Arabidopsis thaliana HYPONASTIC LEAVES1 (HYL1) is a microRNA (miRNA) biogenesis protein that contains two N-terminal double-stranded RNA binding domains (dsRBDs), a putative nuclear localization site (NLS), and a putative protein-protein interaction domain. The interaction of HYL1 with DICER-LIKE1 is important for the efficient and precise processing of miRNA primary transcripts in plant miRNA biogenesis. To define the roles of the various domains of HYL1 in miRNA processing and the miRNA-directed phenotype, we transferred a series of HYL1 deletion constructs into hyl1 null mutants. The N-terminal region containing dsRBD1 and dsRBD2 completely rescued the mutant phenotype of hyl1, triggering the accumulation of miR166 and miR160 and resulting in reduced mRNA levels of the targeted genes. In vivo biochemical analysis of the HYL1-containing complexes from the transgenic plants revealed that the N-terminal dsRBDs of HYL1 were sufficient for processing miRNA precursors and the generation of mature miRNA. Transient and stable expression analysis demonstrated that the putative NLS domain was indeed the nuclear localization signal, whereas the N-terminal region containing the dsRBDs was not restricted to the nucleus. We suggest that the N-terminal dsRBDs fulfill the function of the whole HYL1 and thus play an essential role in miRNA processing and miRNA-directed silencing of targeted genes.

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Triticum turgidum L var. durum is known to be particularly susceptible to infection by Fusarium graminearum, the causal agent for Fusarium head blight (FHB), which results in severe yield losses and grain contaminated with mycotoxins. This research was aimed at identifying FHB resistance in tetraploid wheat and mapping the location of FHB resistance genes. A tetraploid cross of durum wheat ('Strongfield') x Triticum carthlicum ('Blackbird') was used to generate a doubled-haploid (DH) population. This population was evaluated for type II resistance to F. graminearum in replicated greenhouse trials, in which heads were innoculated and the percent of infected spikelets was determined 21 days later. The population was also genotyped with microsatellite markers to construct a map of 424 loci, covering 2 052 cM. The FHB reaction and genotypic data were used to identify FHB resistance quantitative trait loci (QTLs). It was determined that 2 intervals on chromosomes 2BL and 6BS controlled FHB resistance in this tetraploid cross. The FHB resistance allele on chromosome 2BL (r2=0.26, logarithm of odds (LOD)=8.5) was derived from 'Strongfield', and the FHB resistance allele on chromosome 6BS (r2=0.23, LOD=6.6) was derived from 'Blackbird'. Two other loci, on chromosomes 5AS and 2AL, were shown to regulate FHB infection and to have an epistatic effect on the FHB resistance QTL on chromosome 6BS. Further, the FHB resistance QTL peak on chromosome 6BS was clearly coincident with the known FHB resistance gene Fhb2, derived from Sumai 3. The results show that FHB resistance can be expressed in durum wheat, and that T. carthlicum and Triticum aestivum likely share a common FHB resistance gene on chromosome 6BS.