal components of mitogen-activated protein kinase (MAPK) cascades and play important roles in many biological processes. To explore the biological function and genes expression patterns of the MAPKKK gene family in sugar beet (Beta vulgaris L.), a systematic analysis of BvMAPKKK was conducted. In the current study, a total of 40 BvMAPKKK genes are identified in the genome of sugar beet and can be categorized into three groups, ZIK, MEKK, and Raf with 9, 8, and 23 genes, respectively. The 37 BvMAPKKK genes were unevenly distributed on 9 chromosomes, while 3 BvMAPKKK genes were detected on unknown chromosomes. Members within the same group shared a similar gene structure and conserved motif. A lot of cis-acting regulatory elements related to plant growth and development and response to stresses were distributed in promoter regions of BvMAPKKKs. Moreover, these BvMAPKKKs displayed differential expression patterns in sugar beet tissues under salinity condition. The expression levels of the BvRaf30 and BvZIK8-1 in roots and BvRaf17 and BvZIK4 in shoots were markedly induced under salt conditions, which may be an indicator of potential roles in the response to salinity. The present work is the first systematic analysis of the BvMAPKKK gene family in sugar beet. These results could provide a solid foundation for further exploring functions of the MAPKKK genes in plant of responses to salt stress.