Fine-mapping of SRT7 for short roots and identification of its candidate in rice

Abstract

Three allelic short root mutants were identified by screening mutants with defective root elongation of the rice japonica cultivar Nipponbare mutant library generated via 60Co γ-ray irradiation mutagenesis. These mutants, designated srt7-1 (short root 7-1), srt7-2 and srt7-3, respectively, had an extremely short seminal root, adventitious roots and lateral roots. Histological observation revealed the cell length of srt7 mutant roots was significantly shorter than that of wild-type roots. Genetic analysis indicated the short root phenotype was controlled by a single recessive nuclear gene. The SRT7 gene was mapped to a 20-kb interval between the markers STS6 and STS7 on chromosome 4 by a map-based cloning method. Sequencing of the six predicted genes in this region found that all of the three allelic mutants contained a 1-bp or 2-bp deletion in the same gene encoding a putative membrane-bound endo-1,4-β-glucanase. The SRT7 gene was expressed ubiquitously, with higher levels of transcript accumulation in roots at different developmental stages. However, no difference was found in the SRT7 transcription level between the mutant and wild type. Collectively, these results indicate the endo-1,4-β-glucanase encoding gene (LOC_Os04g41970) is likely the candidate for SRT7 that functions posttranscriptionally in rice root elongation.