Tasselyzer, a machine learning method to quantify anther extrusion in maize, based on PlantCV

Male fertility in maize is controlled by development and genetic programming and is directly impacted by environmental factors such as light, temperature, water, and nutrient availability; the control of this trait has substantial agronomic utility. Maize anthers emerge from male florets, which are clustered to form the tassel at the top of the plant separated from the female ear. Quantification of anther extrusion is one important aspect in the determination of male fertility. To address the lack of an automated method to measure anther extrusion on a large scale, we developed 'Tasselyzer', a quantitative, image-based color trait analysis pipeline for tassel image segmentation, based on the existing PlantCV platform, and we applied it to determine the proportion of anther extrusion. We evaluated Tasselyzer in maize during the seven-day period of pollen shedding as well as in the temperature-sensitive male sterile mutant dcl5. With tassel images obtained with a smart phone camera, we show that the anther scores positively correlate with anther extrusion, and such methods can be used to measure environmental impacts on the dcl5 mutant. Altogether, this work establishes an automated and inexpensive method to quantify anther extrusion in maize, which would be useful for research and breeding.

Morphological characteristics and transcriptome analysis at different anther development stages of the male sterile mutant MS7–2 in Wucai (Brassica campestris L.)

Background The discovery of male sterile materials is of great significance for the development of plant fertility research. Wucai (Brassica campestris L. ssp. chinensis var. rosularis Tsen) is a variety of non-heading Chinese cabbage. There are few studies on the male sterility of wucai, and the mechanism of male sterility is not clear. In this study, the male sterile mutant MS7–2 and the wild-type fertile plant MF7–2 were studied. Results Phenotypic characteristics and cytological analysis showed that MS7–2 abortion occurred at the tetrad period. The content of related sugars in the flower buds of MS7–2 was significantly lower than that of MF7–2, and a large amount of reactive oxygen species (ROS) was accumulated. Through transcriptome sequencing of MS7–2 and MF7–2 flower buds at three different developmental stages (a–c), 2865, 3847, and 4981 differentially expressed genes were identified in MS7–2 at the flower bud development stage, stage c, and stage e, respectively, compared with MF7–2. Many of these genes were enriched in carbohydrate metabolism, phenylpropanoid metabolism, and oxidative phosphorylation, and most of them were down-regulated in MS7–2. The down-regulation of genes involved in carbohydrate and secondary metabolite synthesis as well as the accumulation of ROS in MS7–2 led to pollen abortion in MS7–2. Conclusions This study helps elucidate the mechanism of anther abortion in wucai, providing a basis for further research on the molecular regulatory mechanisms of male sterility and the screening and cloning of key genes in wucai.

Fine Mapping and Candidate Gene Analysis For A Novel Male-Sterile Mutant Ms40 in Maize

Maize male sterile mutant 40 (ms40) was obtained from the progeny of ethyl methanesulfonate (EMS) treated inbred line RP125. Genetic analysis showed that it was controlled by a single recessive nuclear gene. Cytological observation of anthers revealed that abnormal cuticles and disappearing of Ubisch bodies presented in ms40. Moreover, its tapetum exhibited delayed degradation and blocked the formation of abnormal microspore. Using map-based cloning, ms40 locus was located in a 282-kb interval on chromosome 4, five annotated genes were predicted within this region. PCR-based sequencing detected a single nonsynonymous SNP (G>A) which changed glycine (G) to arginine (A) in the seventh exon of Zm00001d053895, while no difference was found for the other four genes between ms40 and RP125. Zm00001d053895 encodes the bHLH transcription factor bHLH51 which protein was located at nuclear. Phylogenetic analysis presented that bHLH51 had the highest homology with Sb04g001650, a tapetum degeneration retardation (TDR) bHLH transcription factor in Sorghum bicolor. Co-expression analysis exposed a total of 1192 genes coexpressed with Zm00001d053895 in maize, 647 out of 1192 were anther-specific genes. In summary, these findings are conducive to the marker-assisted selection of ms40 in hybrid breeding and laid a foundation for further studies on the mechanisms of male fertility.

The SAP function in pistil development was proved by two allelic mutations in Chinese cabbage (Brassica rapa L. ssp. pekinensis)

Background Pistil development is a complicated process in plants, and female sterile mutants are ideal material for screening and cloning pistil development-related genes. Using the female sterile mutant (fsm1), BraA04g009730.3C was previously predicted as a candidate mutant gene encoding the STERILE APETALA (SAP) transcriptional regulator. In the current study, a parallel female sterile mutant (fsm2) was derived from EMS mutagenesis of a Chinese cabbage DH line ‘FT’ seeds. Results Both fsm2 and fsm1 mutant phenotypes exhibited pistil abortion and smaller floral organs. Genetic analysis indicated that the phenotype of mutant fsm2 was also controlled by a single recessive nuclear gene. Allelism testing showed that the mutated fsm1 and fsm2 genes were allelic. A single-nucleotide mutation (G-to-A) in the first exon of BraA04g009730.3C caused a missense mutation from GAA (glutamic acid) to GGA (glycine) in mutant fsm2 plants. Both allelic mutations of BraA04g009730.3C in fsm1 and fsm2 conferred the similar pistil abortion phenotype, which verified the SAP function in pistil development. To probe the mechanism of SAP-induced pistil abortion, we compared the mutant fsm1 and wild-type ‘FT’ pistil transcriptomes. Among the 3855 differentially expressed genes obtained, 29 were related to ovule development and 16 were related to organ size. Conclusion Our study clarified the function of BraA04g009730.3C and revealed that it was responsible for ovule development and organ size. These results lay a foundation to elucidate the molecular mechanism of pistil development in Chinese cabbage.