DRB4-dependent TAS3 trans-acting siRNAs control leaf morphology through AGO7

Area of Science:

• Plant molecular biology
• RNA interference pathways
• Arabidopsis genetics

Background:

• Trans-acting siRNAs (ta-siRNAs) are endogenous small RNAs regulating gene expression by targeting complementary mRNAs for cleavage.
• The biogenesis of ta-siRNAs involves microRNA (miRNA) cleavage of TAS gene transcripts, followed by protection, dsRNA synthesis, and Dicer-like 4 (DCL4) processing.

Purpose of the Study:

• To investigate the roles of specific ta-siRNAs, particularly TAS3, in Arabidopsis development.
• To elucidate the genetic pathways and protein interactions involved in ta-siRNA production and function.

Main Methods:

• Analysis of hypomorphic and null mutants in Arabidopsis, including rdr6, sgs3, tas3, ago7/zip, and drb4.
• Quantification of ta-siRNA levels (TAS1, TAS2, TAS3) and target mRNA accumulation (ARF3/ETTIN, ARF4).
• Assessment of leaf morphology and developmental phenotypes in various mutant backgrounds.

Main Results:

• Null rdr6 and sgs3 mutants lack TAS1, TAS2, and TAS3 ta-siRNAs and show defects in posttranscriptional gene silencing and virus resistance.
• TAS3 ta-siRNAs, but not TAS1 or TAS2, are essential for proper leaf development, as evidenced by leaf morphology defects in tas3 mutants.
• The dsRNA binding protein DRB4 is required for ta-siRNA production, likely through interaction with DCL4, and TAS3 ta-siRNAs function via AGO7/ZIPPY.

Conclusions:

• TAS3 ta-siRNAs play a critical role in Arabidopsis leaf development.
• The biogenesis of ta-siRNAs involves a complex interplay of proteins including RDR6, SGS3, DCL4, and DRB4.
• AGO7/ZIPPY mediates the developmental effects of TAS3 ta-siRNAs.