To boost food production for a rapidly growing global population, crop yields must significantly increase. One of the avenues being recently explored is the improvement of photosynthetic capacity by installing the C4 photosynthetic pathway into C3 crops like rice to drastically increase their yield. Crops with an enhanced photosynthetic mechanism would better utilize the solar radiation that can be translated into yield. This subsequently will help in producing more grain yield, reduce water loss and increase nitrogen use efficiency especially in hot and dry environments. This review provides a summary of the factors that need to be modified in rice so that the C4 pathway can be introduced successfully. It also discusses the differences between the C3 and C4 photosynthetic pathways in terms of anatomy, biochemistry and genetics.

The specification of vascular patterning in plants has interested plant biologists for many years. In the last decade a new context has emerged for this interest. Specifically, recent proposals to engineer C4 traits into C3 plants such as rice require an understanding of how the distinctive venation pattern in the leaves of C4 plants is determined. High vein density with Kranz anatomy, whereby photosynthetic cells are arranged in encircling layers around vascular bundles, is one of the major traits that differentiate C4 species from C3 species. To identify genetic factors that specify C4 leaf anatomy, we generated ethyl methanesulfonate- and γ-ray-mutagenized populations of the C4 species sorghum (Sorghum bicolor), and screened for lines with reduced vein density. Two mutations were identified that conferred low vein density. Both mutations segregated in backcrossed F2 populations as homozygous recessive alleles. Bulk segregant analysis using next-generation sequencing revealed that, in both cases, the mutant phenotype was associated with mutations in the CYP90D2 gene, which encodes an enzyme in the brassinosteroid biosynthesis pathway. Lack of complementation in allelism tests confirmed this result. These data indicate that the brassinosteroid pathway promotes high vein density in the sorghum leaf, and suggest that differences between C4 and C3 leaf anatomy may arise in part through differential activity of this pathway in the two leaf types

Green foxtail millet (Setaria viridis) has NADP-ME type of C4 photosynthesis. Because of its short life cycle, small genome size of ~515 Mb, small plant stature, high number of seed set, simple growth requirements, and wide adaptability, this diploid (2n=18) weed is proposed to be a model species for the study of C4 photosynthesis. It is also a representative of bioenergy grasses and a model for genetic study of invasive weeds. Despite having all traits of a model species, it is difficult to cross-pollinate because its flowering behavior is not well studied. We used time lapse digital recording to study the flowering time and pattern along a single panicle. We found that flowering in Setaria was triggered by the darkness of the night and when the temperature was lower than 35°C. The anthesis of all the spikelets in a panicle took up-to three nights flowering from 9:30 pm to 10:00 am in the morning. Each spikelet has three phases of anthesis during which pollination occurs. A spikelet remains open for less than three hours. The pollination time for each spikelet is less than 60 minutes. Information from this study will facilitate the geneticists and plant breeders to plan for efficient crossing of Setaria.

An efficient method for crossing green foxtail (Setaria viridis) is currently lacking. S. viridis is considered to be the new model plant for the study of C4 system in monocots and so an effective crossing protocol is urgently needed. S. viridis is a small grass with C4-NADP (ME) type of photosynthesis and has the advantage of having small genome of about 515 Mb, small plant stature, short life cycle, multiple tillers, and profuse seed set, and hence is an ideal model species for research. The objectives of this project were to develop efficient methods of emasculation and pollination, and to speed up generation advancement. We assessed the response of S. viridis flowers to hot water treatment (48°C) and to different concentrations of gibberellic acid, abscisic acid, maleic hydrazide (MH), and kinetin. We found that 500 μM of MH was effective in the emasculation of S. viridis, whilst still retaining the receptivity of the stigma to pollination. We also report effective ways to accelerate the breeding cycle of S. viridis for research through the germination of mature as well as immature seeds in optimized culture media. We believe these findings will be of great interest to researchers using Setaria.