A rice β-1,3-glucanase gene Osg1 is required for callose degradation in pollen development

Abstract

Plant β-1,3-glucanases are involved in plant defense and development. In rice (Oryza sativa), 14 genes encoding putative β-1,3-glucanases have been isolated and sequenced. However, only limited information is available on the function of these β-1,3-glucanase genes. In this study, we report a detailed functional characterization of one of these genes, Osg1. Osg1 encodes a glucanase carrying no C-terminal extension. Osg1 was found to be expressed throughout the plant and highly expressed in florets, leaf sheaths, and leaf blades. Investigations using real-time PCR, immunocytochemical analysis, and a GUS-reporter gene driven by the Osg1 promoter indicated that Osg1 was mainly expressed at the late meiosis, early microspore, and middle microspore stages in the florets. To elucidate the role of Osg1, we suppressed expression of the Osg1 gene by RNA interference in transgenic rice. The silencing of Osg1 resulted in male sterility. The pollen mother cells appeared to be normal in Osg1-RI plants, but callose degradation was disrupted around the microspores in the anther locules of the Osg1-RI plants at the early microspore stage. Consequently, the release of the young microspores into the anther locules was delayed, and the microspores began to degenerate later. These results provide evidence that Osg1 is essential for timely callose degradation in the process of tetrad dissolution.

The Rice Basic Helix-Loop-Helix Transcription Factor TDR INTERACTING PROTEIN2 Is a Central Switch in Early Anther Development

“…In agreement with the tip2 defect in callose degradation, we detected reduced expression of three glucanase-encoding genes putatively related to callose degradation, including G1 (Wan et al, 2011), and two homologs of Arabidopsis A6 (Hird et al, 1993) in rice, Os09g32550 and Os08g41410 (Supplemental Figure 13). In addition, other genes involved in tapetum late function, including those related to lipid metabolism and transport, such as CYP703A3 (Aya et al, 2009), CYP704B2 , C6 , and DEFECTIVE POLLEN WALL (DPW) (Shi et al, 2011), also exhibited significantly decreased transcription in tip2 (Supplemental Figure 13).…”

Expression Vector Construction and Genetic Transformation of <i>Rosa rugosa β</i>-l,3-Glucanase Gene (<i>RrGlu</i>)

“…Moreover, β-l,3-glucanase is unevenly distributed in a plant. It is barely detectable in young leaves [23] [24]. Our preliminary studies support this concept.…”

Genetic and Biochemical Mechanisms of Pollen Wall Development

“…The portions (GSL1 and GSL12) [14], and rice GSL5 [15] are required for callose wall formation during microspore formation; mutants of these genes display defective callose synthesis and exine patterning [13]. Knockout or knockdown of the A6 gene (which encodes a b-1,3-glucanase) in Arabidopsis, Brassicas, and rice frequently causes defective callose degradation [16,17].…”