Transcriptomes That Confer to Plant Defense against Powdery Mildew Disease in Lagerstroemia indica

Abstract

Transcriptome analysis was conducted in two popular Lagerstroemia cultivars: "Natchez" (NAT), a white flower and powdery mildew resistant interspecific hybrid and "Carolina Beauty" (CAB), a red flower and powdery mildew susceptible L. indica cultivar. RNA-seq reads were generated from Erysiphe australiana infected leaves and de novo assembled. A total of 37,035 unigenes from 224,443 assembled contigs in both genotypes were identified. Approximately 85% of these unigenes have known function. Of them, 475 KEGG genes were found significantly different between the two genotypes. Five of the top ten differentially expressed genes (DEGs) involved in the biosynthesis of secondary metabolites (plant defense) and four in flavonoid biosynthesis pathway (antioxidant activities or flower coloration). Furthermore, 5 of the 12 assembled unigenes in benzoxazinoid biosynthesis and 7 of 11 in flavonoid biosynthesis showed higher transcript abundance in NAT. The relative abundance of transcripts for 16 candidate DEGs (9 from CAB and 7 from NAT) detected by qRT-PCR showed general agreement with the abundances of the assembled transcripts in NAT. This study provided the first transcriptome analyses in L. indica. The differential transcript abundance between two genotypes indicates that it is possible to identify candidate genes that are associated with the plant defenses or flower coloration.

Figure 1

Length distribution of unigenes in the assembled transcriptomes of two Lagerstroemia indica cultivars: powdery mildew susceptible (Carolina Beauty, CAB) and powdery mildew resistant (Natchez, NAT).

Figure 2

Distribution of active genes in two Lagerstroemia indica cultivars: powdery mildew susceptible (“Carolina Beauty,” CAB) and powdery mildew resistant (“Natchez,” NAT) transcriptomes. (a) KEGG database based gene annotation. (b) Top 20 active KEGG pathways based on the number of unigenes.

Figure 3

Differentially expressed genes (DEGs) identified by different statistical methods (a) and global review of differentially expressed genes in powdery mildew resistant (red dot) and susceptible (black dot) genotypes in Lagerstroemia indica species (b).

Figure 4

Pathway enrichment based on the profile of combined unique gene expression.

Figure 5

Genes encoding enzyme commission (ECs) in flavonoid biosynthesis pathway were upregulated (red) in the transcriptome of resistant crape myrtle genotype (“Natchez,” NAT) compared to susceptible crape myrtle genotype (“Carolina Beauty,” CAB) transcriptome.

Figure 6

(a) Phylogenetic distance of genes encoding methyltransferases to produce DIMBOA-glucoside. (b) Comparison of transcripts abundance (reads per million, RPM) assembled unigenes encoding methyltransferases.

Figure 7

(a) Phylogenetic distance of unigenes encoding flavonoid 3′-monooxygenase to produce flavonoids. (b) Comparison of transcripts abundance (reads per million, RPM) assembled unigenes encoding flavonoid 3′-monooxygenase.