Abstract
ROOT UV-B SENSITIVE4 (RUS4) encodes a protein with no known function that contains a conserved Domain of Unknown Function 647 (DUF647). The DUF647-containing proteins RUS1 and RUS2 have previously been associated with root UV-B-sensing pathway that plays a major role in Arabidopsis early seedling morphogenesis and development. Here, we show that RUS4 knockdown Arabidopsis plants, referred to as amiR-RUS4, were severely reduced in male fertility with indehiscent anthers. Light microscopy of anther sections revealed a significantly reduced secondary wall thickening in the endothecium of amiR-RUS4 anthers. We further show that the transcript abundance of the NAC domain genes NAC SECONDARY WALL THICKENING PROMOTING FACTOR1 (NST1) and NST2, which have been shown to regulate the secondary cell wall thickenings in the anther endothecium, were dramatically reduced in the amiR-RUS4 floral buds. Expression of the secondary cell wall-associated MYB transcription factor genes MYB103 and MYB85 were also strongly reduced in floral buds of the amiR-RUS4 plants. Overexpression of RUS4 led to increased secondary thickening in the endothecium. However, the rus4-2 mutant exhibited no obvious phenotype. Promoter-GUS analysis revealed that the RUS4 promoter was highly active in the anthers, supporting its role in anther development. Taken together, these results suggest that RUS4, probably functions redundantly with other genes, may play an important role in the secondary thickening formation in the anther endothecium by indirectly affecting the expression of secondary cell wall biosynthetic genes.
Highlights
Anther dehiscence and pollen maturation are essential processes occurring late in plant anther development; pollen formation typically involves gene expression from more than half of the genome
Using an artificial microRNA approach, we generated constitutive knockdown lines targeting the gene ROOT UV-B SENSITIVE4 (RUS4), which belongs to the Domain of Unknown Function 647 (DUF647) family that is conserved in eukaryotic organisms, but has no known biological function
We present the first evidence for the important role of RUS4 gene in Arabidopsis anther dehiscence by affecting secondary wall thickening in the endothecium
Summary
Anther dehiscence and pollen maturation are essential processes occurring late in plant anther development; pollen formation typically involves gene expression from more than half of the genome. Pollen development occurs within the anther, which contains four cell layers, the epidermis, endothecium, middle layer and tapetum (Scott et al 2004, Zhang and Yang 2014). Endothecium development is coordinated with pollen maturation and the degeneration of the anther tapetum and middle cell layer. The anther endothecium and the localized secondary thickening within this cell layer play a critical role in anther dehiscence and pollen release, as it is responsible for providing the mechanical force for anther opening (Keijzer 1987, Bonner 1989, Wilson et al 2011, Nelson et al, 2012). The main events of the dehiscence program include: the formation of fibrous bands on the endothecial cell walls, degeneration of the septum cells leading to a bilocular anther, and breakage of the stomium and release of pollen grains (Goldberg et al 1993)
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