Functional Characterization of CsBAS1, CsSND1, and CsIRX6 in Cucumber Defense Against Meloidogyne incognita

Vascular tissue development plays a pivotal role in plant growth and defense against biotic stress. Root-knot nematodes, particularly <i>Meloidogyne incognita</i> (<i>M. incognita</i>), are globally distributed phytopathogens that cause severe economic losses in a variety of vascular plants. In this study, three vascular bundle development-related genes, including <i>CsBAS1</i>, <i>CsSND1</i>, and <i>CsIRX6</i>, were identified in cucumber. Tissue-specific expression analysis revealed that <i>CsSND1</i> and <i>CsIRX6</i> were highly expressed in roots. Infection with <i>M. incognita</i> showed dynamic expression changes for <i>CsBAS1</i>, <i>CsSND1</i>, and <i>CsIRX6</i>. Specially, <i>CsIRX6</i> and <i>CsSND1</i> were upregulated at 14 days post-inoculation (dpi), while <i>CsBAS1</i> was downregulated at both 7 dpi and 14 dpi. Tissue localization studies using promoter-GUS constructs demonstrated <i>pCsBAS1</i>-<i>GUS</i> and <i>pCsSND1</i>-<i>GUS</i> activity in galls and specific vascular tissues, while <i>CsIRX6</i> mRNA was detected in giant cells (GCs) at 14 dpi using <i>in situ</i> methods. Virus-induced gene silencing (VIGS) of <i>CsBAS1</i>, <i>CsSND1</i>, and <i>CsIRX6</i> revealed their distinct roles in nematode-induced gall formation. Silencing <i>CsBAS1</i> and <i>CsSND1</i> resulted in increased root growth and gall size, whereas silencing <i>CsIRX6</i> led to reduced gall size. These findings highlight the functional significance of <i>CsBAS1</i>, <i>CsSND1</i>, and <i>CsIRX6</i> in cucumber defense against <i>M. incognita</i>, offering insights into the interplay between vascular development and plant defense mechanisms.