DEGENERATED LEMMA (DEL) Is a New Allele of OsRDR6 That Regulates Lemma Development and Affects Rice Grain Yield

The lemma and palea are floral organ structures unique to grasses, and their development affects grain size. However, information on the molecular mechanism of lemma development is limited. In this study, we investigated a rice spikelet mutant, degenerated lemma (del), which developed florets with a slightly degenerated or rod-like lemma. The results indicate that the mutation of the DEL gene interfered with lemma development. In addition, del also showed a significant reduction in grain length and width, seed setting rate, and 1000-grain weight, which led to a reduction in yield. The results indicate that the mutation of the DEL gene further affects rice grain yield. Map-based cloning shows a single-nucleotide substitution from T to A within Os01g0527600/DEL, causing an amino acid mutation of Leu-34 to His-34 in the del mutant. DEL is an allele of OsRDR6, encoding the RNA-dependent RNA polymerase 6, and is highly expressed in the spikelet. RT-qPCR results show that the expression of some floral organ identity genes was changed, which indicates that the DEL gene regulates lemma development by modulating the expression of these genes. The present results suggest that DEL plays an important role in lemma development and rice grain yield.

The Roles of Floral Organ Genes in Regulating Rosaceae Fruit Development

The function of floral organ identity genes, APETALA1/2/3, PISTILLATA, AGAMOUS, and SEPALLATA1/2/3, in flower development is highly conserved across angiosperms. Emerging evidence shows that these genes also play important roles in the development of the fruit that originates from floral organs following pollination and fertilization. However, their roles in fruit development may vary significantly between species depending on the floral organ types contributing to the fruit tissues. Fruits of the Rosaceae family develop from different floral organ types depending on the species, for example, peach fruit flesh develops from carpellary tissues, whereas apple and strawberry fruit flesh develop from extra-carpellary tissues, the hypanthium and receptacle, respectively. In this review, we summarize recent advances in understanding floral organ gene function in Rosaceae fruit development and analyze the similarities and diversities within this family as well as between Rosaceae and the model plant species Arabidopsis and tomato. We conclude by suggesting future research opportunities using genomics resources to rapidly dissect gene function in this family of perennial plants.

MicroRNA-mediated regulation of flower development in grasses

Flower structure in grasses is very unique. There are no petals or sepals like in eudicots but instead flowers develop bract-like structures –palea and lemma. Reproductive organs are enclosed by round lodicule that not only protects reproductive organs but also play important role during flower opening. First genetic model for floral organ development was proposed 25 years ago and it was based on the research on model eudicots. Since then studies have been made to answer the question whether this model could be applicable in case of monocots. Genes from all found in eudicots classes have been also indentified in genomes of such monocots like rice, maize or barley. What’s more it seems that miRNA-mediated regulation of floral organ genes that was observed in case of Arabidopsis thaliana also has a place in monocots. MiRNA172, miRNA159, miRNA171 and miRNA396 regulate expression of floral organ identity genes in barley, rice and maize affecting various features of flower structure from formation of lemma and palea to development of reproductive organs. Model of floral development in grasses and its genetic regulation in not yet fully characterized. Further studies on both model eudicots and grasses are needed to unravel this topic. This review provides general overview of genetic model of flower organ identity specification in monocots and it’s miRNA-mediated regulation.

Phytoplasma-Induced Floral Abnormalities in Catharanthus roseus Are Associated with Phytoplasma Accumulation and Transcript Repression of Floral Organ Identity Genes

Floral symptoms caused by phytoplasma largely resemble floral reversion in other plants. Periwinkle leaf yellowing (PLY) phytoplasma and peanut witches'-broom (PnWB) phytoplasma caused different degrees of floral abnormalities on infected periwinkle plants. The PLY phytoplasma-infected plants exhibited floral discoloration, virescence, small flowers, and only occasionally full floral reversion. In contrast, PnWB phytoplasma frequently induced complete floral reversion and resulted in a witches'-broom symptom from the floral reversion. Although different degrees of floral symptoms were induced by these two phytoplasmas, the morphological disorders were similar to those of other plants carrying SEPALLATA mutations or gene silencing. Here, we compared expression levels of organ-identity-related genes and pigmentation genes during floral symptom development. Accumulation of phytoplasmas in malformed flowers and their closely surrounding leaves was also compared. In infected plants, transcript abundance of all examined organ identity genes and pigmentation genes was suppressed. Indeed, CrSEP3, a SEPALLALA3 ortholog, showed the greatest suppression among genes examined. Of the pigmentation genes, transcript reduction of chalcone synthase was most highly correlated with the loss in floral pigmentation. Floral symptom severities were associated with the accumulation of either phytoplasmas. Interestingly, both phytoplasmas accumulated to higher levels in malformed flowers than in their surrounding leaves. Many plant pathogens manipulate host plant development to their advantage. It is intriguing to see whether phytoplasmas alter floral development to increase their population.