Wreaths by the thousands: finding the non-typical in leaf anatomy of activation-tagged rice lines

Rice is a major staple for human consumption more than any other crop and increase in its yield would help cope with the world's escalating population. However, it utilizes C3 photosynthesis, which is less efficient than that of C4 photosynthesis. It is the aim of the C4 Rice Project to identify genes associated with C4 properties and test the feasibility of introducing these into rice. To track these genes of interest, one of the various activities employed is the large-scale anatomical screening of rice mutant; or the activation-tagged rice lines. This population has been generated through the use of transposable elements randomly inserted into the genome, thereby creating increased expression or knock-out of specific genes. Activation-tagged rice lines may have altered leaf anatomical phenotype for emergence of C4 properties particularly the distinct wreath-like appearance of their cells known as Kranz anatomy and denser vascular system. To find changes in the leaf anatomy denotes that introduced components of the C4 cycle into the rice genome had an impact on leaf development. At IRRI, a total of 14,462 activation-tagged rice lines from Korea and Taiwan were screened for changes in leaf vein density. Forty-seven lines were found to have increase in number of veins per unit leaf width compared to wildtypes Dongjinbyeo, Hwayoung and Tainung-67. These lines were further evaluated for other traits including vein dimensions, leaf thickness, and mesophyll and bundle sheath cell number and size that may be associated to the increase in vein number. Seeds of these lines were requested from Academia Sinica (Taiwan) and from Kyung Hee University (Korea) to grow in IRRI. Thus for 2011 screening 36% had been found to retain this phenotype after advancing to the second generation.