ASR5 is involved in the regulation of miRNA expression in rice.

KEY MESSAGE: The work describes an ASR knockdown transcriptomic analysis by deep sequencing of rice root seedlings and the transactivation of ASR cis-acting elements in the upstream region of a MIR gene. MicroRNAs are key regulators of gene expression that guide post-transcriptional control of plant development and responses to environmental stresses. ASR (ABA, Stress and Ripening) proteins are plant-specific transcription factors with key roles in different biological processes. In rice, ASR proteins have been suggested to participate in the regulation of stress response genes. This work describes the transcriptomic analysis by deep sequencing two libraries, comparing miRNA abundance from the roots of transgenic ASR5 knockdown rice seedlings with that of the roots of wild-type non-transformed rice seedlings. Members of 59 miRNA families were detected, and 276 mature miRNAs were identified. Our analysis detected 112 miRNAs that were differentially expressed between the two libraries. A predicted inverse correlation between miR167abc and its target gene (LOC_Os07g29820) was confirmed using RT-qPCR. Protoplast transactivation assays showed that ASR5 is able to recognize binding sites upstream of the MIR167a gene and drive its expression in vivo. Together, our data establish a comparative study of miRNAome profiles and is the first study to suggest the involvement of ASR proteins in miRNA gene regulation.

New insights into aluminum tolerance in rice: the ASR5 protein binds the STAR1 promoter and other aluminum-responsive genes.

Aluminum (Al) toxicity in plants is one of the primary constraints in crop production. Al³âº, the most toxic form of Al, is released into soil under acidic conditions and causes extensive damage to plants, especially in the roots. In rice, Al tolerance requires the ASR5 gene, but the molecular function of ASR5 has remained unknown. Here, we perform genome-wide analyses to identify ASR5-dependent Al-responsive genes in rice. Based on ASR5_RNAi silencing in plants, a global transcriptome analysis identified a total of 961 genes that were responsive to Al treatment in wild-type rice roots. Of these genes, 909 did not respond to Al in the ASR5_RNAi plants, indicating a central role for ASR5 in Al-responsive gene expression. Under normal conditions, without Al treatment, the ASR5_RNAi plants expressed 1.756 genes differentially compared to the wild-type plants, and 446 of these genes responded to Al treatment in the wild-type plants. Chromatin immunoprecipitation followed by deep sequencing identified 104 putative target genes that were directly regulated by ASR5 binding to their promoters, including the STAR1 gene, which encodes an ABC transporter required for Al tolerance. Motif analysis of the binding peak sequences revealed the binding motif for ASR5, which was confirmed via in vitro DNA-binding assays using the STAR1 promoter. These results demonstrate that ASR5 acts as a key transcription factor that is essential for Al-responsive gene expression and Al tolerance in rice.

Identification of the soybean HyPRP family and specific gene response to Asian soybean rust disease.

Soybean [Glycine max (L.) Merril], one of the most important crop species in the world, is very susceptible to abiotic and biotic stress. Soybean plants have developed a variety of molecular mechanisms that help them survive stressful conditions. Hybrid proline-rich proteins (HyPRPs) constitute a family of cell-wall proteins with a variable N-terminal domain and conserved C-terminal domain that is phylogenetically related to non-specific lipid transfer proteins. Members of the HyPRP family are involved in basic cellular processes and their expression and activity are modulated by environmental factors. In this study, microarray analysis and real time RT-qPCR were used to identify putative HyPRP genes in the soybean genome and to assess their expression in different plant tissues. Some of the genes were also analyzed by time-course real time RT-qPCR in response to infection by Phakopsora pachyrhizi, the causal agent of Asian soybean rust disease. Our findings indicate that the time of induction of a defense pathway is crucial in triggering the soybean resistance response to P. pachyrhizi. This is the first study to identify the soybean HyPRP group B family and to analyze disease-responsive GmHyPRP during infection by P. pachyrhizi.