CsBZR1-CsCEL1 module regulates the susceptibility of cucumber to Meloidogyne incognita by mediating cellulose metabolism

Plant-parasitic root knot nematode is a pernicious menace to agriculture. Therefore, uncovering the mechanism of nematode infection is a critical task for crop improvement. Here, with cucumber as material, we found that CsCEL1, encoding β-1,4-endoglucanase to facilitate cellulose degradation, was profoundly induced in the root infected by Meloidogyne incognita. Intriguingly, suppressing the expression of CsCEL1 in cucumber conferred resistance to M. incognita infection with reduced activity of β-1,4-endoglucanase but promoted cellulose in the root. Conversely, overexpressing CsCEL1 in Arabidopsis increased the number of nematode-induced galls. These results suggest that CsCEL1 negatively regulates the resistance to M. incognita. Furthermore, we verified the transcriptional activation of CsCEL1 by CsBZR1, a key transcription factor involved in brassinosteroid signaling. Suppressing the expression of CsBZR1 in cucumber significantly reduced the size and number of galls and suppressed giant cell formation, with promoted cellulose content. Conversely, overexpressing CsBZR1 in Arabidopsis decreased resistance to M. incognita. Exogenous application of brassinosteroid to cucumber suppressed both CsCEL1 and CsBZR1 expressions, significantly reduced the gall numbers, thus improved resistance to M. incognita. Collectively, these results suggest that the CsBZR1–CsCEL1 module is implicated in modulating cellulose content, which may influence M. incognita infection. The finding provides novel insight into the molecular regulations of nematode resistance for breeding resistant varieties or nematode management.