Currently I am a research scientist in Topp Lab at the Donald Danforth Plant Science Center (DDPSC) in St Louis, Mo. I have been working on crop genetics since I was a graduate student and have made some significant contributions in the field of Crop Genetics and Breeding. Crops, I said here, are wheat, rice and corn, which are the top 3 most important crops in the world, and also the top 3 most consumed grains on earth.

Research Summary

Background

Borned in China, I was getting to know the question when I was still very young, "Can we meet the growing demand for food with such a very limited resources including cropland areas"? It has turned to be a global question now with the growing population world widely. There are 7.3 billion people today according to the most recent estimate by the UN, and we may reach 9.7 billion by 2050. While food demand is expected to increase anywhere between 59% ~ 98% by 2050(a). This will shape the agricultural markets in ways we have not seen before. Farmers worldwide will need to increase crop productions, either by expanding cropland area, or by closing yield gaps and improving efficiency on existing agricultural lands through fertilizer and irrigation.

The latter relies heavily on the genetics study of mechanisms of 1) How crops per se produce bigger/better/more grains under normal conditions? 2) How crops adapt to different environments, such as low nutrient levels, heat, drought, cold and salinity. However, relatively little is known about both to date. Knowledge is extremely lack in the second point on how the hidden half, the belowground root part, affects the uptake of water and nutrients by crops, then further affects the crop productivity in the whole agricultural system. 3) Meanwhile, a third challenge arising is the grain quality as most improvements in grain yield are usually accompanied by the reduction in quality. It has been a long-standing problem for breeding community that they are able to improve either yield or quality, but almost never improve both simultaneously because of their close correlation with each other. Barely anything is known today about the black box behind the 'yield-quality' paradox.

Summary of Previous and Ongoing Research Work

My previous researches mainly focused on answering the above questions 1) and 3), while ongoing project is on question 2). Taken together, it is clear that all my researches are centered on yield/quality improvement in wheat, rice and corn.

During my graduate studies, I developed several MAS (marker assisted/aided selection) breeding pipelines, including in wheat and rice. Most importantly, my colleagues and I also explored the mechanisms underlying dense panicle and big grain in rice by cloning genes and studying their functions. In one study (b), we showed that the effect of the gene is to increase the number of grains per panicle then consequently increased grain yield by enhancing the meristem activity. This is one of the few who did the pioneer work to help set up the network between G protein and crop yield. The similar relationship was identified successively in maize and other crops after our findings. Another study of mine revealed a gene that controls grain size, shape and quality of rice (c). We found that higher expression of the rice gene OsSPL16 promoted cell division and grain filling which finally led to a bigger and better grain in rice. We also found that a loss-of function mutation of this gene was associated with the formation of a more slender grain and better quality of appearance. Finally a marker-assisted strategy, targeting alleles of the gene, which can be applied to select rice cultivars effectively and to improve grain quality and yield simultaneously was set up. Both findings have significantly advanced our understandings of molecular mechanism of 'How crops per se produce bigger/better/more grains under normal conditions?'. Both were published on Nature Genetics, which is the #1 journal in genetics. Both could also be applied into rice breeding programs, but not limited in rice because of the synteny and co-linearity among cereal crops. For example, the findings from the second example were cross validated in my corn research. By analyzing the QTL controlling the kernel size and shape in maize-teosinte (believed to be corn ancestor) introgression lines(d)(e), we found that kernel size and shape in corn are different traits under substantially independent genetic control, could have evolved independently, and could be manipulated separately in breeding programs(d). Another thing worthy to be pointed out is the materials used in corn studies really expanded maize diversity and enables the use of teosinte alleles in maize improvement, so 'they are tremendous invaluable germplasms to the whole maize community' (Ed Buckler, USDA-ARS). Besides, I have been patented twice in China (CN103243107, CN 101597610) and once in U.S.A (US20110197305 /WO2009147538).

There is no doubt that nitrogen (N) is important to crop production. Improve the Nitrogen Usage Efficiency (NUE) then undoubtedly could improve the crop yield. However, little progress has been made in this area. My ongoing project is focused on this. Funded by NSF, we try to improve corn NUE by studying its root architecture. One of the germplasms we adopted in our research is from Illinois long-term selection program which started >100 years ago. Extremely high and low nitrogen uptake lines were selected out through >100 years experiments. By comparing the high/low nitrogen uptake lines, we have picked up a few significantly important candidate genes. We currently are moving on to identify causal genes that control root growth and efficient nitrogen acquisition, which then will directly benefit corn and other crop breeders, and thus a major sector of U.S. agriculture.

Reference

a) https://hbr.org/2016/04/global-demand-for-food-is-rising-can-we-meet-it

b) Huang, X., Qian, Q., Liu, Z., Sun, H., He, S., Luo, D., ... & Fu, X. (2009). Natural variation at the DEP1 locus enhances grain yield in rice. Nature Genetics, 41(4), 494-497.

c) Wang, S., Wu, K., Yuan, Q., Liu, X., Liu, Z., Lin, X., ... & Zhang, G. (2012). Control of grain size, shape and quality by OsSPL16 in rice. Nature Genetics, 44(8), 950-954.

d) Liu, Z., Cook, J., Melia-Hancock, S., Guill, K., Bottoms, C., Garcia, A., ... & Larsson, S. (2016). Expanding maize genetic resources with predomestication alleles: Maize-teosinte introgression populations. The Plant Genome, 9(1).

e) Liu, Z., Garcia, A., McMullen, M. D., & Flint-Garcia, S. A. (2016). Genetic Analysis of Kernel Traits in Maize-Teosinte Introgression Populations. G3: Genes' Genomes' Genetics, 6(8), 2523-2530.