Relationship between hexokinase and the aquaporin PIP1 in the regulation of photosynthesis and plant growth.
Increased expression of the aquaporin NtAQP1, which is known to function as a plasmalemma channel for CO₂ and water, increases the rate of both photosynthesis and transpiration. In contrast, increased expression of Arabidopsis hexokinase1 (AtHXK1), a dual-function enzyme that mediates sugar sensing, decreases the expression of photosynthetic genes and the rate of transpiration and inhibits growth. Here, we show that AtHXK1 also decreases root and stem hydraulic conductivity and leaf mesophyll CO₂ conductance (g(m)). Due to their opposite effects on plant development and physiology, we examined the relationship between NtAQP1 and AtHXK1 at the whole-plant level using transgenic tomato plants expressing both genes simultaneously. NtAQP1 significantly improved growth and increased the transpiration rates of AtHXK1-expressing plants. Reciprocal grafting experiments indicated that this complementation occurs when both genes are expressed simultaneously in the shoot. Yet, NtAQP1 had only a marginal effect on the hydraulic conductivity of the double-transgenic plants, suggesting that the complementary effect of NtAQP1 is unrelated to shoot water transport. Rather, NtAQP1 significantly increased leaf mesophyll CO₂ conductance and enhanced the rate of photosynthesis, suggesting that NtAQP1 facilitated the growth of the double-transgenic plants by enhancing mesophyll conductance of CO₂.
Institute of Plant Sciences, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel ; The Institute of Plant Sciences and Genetics in Agriculture, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
Gilor
G
Kelly
The Institute of Plant Sciences and Genetics in Agriculture, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
Nir
N
Sade
The Institute of Plant Sciences and Genetics in Agriculture, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
Ziv
Z
Attia
Plant and Environmental Sciences, University of California Davis, Davis, California, United States of America.
Francesca
F
Secchi
Plant and Environmental Sciences, University of California Davis, Davis, California, United States of America.
Maciej
M
Zwieniecki
Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts, United States of America.
N Michele
NM
Holbrook
Institute of Agricultural Engineering, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel.
Asher
A
Levi
Institute of Agricultural Engineering, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel.
Victor
V
Alchanatis
The Institute of Plant Sciences and Genetics in Agriculture, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
Menachem
M
Moshelion
Institute of Plant Sciences, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel.
David
D
Granot
D020346:Aquaporins / Q000378:metabolism*; D017360:Arabidopsis / Q000254:growth & development* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000378:metabolism*; D001692:Biological Transport; D006593:Hexokinase / Q000378:metabolism*; D018551:Solanum lycopersicum / Q000254:growth & development / Q000378:metabolism; D010788:Photosynthesis / Q000502:physiology*; D063245:Plant Development; D018515:Plant Leaves / Q000254:growth & development / Q000378:metabolism; D018517:Plant Roots / Q000254:growth & development / Q000378:metabolism; D018547:Plant Stems / Q000254:growth & development / Q000378:metabolism; D018526:Plant Transpiration; D030821:Plants, Genetically Modified / Q000254:growth & development / Q000378:metabolism; D014026:Nicotiana / Q000254:growth & development / Q000378:metabolism; D014867:Water; D008565:Membrane Proteins
D020346:Aquaporins; D029681:Arabidopsis Proteins; D006593:Hexokinase; D014867:Water; C085550:At2g45960 protein, Arabidopsis; D008565:Membrane Proteins