Significance: In cereal crops, the number of florets in a spikelet is an important factor affecting the grain number per panicle and then the grain yield. In wild-type rice, one spikelet produces one fertile floret. This study characterized a gain-of-function mutant lateral florets 1 ( lf1 ) in rice. In lf1 , the spikelet developed lateral florets with proper floral organ identities in the axil of the sterile lemma, showing that the rice spikelet has the potential to restore the “three-florets spikelet” which may have existed in ancestors. Therefore, it provides strong evidence supporting the three-florets spikelet hypothesis and presents a prospect for increasing grain number per panicle by breeding rice with three-floret spikelets.

Background: Tumourous stem mustard (Brassica juncea var. tumida Tsen et Lee) is an economically and nutritionally important vegetable crop of the Cruciferae family that also provides the raw material for Fuling mustard. The genetics breeding, physiology, biochemistry and classification of mustards have been extensively studied, but little information is available on tumourous stem mustard at the molecular level. To gain greater insight into the molecular mechanisms underlying stem swelling in this vegetable and to provide additional information for molecular research and breeding, we sequenced the transcriptome of tumourous stem mustard at various stem developmental stages and compared it with that of a mutant variety lacking swollen stems. Results: Using Illumina short-read technology with a tag-based digital gene expression (DGE) system, we performed de novo transcriptome assembly and gene expression analysis. In our analysis, we assembled genetic information for tumourous stem mustard at various stem developmental stages. In addition, we constructed five DGE libraries, which covered the strains Yong'an and Dayejie at various development stages. Illumina sequencing identified 146,265 unigenes, including 11,245 clusters and 135,020 singletons. The unigenes were subjected to a BLAST search and annotated using the GO and KO databases. We also compared the gene expression profiles of three swollen stem samples with those of two non-swollen stem samples. A total of 1,042 genes with significantly different expression levels occurring simultaneously in the six comparison groups were screened out. Finally, the altered expression levels of a number of randomly selected genes were confirmed by quantitative real-time PCR. Conclusions: Our data provide comprehensive gene expression information at the transcriptional level and the first insight into the understanding of the molecular mechanisms and regulatory pathways of stem swelling and development in this plant, and will help define new mechanisms of stem development in non-model plant organisms.

As the indispensable part of plant, leaf blade mainly functions as the production workshops where organic substance is produced by photosynthesis. Leaf colour mutation is a genetic phenomenon that has a high frequency and is easily identified. The mutations always exhibit negative impact on the development of plants in any of the different stages of growth. Up to now, numerous genes involved in leaf colour mutations have been cloned. In this study, a yellow-green leaf mutant, yellow-green leaf 8 (ygl8), with stable genetic phenotype, has been screened out in the progeny of an excellent indica restorer line Jinhui 10 with seeds treated by EMS. The levels of Chl a, Chl b and total chlorophyll were significantly lower in ygl8 than those in the WT throughout the whole growth period, while no clear change was noted in the Chl a/b ratio. Transmission electron microscopy demonstrated that the lamellae were clearly intumescent and intricately stacked in ygl8. Furthermore, compared with those of the WT, the stomatal conductance, intercellular CO2 concentration, photosynthetic rate and transpiration rate of ylg8 were all significantly lower. Map-based cloning results showed that Loc_Os01g73450, encoding a chloroplast-targeted UMP kinase, corresponded to Ygl8 and played an important role in regulating leaf colour in rice (Oryza sativa). Complementation of ygl8 with the WT DNA sequence of Loc_Os01g73450 led to restoration of the normal phenotype, and transgenic RNA interference plants showed a yellow-green colour. Analysis of the spatial and temporal expression of Ygl8 indicated that it was highly expressed in leaf blades and weakly expressed in other tissues. qRT-PCR also showed that the expression levels of the major Photosystem I core subunits plastome-encoded PsaA, PsaB and PsbC were significantly reduced in ygl8. The expression levels of nuclear-encoded gene involved in Chl biosynthesis HEMC, HEME, and PORA were also decreased when compared with the wild-type. Independent of Chl biosynthesis and photosystem, YGL8 may affect the structure and function of chloroplasts grana lamellae by regulating plastid genome encoded thylakoid membrane constitutive gene expression and indirectly influences Chl biosynthesis.

Summary: Nucleotide‐binding site–leucine‐rich repeat (NB‐LRR) resistance proteins are critical for plant resistance to pathogens; however, their mechanism of activation and signal transduction is still not well understood. We identified a mutation in an as yet uncharacterized rice coiled‐coil (CC)‐NB‐LRR, Oryza sativa RPM1‐like resistance gene 1 (OsRLR1), which leads to hypersensitive response (HR)‐like lesions on the leaf blade and broad‐range resistance to the fungal pathogen Pyricularia oryzae (syn. Magnaporthe oryzae) and the bacterial pathogen Xanthomonas oryzae pv. oryzae, together with strong growth reduction. Consistently, OsRLR1‐overexpression lines showed enhanced resistance to both pathogens. Moreover, we found that OsRLR1 mediates the defence response through direct interaction in the nucleus with the transcription factor OsWRKY19. Down‐regulation of OsWRKY19 in the rlr1 mutant compromised the HR‐like phenotype and resistance response, and largely restored plant growth. OsWRKY19 binds to the promoter of OsPR10 to activate the defence response. Taken together, our data highlight the role of a new residue involved in the NB‐LRR activation mechanism, allowing identification of a new NB‐LRR downstream signalling pathway.

Summary: To understand the molecular mechanisms of rice aerial organ development, we identified a mutant gene that caused a significant decrease in the width of aerial organs, termed ABNORMAL VASCULAR BUNDLES (AVB). Histological analysis showed that the slender aerial organs were caused by cell number reduction. In avb, the number of vascular bundles in aerial organs was reduced, whereas the area of the vascular bundles was increased. Ploidy analysis and the in situ expression patterns of histone H4 confirmed that cell proliferation was impaired during lateral primordia development, whereas procambium cells showed a greater ability to undergo cell division in avb. RNA sequencing (RNA‐seq) showed that the development process was affected in avb. Map‐based cloning and genetic complementation demonstrated that AVB encodes a land plant conserved protein with unknown functions. Our research shows that AVB is involved in the maintenance of the normal cell division pattern in lateral primordia development and that the AVB gene is required for procambium establishment following auxin signaling.

The de novo synthesis of purine nucleotides is crucial to all living organisms, but limited information is available for plants. In this study, we isolated a virescent-albino leaf 1 (val1) mutant of rice (Oryza sativa) that produces dynamic green-revertible albino and narrow-leaf phenotypes. In albino leaves, chloroplast development was defective, pigment contents were reduced, and cell division was impaired compared with the wild-type. Map-based cloning revealed that VAL1 encodes a phosphoribosylamine-glycine ligase (PurD), the second enzyme in the de novo purine biosynthesis pathway. Subcellular localization analysis demonstrated that VAL1 was localized in the chloroplast. Our results demonstrate that VAL1 is a crucial enzyme in the de novo purine biosynthesis pathway and is involved in regulating chloroplast development, chlorophyll metabolism, and cell division during leaf development in rice.