The cellulose synthase, AgCESA5, induces cellulose biosynthesis during cell walls formation in celery

Celery (Apium graveolens L.), an important green leafy vegetable in the Apiaceae family, is rich in various nutrients including dietary fiber. Cellulose is a major component of the celery cell walls and serves as the primary substrate for saccharification. Here, we characterized a cellulose synthase, AgCESA5, that positively regulates cellulose accumulation in celery. The AgCESA5 protein was localized in the plasma membrane. Homologous overexpression of AgCESA5 in 'Jinnan Shiqin' celery revealed increased cellulose content in the petioles of transgenic plants and a looser structural texture of parenchyma cell walls. Furthermore, we identified two R2R3-MYB transcription factors, designated AgMYB59 and AgMYB6, that physically bind to the AgCESA5 promoter, as validated by yeast one-hybrid and dual-luciferase reporter assays. Both AgMYB6 and AgMYB59 exhibited transcriptional activation activity and were localized to the nucleus. In the petioles of five celery cultivars, the relative expression levels of AgMYB59 and AgMYB6 showed expression patterns highly consistent with that of AgCESA5 at both 70 and 100 days after germination. Collectively, these results indicate that AgCESA5 is involved in celery cellulose synthesis. AgMYB59 and AgMYB6 may play important roles in cellulose biosynthesis as regulators of AgCESA5.