Altered Developmental and Metabolic Gene Expression in Basil Interspecific Hybrids.

To understand the altered developmental changes and associated gene expression in inter-genomic combinations, a study was planned in two diverse yet closely related species of Ocimum, targeting their hybrid F1 and amphidiploids. The existing developmental variations between F1 and amphidiploids was analyzed through phenotypical and anatomical assessments. The absence of 8330 transcripts of F1 in amphidiploids and the exclusive presence of two transcripts related to WNK lysine-deficient protein kinase and geranylgeranyl transferase type-2 subunit beta 1-like proteins in amphidiploids provided a set of genes to compare the suppressed and activated functions between F1 and amphidiploids. The estimation of eugenol and methyleugenol, flavonoid, lignin and chlorophyll content was correlated with the average FPKM and differential gene expression values and further validated through qRT-PCR. Differentially expressed genes of stomatal patterning and development explained the higher density of stomata in F1 and the larger size of stomata in amphidiploids. Gene expression study of several transcription factors putatively involved in the growth and developmental processes of plants clearly amalgamates the transcriptome data linking the phenotypic differences in F1 and amphidiploids. This investigation describes the influence of interspecific hybridization on genes and transcription factors leading to developmental changes and alleviation of intergenomic instability in amphidiploids.

RNAi down-regulation of cinnamate-4-hydroxylase increases artemisinin biosynthesis in Artemisia annua.

Cinnamate-4-hydroxylase (C4H) converts trans-cinnamic acid (CA) to p-coumaric acid (COA) in the phenylpropanoid/lignin biosynthesis pathway. Earlier we reported increased expression of AaCYP71AV1 (an important gene of artemisinin biosynthesis pathway) caused by CA treatment in Artemisia annua. Hence, AaC4H gene was identified, cloned, characterized and silenced in A. annua with the assumption that the elevated internal CA due to knock down may increase the artemisinin yield. Accumulation of trans-cinnamic acid in the plant due to AaC4H knockdown was accompanied with the reduction of p-coumaric acid, total phenolics, anthocyanin, cinnamate-4-hydroxylase (C4H) and phenylalanine ammonia lyase (PAL) activities but increase in salicylic acid (SA) and artemisinin. Interestingly, feeding trans-cinnamic acid to the RNAi line increased the level of artemisinin along with benzoic (BA) and SA with no effect on the downstream metabolites p-coumaric acid, coniferylaldehyde and sinapaldehyde, whereas p-coumaric acid feeding increased the content of downstream coniferylaldehyde and sinapaldehyde with no effect on BA, SA, trans-cinnamic acid or artemisinin. SA is reported earlier to be inducing the artemisinin yield. This report demonstrates the link between the phenylpropanoid/lignin pathway with artemisinin pathway through SA, triggered by accumulation of trans-cinnamic acid because of the blockage at C4H.