Genome-Wide Identification of the CAT Genes and Molecular Characterization of Their Transcriptional Responses to Various Nutrient Stresses in Allotetraploid Rapeseed

<i>Brassica napus</i> is an important oil crop in China and has a great demand for nitrogen nutrients. Cationic amino acid transporters (CAT) play a key role in amino acid absorption and transport in plants. However, the <i>CATs</i> family has not been reported in <i>B. napus</i> so far. In this study, genome-wide analysis identified 22 <i>CAT</i> members in the <i>B. napus</i> genome. Based on phylogenetic and synteny analysis, <i>BnaCATs</i> were classified into four groups (Group I-Group IV). The members in the same subgroups showed similar physiochemical characteristics and intron/exon and motif patterns. By evaluating <i>cis</i>-elements in the promoter regions, we identified some <i>cis</i>-elements related to hormones, stress and plant development. Darwin's evolutionary analysis indicated that <i>BnaCATs</i> might have experienced strong purifying selection pressure. The <i>BnaCAT</i> family may have undergone gene expansion; the chromosomal location of <i>BnaCATs</i> indicated that whole-genome replication or segmental replication may play a major driving role. Differential expression patterns of <i>BnaCATs</i> under nitrate limitation, phosphate shortage, potassium shortage, cadmium toxicity, ammonium excess and salt stress conditions indicated that they were responsive to different nutrient stresses. In summary, these findings provide a comprehensive survey of the <i>BnaCAT</i> family and lay a foundation for the further functional analysis of family members.