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Reproductive isolation is an obstacle for plant breeding when a distant cross is demanded. It can be divided into two main types based on different growth stages: prezygotic isolation and postzygotic isolation. The hybrid weakness, which is a type of postzygotic isolation, can become a problem in crop breeding. In order to overcome reproductive isolation, it is necessary to elucidate its mechanism. In this study, genetic analysis for low temperature-dependent hybrid weakness was conducted in a rice F2 population derived from Taichung 65 (T65, Japonica) and Lijiangxintuanheigu (LTH, Japonica). The weak and severe weak plants in F2 showed shorter culm length, late heading, reduced panicle number, decreased grain numbers per panicle, and impaired root development in the field. Our result also showed that hybrid weakness was affected by temperature. It was observed that 24°C enhanced hybrid weakness, whereas 34°C showed recovery from hybrid weakness. In terms of the morphology of embryos, no difference was observed. Therefore, hybrid weakness affects postembryonic development and is independent of embryogenesis. The genotypes of 126 F2 plants were determined through genotyping-by-sequencing and a linkage map consisting of 862 single nucleotide polymorphism markers was obtained. Two major quantitative trait loci (QTLs) were detected on chromosomes 1 [ hybrid weakness j 1 (hwj1)] and 11 [ hybrid weakness j 2 (hwj2)]. Further genotyping indicated that the hybrid weakness was due to an incompatible interaction between the T65 allele of hwj1 and the LTH allele of hwj2. A large F2 populations consisting of 5,722 plants were used for fine mapping of hwj1 and hwj2. The two loci, hwj1 and hwj2 , were mapped in regions of 65-kb on chromosome 1 and 145-kb on chromosome 11, respectively. For hwj1 , the 65-kb region contained 11 predicted genes, while in the hwj2 region, 22 predicted genes were identified, two of which are disease resistance-related genes. The identified genes along these regions serve as preliminary information on the molecular networks associated with hybrid weakness in rice. [ABSTRACT FROM AUTHOR]

Abstract: Chloris virgata Swartz (C. virgata) is a gramineous wild plant that can survive in saline-alkali areas in northeast China. To examine the tolerance mechanisms of C. virgata, we constructed a cDNA library from whole plants of C. virgata that had been treated with 100 mM NaHCO3 for 24 h and sequenced 3168 randomly selected clones. Most (2590) of the expressed sequence tags (ESTs) showed significant similarity to sequences in the NCBI database. Of the 2590 genes, 1893 were unique. Gene Ontology (GO) Slim annotations were obtained for 1081 ESTs by BLAST2GO and it was found that 75 genes of them were annotated with GO terms “response to stress”, “response to abiotic stimulus”, and “response to biotic stimulus”, indicating these genes were likely to function in tolerance mechanism of C. virgata. In a separate experiment, 24 genes that are known from previous studies to be associated with abiotic stress tolerance were further examined by real-time RT-PCR to see how their expressions were affected by NaHCO3 stress. NaHCO3 treatment up-regulated the expressions of pathogenesis-related gene (DC998527), Win1 precursor gene (DC998617), catalase gene (DC999385), ribosome inactivating protein 1 (DC999555), Na+/H+ antiporter gene (DC998043), and two-component regulator gene (DC998236). [Copyright &y& Elsevier]

The development of a plastic root system is essential for stable crop production under variable environments. Rice plants have two types of lateral roots (LRs): S-type (short and thin) and L-type (long, thick, and capable of further branching). LR types are determined at the primordium stage, with a larger primordium size in L-types than S-types. Despite the importance of LR types for rice adaptability to variable water conditions, molecular mechanisms underlying the primordium size control of LRs are unknown. Here, we show that two WUSCHEL-related homeobox ( WOX ) genes have opposing roles in controlling LR primordium (LRP) size in rice. Root tip excision on seminal roots induced L-type LR formation with wider primordia formed from an early developmental stage. QHB/OsWOX5 was isolated as a causative gene of a mutant that is defective in S-type LR formation but produces more L-type LRs than wild-type (WT) plants following root tip excision. A transcriptome analysis revealed that OsWOX10 is highly up-regulated in L-type LRPs. OsWOX10 overexpression in LRPs increased the LR diameter in an expression-dependent manner. Conversely, the mutation in OsWOX10 decreased the L-type LR diameter under mild drought conditions. The qhb mutants had higher OsWOX10 expression than WT after root tip excision. A yeast one-hybrid assay revealed that the transcriptional repressive activity of QHB was lost in qhb mutants. An electrophoresis mobility shift assay revealed that OsWOX10 is a potential target of QHB. These data suggest that QHB represses LR diameter increase, repressing OsWOX10 Our findings could help improve root system plasticity under variable environments., Competing Interests: The authors declare no competing interest., (Copyright © 2021 the Author(s). Published by PNAS.)