Altered expression levels of long noncoding natural antisense transcripts overlapping the UGT73C6 gene affect rosette size in Arabidopsis thaliana.

Natural antisense long noncoding RNAs (lncNATs) are involved in the regulation of gene expression in plants, modulating different relevant developmental processes and responses to various stimuli. We have identified and characterized two lncNATs (NAT1 UGT73C6 and NAT2 UGT73C6 , collectively NATs UGT73C6 ) from Arabidopsis thaliana that are transcribed from a gene fully overlapping UGT73C6, a member of the UGT73C subfamily of genes encoding UDP-glycosyltransferases (UGTs). Expression of both NATs UGT73C6 is developmentally controlled and occurs independently of the transcription of UGT73C6 in cis. Downregulation of NATs UGT73C6 levels through artificial microRNAs results in a reduction of the rosette area, while constitutive overexpression of NAT1 UGT73C6 or NAT2 UGT73C6 leads to the opposite phenotype, an increase in rosette size. This activity of NATs UGT73C6 relies on its RNA sequence, and, although modulation of UGT73C6 in cis cannot be excluded, the observed phenotypes are not a consequence of the regulation of UGT73C6 in trans. The NATs UGT73C6 levels were shown to affect cell proliferation and thus individual leaf size. Consistent with this concept, our data suggest that the NATs UGT73C6 influence the expression levels of key transcription factors involved in regulating leaf growth by modulating cell proliferation. These findings thus reveal an additional regulatory layer on the process of leaf growth.