Citrus WRKY28 acts as a transcription repressor to modulate cuticular long-chain alkanes accumulation in response to water loss stress

The cuticular wax, composed of very long-chain fatty acids, plays an important role in postharvest preservation. WRKY transcription factors take part in the regulation of stress responses, while the specific roles related to wax metabolism are still not well understood. Herein, a citrus WRKY member, CsWRKY28, was found to regulate alkanes biosynthesis. CsWRKY28 was highly expressed in fruit peel and up-regulated during postharvest storage. Heterologous overexpression of CsWRKY28 in Arabidopsis enhanced drought tolerance, increasing survival rates by more than 40 %, and promoted the biosynthesis of very-long-chain alkanes, elevating total leaf wax load with the most substantial increases observed in C29 and C31 alkanes (approximately 15 %). Similarly, CsWRKY28-overexpressing fruit retained significantly higher alkane levels, with C31 and C33 alkanes increasing by about 10 % and 40 %, respectively, compared to controls. Meanwhile, CsWRKY28 was demonstrated to repress the expression of CsKCS12 , a negative regulator of wax biosynthesis, thereby facilitating alkane accumulation and promoting wax layer maintenance. Our findings provide new information on the regulatory mechanism of wax metabolism in citrus fruit and provide a theoretical basis for the development of citrus variety-specific coating agents. • Postharvest water loss induced the expression of CsWRKY28 in fruit peel . • CsWRKY28 located to the nucleus and functioned as a transcriptional repressor. • Overexpression of CsWRKY28 elevated the accumulation of C29/C31 alkanes. • Citrus WRKY28 directly repressed the wax negative regulator CsKCS12 .