COLLAPSED ABNORMAL POLLEN1Gene Encoding the Arabinokinase-Like Protein Is Involved in Pollen Development in Rice      

Abstract

We isolated a pollen-defective mutant, collapsed abnormal pollen1 (cap1), from Tos17 insertional mutant lines of rice (Oryza sativa). The cap1 heterozygous plant produced equal numbers of normal and collapsed abnormal grains. The abnormal pollen grains lacked almost all cytoplasmic materials, nuclei, and intine cell walls and did not germinate. Genetic analysis of crosses revealed that the cap1 mutation did not affect female reproduction or vegetative growth. CAP1 encodes a protein consisting of 996 amino acids that showed high similarity to Arabidopsis (Arabidopsis thaliana) L-arabinokinase, which catalyzes the conversion of L-arabinose to L-arabinose 1-phosphate. A wild-type genomic DNA segment containing CAP1 restored mutants to normal pollen grains. During rice pollen development, CAP1 was preferentially expressed in anthers at the bicellular pollen stage, and the effects of the cap1 mutation were mainly detected at this stage. Based on the metabolic pathway of L-arabinose, cap1 pollen phenotype may have been caused by toxic accumulation of L-arabinose or by inhibition of cell wall metabolism due to the lack of UDP-L-arabinose derived from L-arabinose 1-phosphate. The expression pattern of CAP1 was very similar to that of another Arabidopsis homolog that showed 71% amino acid identity with CAP1. Our results suggested that CAP1 and related genes are critical for pollen development in both monocotyledonous and dicotyledonous plants.

Sugar Transporter STP7 Specificity for l-Arabinose and d-Xylose Contrasts with the Typical Hexose Transporters STP8 and STP12

“…The high expression of STP7 in pollen is in line with the assumption that the arabinose salvage pathway plays an important role in developing pollen and contributes to a portion of the pectic arabinan of the pollen cell wall: First, the rice (Oryza sativa) L-arabinokinase CAP1 has been shown to be necessary for the normal development of pollen (Ueda et al, 2013). Additionally, knockdown of USP influences pollen development (Schnurr et al, 2006;Kotake et al, 2007;Geserick and Tenhaken, 2013) as well as the knockdown of UAM3 in rice, where the UAM3 protein is necessary for the conversion of UDP-Ara in the furanose form to UDP-Ara in the pyranose form (Sumiyoshi et al, 2015).…”

Genetic and Biochemical Mechanisms of Pollen Wall Development

“…Recently, GLYCOSYLTRANSFERASE 1 (OsGT1), a Golgi-localized glycosyltransferase [31], and COLLAPSED ABNORMAL POLLEN 1 (CAP1), an ARABI-NOKINASE-like protein [32], were shown to be required for intine development in rice. Mutants of OsGT1 or CAP1 display disrupted intine [31,32].…”

“…Recently, GLYCOSYLTRANSFERASE 1 (OsGT1), a Golgi-localized glycosyltransferase [31], and COLLAPSED ABNORMAL POLLEN 1 (CAP1), an ARABI-NOKINASE-like protein [32], were shown to be required for intine development in rice. Mutants of OsGT1 or CAP1 display disrupted intine [31,32]. Consistent with the hypothesis that pectin is an important component of intine, overexpression of a rhamnogalacturonan lyase or an endo-/-1,5-L-arabinanase, both of which remove the side chains of pectic arabinan, causes the failure of intine formation in transgenic potato plants [33].…”

“…In addition, disturbing the biosynthesis and degradation of callose often results in defective pollen wall development [16,17]. Furthemore, mutation in genes encoding other polysaccharide-associated enzymes also causes abnormal pollen wall development [31,32,36]. Recent transcriptomic analyses also indicated that the expression of polysaccharide metabolism-associated genes in a male-sterile soybean line was significantly downregulated compared to the male-fertile line; these genes encode invertases, hexokinases, and pectin lyases [37].…”

The distinct functions of two classical arabinogalactan proteins BcMF8 and BcMF18 during pollen wall development in Brassica campestris

“…Intine formation is a complicated process involving the activity of numerous genes associated with synthesis of pectin, cellulose, hemicellulose, hydrolytic enzymes and hydrophobic proteins (Ariizumi and Toriyama, 2011). Recently, well-characterized genes in which mutations cause impaired intine and male- sterile phenotype have enriched our understanding of key events in pollen wall development (Fei and Sawhney, 2001;Huang et al, 2009a,b;Moon et al, 2013;Ueda et al, 2013;Jiang et al, 2014a,b;Lou et al, 2014b;Xu et al, 2017). However, the molecular mechanisms underlying intine patterning remain largely elusive.…”