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Rice mitochondrial aldehyde dehydrogenase OsALDH2b contributes to tapetal degradation, which is essential for male fertility., Timely degradation of anther tapetal cells is a prerequisite for normal pollen development in flowering plants. Although several genes involved in tapetum development have been identified, the molecular basis of tapetum degeneration regulation remains poorly understood. In this study, we identified and characterized the nucleus-encoded, conserved mitochondrial aldehyde dehydrogenase OsALDH2b as a key regulator of tapetum degeneration in rice (Oryza sativa). OsALDH2b was highly expressed in anthers from meiosis to the early microspore stage. Mutation of OsALDH2b resulted in excess malonaldehyde accumulation and earlier programmed cell death in the tapetum, leading to premature tapetum degeneration and abnormal microspore development. These results demonstrate that OsALDH2b negatively regulates tapetal programmed cell death and is required for male reproductive development, providing insights into the regulation of tapetum development in plants.

In many diploid organisms, the majority mutations induced by clustered regularly interspaced short palindromic repeats (CRISPR)-mediated genome editing are non- chimeric, including biallelic, homozygous, and heterozygous mutations. Direct Sanger sequencing of the PCR amplicons containing non-homozygous mutations superimposes sequencing chromatograms, displaying overlapping peaks beginning from the mutation sites. In this chapter we describe the degenerate sequence decoding (DSD) strategy and its automatic web-based tool, DSDecodeM, for decoding the Sanger sequencing chromatograms from different types of targeted mutations. DSDecodeM, as a convenient and versatile tool, can considerably facilitate the genotyping work of CRISPR-induced mutants.

In many diploid organisms, the majority mutations induced by clustered regularly interspaced short palindromic repeats (CRISPR)-mediated genome editing are non- chimeric, including biallelic, homozygous, and heterozygous mutations. Direct Sanger sequencing of the PCR amplicons containing non-homozygous mutations superimposes sequencing chromatograms, displaying overlapping peaks beginning from the mutation sites. In this chapter we describe the degenerate sequence decoding (DSD) strategy and its automatic web-based tool, DSDecodeM, for decoding the Sanger sequencing chromatograms from different types of targeted mutations. DSDecodeM, as a convenient and versatile tool, can considerably facilitate the genotyping work of CRISPR-induced mutants.

CRISPR/Cas9 genome targeting systems have been applied to a variety of species. However, most CRISPR/Cas9 systems reported for plants can only modify one or a few target sites. Here, we report a robust CRISPR/Cas9 vector system, utilizing a plant codon optimized Cas9 gene, for convenient and high-efficiency multiplex genome editing in monocot and dicot plants. We designed PCR-based procedures to rapidly generate multiple sgRNA expression cassettes, which can be assembled into the binary CRISPR/Cas9 vectors in one round of cloning by Golden Gate ligation or Gibson Assembly. With this system, we edited 46 target sites in rice with an average 85.4% rate of mutation, mostly in biallelic and homozygous status. We reasoned that about 16% of the homozygous mutations in rice were generated through the non-homologous end-joining mechanism followed by homologous recombination-based repair. We also obtained uniform biallelic, heterozygous, homozygous, and chimeric mutations in Arabidopsis T1 plants. The targeted mutations in both rice and Arabidopsis were heritable. We provide examples of loss-of-function gene mutations in T0 rice and T1 Arabidopsis plants by simultaneous targeting of multiple (up to eight) members of a gene family, multiple genes in a biosynthetic pathway, or multiple sites in a single gene. This system has provided a versatile toolbox for studying functions of multiple genes and gene families in plants for basic research and genetic improvement.

Recently, genome editing technologies have shown great potential in plants. The newly developed clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 system is a new generation of genome editing tool rapidly replacing the earlier zinc finger nucleases and transcription activator-like effector nucleases systems. Indeed, due to its advantages of simplicity and high efficiency, the CRISPR/Cas9-based genome editing system is becoming a powerful tool in plant science research. Here, we introduce the technical features of the plant CRISPR/Cas9-based genome editing system and its applications in plant functional genomics studies and genetic improvement.

The transcription activator-like effector nucleases (TALENs) and clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 genome editing systems have greatly improved the efficiency for generating targeted mutations in various organisms including plants (Li et al., 2012; Cong et al., 2013; Li et al., 2013; Feng et al., 2014; Ma et al., 2015b; Zhang et al., 2014, 2015). In some plant species, the majority of mutations induced by TALENs and CRISPR/Cas9 systems are in uniform biallelic and heterozygous status in the first transgenic generation, although in some other plant species, chimeric mutations (with three or more allelic edited events within a single individual) may frequently occur (Li et al., 2013; Feng et al., 2014; Zhang et al., 2014, 2015; Ma et al., 2015b).

The recent development of sequence-specific nuclease systems, i.e., TALENs and CRISPR/Cas9, has made genomic targeting easier in many organisms including plants (Li et al., 2012; Cong et al., 2013; Joung and Sander, 2013; Li, et al., 2013; Shan et al., 2013; Liang et al., 2014; Zhang et al., 2014). Mutations induced by CRISPR/Cas9 usually occur around the cleavage sites at three bases upstream of the protospacer-adjacent motif (PAM), producing insertion and deletion of nucleotides. For diploid organisms, such targeted mutations may happen in one or both homologous chromosomes.

The clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9-mediated genome targeting system has been applied to a variety of organisms, including plants. Compared to other genome-targeting technologies such as zinc-finger nucleases (ZFNs) and transcription activator-like effector nucleases (TALENs), the CRISPR/Cas9 system is easier to use and has much higher editing efficiency. In addition, multiple "single guide RNAs" (sgRNAs) with different target sequences can be designed to direct the Cas9 protein to multiple genomic sites for simultaneous multiplex editing. Here, we present a procedure for highly efficient multiplex genome targeting in monocot and dicot plants using a versatile and robust CRISPR/Cas9 vector system, emphasizing the construction of binary constructs with multiple sgRNA expression cassettes in one round of cloning using Golden Gate ligation. We also describe the genotyping of targeted mutations in transgenic plants by direct Sanger sequencing followed by decoding of superimposed sequencing chromatograms containing biallelic or heterozygous mutations using the Web-based tool DSDecode. © 2016 by John Wiley & Sons, Inc.

The clustered regularly interspaced short palindromic repeat (CRISPR)-associated protein9 (Cas9) genome editing system (CRISPR/Cas9) is adapted from the prokaryotic type II adaptive immunity system. The CRISPR/Cas9 tool surpasses other programmable nucleases, such as ZFNs and TALENs, for its simplicity and high efficiency. Various plant-specific CRISPR/Cas9 vector systems have been established for adaption of this technology to many plant species. In this review, we present an overview of current advances on applications of this technology in plants, emphasizing general considerations for establishment of CRISPR/Cas9 vector platforms, strategies for multiplex editing, methods for analyzing the induced mutations, factors affecting editing efficiency and specificity, and features of the induced mutations and applications of the CRISPR/Cas9 system in plants. In addition, we provide a perspective on the challenges of CRISPR/Cas9 technology and its significance for basic plant research and crop genetic improvement.

Plant mutants are important bio-resources for crop breeding and gene functional studies. Conventional methods for generating mutant libraries by mutagenesis of seeds with physical or chemical agents are of low efficiency. Here, we developed a highly-efficient ethyl methanesulfonate (EMS) mutagenesis system based on suspension-cultured cells, with rice (Oryza sativa L.) as an example. We show that treatment of suspension-cultured tiny cell clusters with 0.4% EMS for 18-22 h followed by differentiation and regeneration produced as high as 29.4% independent mutant lines with visible phenotypic variations, including a number of important agronomic traits such as grain size, panicle size, grain or panicle shape, tiller number and angle, heading date, male sterility, and disease sensitivity. No mosaic mutant was observed in the mutant lines tested. In this mutant library, we obtained a mutant with an abnormally elongated uppermost internode. Sequencing and functional analysis revealed that this is a new allelic mutant of eui (elongated uppermost internode) caused by two point mutations in the first exon of the EUI gene, representing a successful example of this mutagenesis system.