MicroRNA-Mediated Regulation of Stomatal Development inArabidopsis

Abstract

The proper number and distribution of stomata are essential for the efficient exchange of gases between the atmosphere and the aerial parts of plants. We show that the density and development of stomatal complexes on the epidermis of Arabidopsis thaliana leaves depend, in part, on the microRNA-mediated regulation of Agamous-like16 ( AGL16 ), which is a member of the MADS box protein family. AGL16 mRNA is targeted for sequence-specific degradation by miR824, a recently evolved microRNA conserved in the Brassicaceae and encoded at a single genetic locus. Primary stomatal complexes can give rise to higher-order complexes derived from satellite meristemoids. Expression of a miR824-resistant AGL16 mRNA, but not the wild-type AGL16 mRNA, in transgenic plants increased the incidence of stomata in higher-order complexes. By contrast, reduced expression of AGL16 mRNA in the agl16-1 deficiency mutant and in transgenic lines overexpressing miR824 decreased the incidence of stomata in higher-order complexes. These findings and the nonoverlapping patterns of AGL16 mRNA and miR824 localization led us to propose that the miR824/AGL16 pathway functions in the satellite meristemoid lineage of stomatal development.

Structurally different alleles of the ath- MIR824 microRNA precursor are maintained at high frequency in Arabidopsis thaliana

“…Although both are young with respect to the other loci examined in this and the other study (28), these two miRNA genes may have different ages. miR824 was shown to target AGL16 in Brassica rapa and Brassica napus and probably arose some 24 millions years ago (18,30). miR856 is also not found in Populus or rice, but it is not known whether it is conserved in the Brassicacae or younger.…”

“…Therefore, the two allelic types are equally likely to be functional, despite elevated levels of divergence. Indeed, mature miR824 was detected in both Col-0 and Ler-0 ecotypes, which harbor the long and short allele, respectively (18). In the short allele, a secondary stem-loop structure appears, Ϸ100 bp long, that is well defined (high probability of pairing) and part of the MFE structure (Fig.…”

“…miRNA856 is so far known only in A. thaliana and Arabidopsis lyrata, and miR824 was found only in the Brassicacae (18). The length of pre-miRNA ranged from 95 to 734 bp.…”

“…First, miR824 controls stomata density, and demands on this trait may vary across the climatic range of the species (18). Second, the alleles in the long-allele clade display a secondary structure that is best-defined and most stable at 3°C (see Table 3).…”

Control of stomatal aperture

“…Interestingly, recent evidence suggests that density and development of stomata on the Arabidopsis thaliana leaves depend, in part, on the microRNAmediated regulation of Agamous-like16 (AGL16) gene. 51 AGL16 is a member of the MADS box protein family, which mRNA is targeted for sequence-specific degradation by the microRNA miR824. Additionally several potential quantitative trait loci have been also identified in poplar 52,53 and thus it seems reasonable to assume that leaf traits may be robust enough to be developed as markers for accelerated breeding programs, offering another research approach to increase crop yield.…”