Differentiated cuticular wax content and expression patterns of cuticular wax biosynthetic genes in bloomed and bloomless broccoli (Brassica oleracea var. italica)

The aerial surfaces of plants are covered with a wax layer that serves the essential functions of limiting non-stomatal water loss and acting as protective barrier against environmental stresses. We selected two broccoli lines, bloomed (MC91) and bloomless (MC117), and analyzed their phenotypes related to cuticular wax accumulation. The total wax amount was 1.93-fold higher in MC91 leaves compared to MC117 leaves. All of the studied cuticular wax compounds were 1.07-3.79-fold higher in MC91 plants compared to MC117 plants except for the C31 alkane. The wax compositions did not essentially different between the two broccoli lines, but some compounds were found at significantly higher levels in MC91 plants compared to MC117 plants, mainly reflecting differences in C29 alkanes, C29 secondary alcohols and C29 ketones. To investigate gene regulation by bloom phenotype, we analyzed the mRNA expression patterns of various cuticular wax biosynthetic genes. Our results revealed that LACS1, KCS1, KCR1, ECR, CER3 and MAH1 were expressed more in MC91 plants compared to MC117 plants at both 3 and 10 weeks. The expression levels of the studied cuticular wax biosynthetic genes were significantly induced by drought stress, which is known to induce cuticular wax deposition. Together, these results show that the cuticular wax accumulation of broccoli is regulated by cuticular wax biosynthetic gene expression and can be affected by environmental signals.