Location: Sugarbeet and Bean ResearchTitle: Phaseolus vulgaris ZIP gene family: identification, characterization, mapping and gene expression Author
Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/11/2013
Publication Date: 7/20/2013
Citation: Astudillo, C., Fernandez, A., Blair, M., Cichy, K.A. 2013. Phaseolus vulgaris ZIP gene family: identification, characterization, mapping and gene expression. Frontiers in Plant Science. 4:286. Interpretive Summary: Dry beans (Phaseolus vulgaris L) are the most highly consumed whole food legume in the world. In contrast to many other staple crops, beans are rich in a variety of nutrients, including protein, fiber, folate, and minerals. Beans are also a good source of dietary iron and zinc. An estimated two billion people suffer from iron deficiency; zinc deficiency is also widespread, with an estimated 48% of humans at risk. Biofortification of staple foods, including dry beans, with iron and zinc is one agricultural science based approach being developed and applied to combat micronutrient malnutrition. Discovery of genes involved in increased seed iron and zinc levels would be useful for biofortification efforts in beans and possibly also as targets for transgenic biofortification approach in other crops. With the recent release of the P. vulgaris genome sequence (Phaseolus vulgaris v1.0, DOE-JGI and USDA-NIFA, http:://www.phytozome.net/commonbean), it is possible to identify candidate genes for seed mineral levels. One family of genes well characterized to play a major role primarily in Zn transport and to a lesser extent Fe transport is ZIP. The Zrt and Irt -like protein (ZIP) family is well conserved among bacteria, fungi, protozoa and animals and plants. This research describes the identification and characterization of 24 members of the P. vulgaris ZIP gene family. Three members of a second family of genes bZIP transcription were also characterized similarly. They were selected specifically for their interaction with ZIP genes and involvement in Zn transport. RNA expression patterns of seven of these genes were characterized in two bean genotypes (G19833 and DOR364) with contrasting seed Zn and Fe levels under two zinc fertilization treatments. Tissue analyzed included roots and leaves at vegetative and flowering stages, and pods at 20 days after flowering. In general ZIP gene expression was upregulated in the Zn (-) fertilization treatment. The highest expression levels were in the leaves and G19833 had higher expression levels than DOR364 and also was more responsive to Zn deficiency. Three of the ZIP genes, PvZIP14, PvZIP15 and PvZIP22; and Pv bZIP1, Pv bZIP2 were located near quantitative trait loci for zinc and/or iron accumulation in seed. These results increase understanding of the role of ZIP genes in metal uptake, distribution and homeostasis in P. vulgaris and their potential importance in seed Zn accumulation.
Technical Abstract: Zinc is an essential mineral for humans and plants and is involved in many physiological and biochemical processes. In humans, Zn deficiency has been associated with retarded growth and reduction of immune response. In plants, Zn is an essential component of more than 300 enzymes including RNA polymerase, alkaline phosphatase, alcohol dehydrogenase, Cu/Zn superoxidase dismutase, and carbonic anhydrase. The accumulation of Zn in plants involves many genes and characterization of the role of these genes will be useful in biofortification. Here we report the identification and phlyogenetic and sequence characterization of the twenty three members of the ZIP (ZRT, IRT like protein) family of metal transporters and three transcription factors of the bZIP family in Phaseolus vulgaris L. Expression patterns of seven of these genes were characterized in two bean genotypes (G19833 and DOR364) under two Zn treatments. Tissue analyzed included roots and leaves at vegetative and flowering stages, and pods at 20 days after flowering. Four of the genes, PvZIP12, PvZIP13, PvZIP16, and PvbZIP1, showed differential expression based on tissue, Zn treatment, and/or genotype. PvZIP12 and PvZIP13 were both more highly expressed in G19833 than DOR364. PvZIP12 was most highly expressed in vegetative leaves of under the Zn (-) treatment. PvZIP16 was highly expressed in leaf tissue, especially leaf tissue at flowering stage grown in the Zn (-) treatment. PvbZIP1 was most highly expressed in leaf and pod tissue. The 23 PvZIP genes and three bZIP genes were mapped on the DOR364 x G19833 linkage map. PvZIP12, PvZIP13 and PvZIP18, Pv bZIP2, and Pv bZIP3 were located near QTLs for Zn accumulation in the seed. Based on the expression and mapping results, PvZIP12 is a good candidate gene for increasing seed Zn concentration.