In the past few years, the development of sequence-specific DNA nucleases has progressed rapidly and such nucleases have shown their power in generating efficient targeted mutagenesis and other genome editing applications. For zinc finger nucleases (ZFNs) and transcription activator-like effector nucleases (TALENs), an engineered array of sequence-specific DNA binding domains are fused with the DNA nuclease Fok1. These nucleases have been successful in genome modifications by generating double strand breaks (DSBs), which are then repaired through non-homologous end joining (NHEJ) or homologous recombination (HR) in different species, including mouse, tobacco and rice. Recently, another breakthrough technology for genome editing, the CRISPR/Cas system, was developed. CRISPR (clustered regulatory interspaced short palindromic repeats) loci are variable short spacers separated by short repeats, which are transcribed into non-coding RNAs. The non-coding RNAs form a functional complex with CRISPR-associated (Cas) proteins and guide the complex to cleave complementary invading DNA. After the initial development of a programmable CRISPR/Cas system, it has been rapidly applied to achieve efficient genome editing in human cell lines, zebrafish and mouse. However, there is still no successful application in plants reported.Chinese Academy of Science

Summary: Root hair growth requires intensive cell‐wall modification. This study demonstrates that root hair‐specific expansin As, a sub‐clade of the cell wall‐loosening expansin proteins, are required for root hair elongation in rice (Oryza sativaL.). We identified a gene encodingEXPA17(OsEXPA17) from a rice mutant with short root hairs. Promoter::reporter transgenic lines exhibited exclusiveOsEXPA17expression in root hair cells. The OsEXPA17 mutant protein (OsexpA17) contained a point mutation, causing a change in the amino acid sequence (Gly104→Arg). This amino acid alteration is predicted to disrupt a highly conserved disulfide bond in the mutant. Suppression ofOsEXPA17by RNA interference further confirmed requirement for the gene in root hair elongation. Complementation of theOsEXPA17mutant with other root hair EXPAs (OsEXPA30 and Arabidopsis EXPA7) can restore root hair elongation, indicating functional conservation of these root hair EXPAs in monocots and dicots. These results demonstrate that members of the root hair EXPA sub‐clade play a crucial role in root hair cell elongation in Graminaceae.

• For a better understanding of shoot branching in rice (Oryza sativa), a rice activation‐tagging library was screened for mutations in tiller development. Here, an activation‐tagging mutant Ostil1 (Oryza sativa tillering1) was characterized, which showed increased tillers, enlarged tiller angle and semidwarf phenotype. • Flanking sequence was obtained by plasmid rescue. RNA‐interfering and overexpression transgenic rice plants were produced using Agrobacterium‐mediated transformation. • The mutant phenotype was cosegregated with the reallocation of Ds element, and the flanking region of the reallocated Ds element was identified as part of the OsNAC2 gene. Northern analysis showed that expression of OsNAC2 was greatly induced in the mutant plants. Transgenic rice overexpressing the OsNAC2 resulted in recapture of the mutant phenotype, while downregulation of OsNAC2 in the Ostil1 mutant through RNA interfering (RNAi) complemented the mutant phenotype, confirming that the Ostil1 was caused by overexpression of OsNAC2. • Overexpression of OsNAC2 regulates shoot branching in rice. Overexpression of OsNAC2 contributes tiller bud outgrowth, but does not affect tiller bud initiation. This suggests that OsNAC2 has potential utility for improving plant structure for higher light‐use efficiency and higher yield potential in rice.

Plant roots move through the soil by elongation. This is vital to their ability to anchor the plant and acquire water and minerals from the soil. In order to identify new genes involved in root elongation in rice, we screened an ethyl methane sulfonate (EMS)-mutagenized rice library, and isolated a short root mutant, Osglu3-1. The map-based cloning results showed that the mutant was due to a point mutation in OsGLU3, which encodes a putative membrane-bound endo-1,4-β-glucanase. Osglu3-1 displayed less crystalline cellulose content in its root cell wall, shorter root cell length, and a slightly smaller root meristem as visualized by restricted expression of OsCYCB1,1:GUS. Exogenous application of glucose can suppress both the lower root cell wall cellulose content and short root phenotypes of Osglu3-1. Consistently, OsGLU3 is ubiquitously expressed in various tissues with strong expression in root tip, lateral root, and crown root primodia. The fully functional OsGLU3-GFP was detected in plasma membrane, and FM4-64-labeled compartments in the root meristem and elongation zones. We also found that phosphate starvation, an environmental stress, altered cell wall cellulose content to modulate root elongation in a OsGLU3-dependant way.