Abstract
In angiosperms, anther development comprises of various complex and interrelated biological processes, critically needed for pollen viability. The transitory callose layer serves to separate the meiocytes. It helps in primexine formation, while the timely degradation of tapetal cells is essential for the timely callose wall dissolution and pollen wall formation by providing nutrients for pollen growth. In rice, many genes have been reported and functionally characterized that are involved in callose regulation and pollen wall patterning, including timely programmed cell death (PCD) of the tapetum, but the mechanism of pollen development largely remains ambiguous. We identified and functionally characterized a rice mutant dcet1, having a complete male-sterile phenotype caused by defects in anther callose wall, exine patterning, and tapetal PCD. DCET1 belongs to the RNA recognition motif (RRM)-containing family also called as the ribonucleoprotein (RNP) domain or RNA-binding domain (RBD) protein, having single-nucleotide polymorphism (SNP) substitution from G (threonine-192) to A (isoleucine-192) located at the fifth exon of LOC_Os08g02330, was responsible for the male sterile phenotype in mutant dcet1. Our cytological analysis suggested that DCET1 regulates callose biosynthesis and degradation, pollen exine formation by affecting exine wall patterning, including abnormal nexine, collapsed bacula, and irregular tectum, and timely PCD by delaying the tapetal cell degeneration. As a result, the microspore of dcet1 was swollen and abnormally bursted and even collapsed within the anther locule characterizing complete male sterility. GUS and qRT-PCR analysis indicated that DCET1 is specifically expressed in the anther till the developmental stage 9, consistent with the observed phenotype. The characterization of DCET1 in callose regulation, pollen wall patterning, and tapetal cell PCD strengthens our knowledge for knowing the regulatory pathways involved in rice male reproductive development and has future prospects in hybrid rice breeding.
Highlights
Rice (Oryza sativa L.) is a staple food crop worldwide, feeding around three billion people, nearly half of the global population (Cheng et al, 2007)
Our results provide the first evidence of the RNA recognition motif (RRM)/RNA-binding domain (RBD) family protein DCET1 in rice male sterility through defective callose, exine wall, and tapetal cell programmed cell death (PCD), which justifies its role in hybrid rice breeding
To explore the reproductive system defects of the dcet1 mutant, we investigated the cytological mechanism of WT and dcet1
Summary
Rice (Oryza sativa L.) is a staple food crop worldwide, feeding around three billion people, nearly half of the global population (Cheng et al, 2007). The global population is intensively increasing, and water resources and agricultural land for rice production are shrinking because of urban expansion and climatic changes. Hybrid rice production is one of the key technologies, among the genetic options, to overcome the growing population’s food shortage. Rice is a self-pollinated crop; the male sterility technique is used to develop commercial hybrid parental lines (Chang et al, 2016). Male sterility produces infertile pollens, so that rice spikelets are incapable of setting seeds through self-pollination (Chang et al, 2016). Pollen is the key source for improved rice grain production; understanding the mechanism of pollen development is extremely important for rice breeding (Zhang et al, 2011)
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