title: The existence of C4-bundle-sheath-like photosynthesis in the mid-vein of C3 rice.
abstract: BACKGROUND
  Recent studies have shown that C4-like photosynthetic pathways partly reside in photosynthetic cells surrounding the vascular system of C3 dicots. However, it is still unclear whether this is the case in C3 monocots, especially at the molecular level.
  
  
  RESULTS
  In order to fill this gap, we investigated several characteristics required for C4 photosynthesis, including C4 pathway enzymes, cyclic/non-cyclic photophosphorylation rates, the levels and assembly state of photosynthetic machineries, in the mid-veins of C3 monocots rice with leaf laminae used as controls. The signature of photosystem photochemistry was also recorded via non-invasive chlorophyll a fluorescence and reflectance changes at 820 nm in vivo. Our results showed that rice mid-veins were photosynthetically active with higher levels of three C4 decarboxylases. Meanwhile, the linear electron transport chain was blocked in mid-veins due to the selective loss of dysfunctional photosystem II subunits. However, photosystem I was sufficient to support cyclic electron flow in mid-veins, reminiscent of the bundle sheath in C4 plants.
  
  
  CONCLUSIONS
  The photosynthetic attributes required for C4 photosynthesis were identified for the first time in the monocotyledon model crop rice, suggesting that this is likely a general innate characteristic of C3 plants which might be preconditioned for the C4 pathway evolution. Understanding these attributes would provide a base for improved strategies for engineering C4 photosynthetic pathways into rice.
authors.affiliation: College of Life Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing, 210023, China.
authors.forename: Weijun
authors.initials: W
authors.lastname: Shen
authors.affiliation: College of Life Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing, 210023, China.
authors.forename: Luhuan
authors.initials: L
authors.lastname: Ye
authors.affiliation: College of Life Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing, 210023, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Ma
authors.affiliation: College of Life Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing, 210023, China.
authors.forename: Zhongyuan
authors.initials: Z
authors.lastname: Yuan
authors.affiliation: College of Life Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing, 210023, China.
authors.forename: Baogang
authors.initials: B
authors.lastname: Zheng
authors.affiliation: Institute of Food and Crops, Jiangsu Academy of Agricultural Sciences, 50 Zhongling Street, Nanjing, 210014, China.
authors.forename: Chuangen
authors.initials: C
authors.lastname: Lv
authors.affiliation: College of Life Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing, 210023, China.
authors.forename: Ziqiang
authors.initials: Z
authors.lastname: Zhu
authors.affiliation: University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA.
authors.forename: Xiang
authors.initials: X
authors.lastname: Chen
authors.affiliation: College of Life Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing, 210023, China. 1053803594@qq.com.
authors.forename: Zhiping
authors.initials: Z
authors.lastname: Gao
authors.affiliation: College of Life Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing, 210023, China. gxchen@njnu.edu.cn.
authors.forename: Guoxiang
authors.initials: G
authors.lastname: Chen
keywords: C3 and C4 photosynthesis; Cyclic/linear electron flow; Dysfunctional PSII; Mid-vein; Rice