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. 2007 Nov-Dec;2(6):496–497. doi: 10.4161/psb.2.6.4580

AtCYT-INV1 in Arabidopsis Sugar Signaling

Zhongchang Wu 1, Xiaorong Mo 1, Ping Wu 1,✉
PMCID: PMC2634347  PMID: 19704597

Abstract

Sugar acts as a signal molecule and plays a pivotal role in plant development and stress response. Neutral/alkaline invertases found only in photosynthetic bacteria and plants is sucrose-specific enzymes cleave sucrose into glucose and fructose. We have identified a gene for neutral/alkaline invertase in Arabidopsis designated as AtCYT-INV1 which is involved in sugar/ABA signaling and plays multiple roles in plant development and osmotic stress-induced inhibition on lateral root growth.

Key Words: Arabidopsis thaliana, AtCTY-INV1, sugar signaling

Superfamily of Neutral/Alkaline Invertases

Glucose and fructose are considered as direct signal molecules, and sucrose is converted to its hexose components before it becomes the signal.1,2 In general, hexose favors cell division and expansion, whereas sucrose favors differentiation and maturation.1 Because of the pivotal role of sugar signaling on plant development and stress response, the sugar signaling pathway and its interaction with hormone signaling, especially ABA has been extensively investigated.3–9 Neutral/alkaline invertases are unique to photosynthetic bacteria and plants, and appear to be sucrose specific,10,11 while the knowledge about function of neutral/alkaline invertases is still limited. Based on BLAST search, we identified 43 full protein sequences of neutral/alkaline invertase family from 11 organisms. A phylogenetic analysis classed the proteins into five clades. The first and second clades comprise neutral/alkaline invertases from photosynthetic bacteria. Neutral/alkaline invertases of higher plants were classified into the other three clades. Nine neutral/alkaline invertases in Arabidopsis were found classed into clade III and IV. These two clades also include most of rice neutral/alkaline invertases. Two rice neutral/alkaline invertases are more closely related to photosynthetic bacteria than higher plants, which comprised clade V.

Cloning of AtCYT-INV1 which is a Member of Clade III of Nuetral/Alkaline Invertase Superfamily

We have identified a gene for neutral/alkaline invertase in Arabidopsis designated as AtCYT-INV1 using map-based cloning strategy from an EMS-generated Arabidopsis mutant insensitive to high concentrations of KNO3, KCl or mannitol repression on lateral root development. The AtCYT-INV1 cDNA includes an open reading frame (ORF) encoding a neutral invertase domain-containing protein of 551 amino acids with a predicted molecular mass of 62.8 kD. To verify whether AtCYT-INV1 can catalyze sucrose cleavage. A phylogenetic analysis using the full protein sequence revealed that AtCYT-INV1 (At 1g35580) is a member of clade III of neutral/alkaline invertase superfamily. Clade II is composed by ten genes including four genes from rice (Oryza sativa L.), five genes from Arabidopsis and one gene from lotus. The invertase domain among the ten neutral/alkaline invertase proteins is conserved. AtCYT-INV1 is closet homologous to another neutral/alkaline invertase in Arabidopsis (At4g09510) and closer to the protein from Lotus (LjIQ684K1). One neutral/alkaline invertase with conserved invertase domain as in the members of clade III in carrot (CaIQ9ZR47)10 and in Lolium (LtIO49890),12 respectively, are classed into clade IV.

AtCYT-INV1 is a Neutral Invertase and Sucrose Specific

AtCYT-INV1 mutation altered the composition of hexose and sucrose, and the concentration of glucose in Atcyt-inv1 mutant was lower than that in the WT under 3% mannitol treatment. A pH profile for the invertase activity of AtCYT-INV1 revealed that AtCYT-INV1 is catalytically active in the pH range 7–10 with optimal pH at 7.0. The Km was about 18.4 mM (y = 18.246x + 0.9927) at pH 7.0. The substrate specific to AtCYT-INV1 was determined by incubation with different sugars and the results indicate that AtCYT-INV1 enzymatic activity is sucrose specific.

AtCYT-INV1 is Involved in Sugar and ABA Signaling

Glucose can induce ABA biosynthesis.13 Glucose and ABA can restore Atcyt-inv1 mutant. The exogenous glucose, fructose or ABA can inhibit lateral root development in both the WT and Atcytinv1 mutant, while the mutant showed more sensitive to glucose, fructose or ABA inhibition than the WT. The expression patterns of the genes for ABA biosynthesis and ABA signaling responsive to mannitol, synergistic effects of mannitol and glucose or ABA were determined. The expression of ABA biosynthesis genes NCED3 and ABA35,14 in Atcyt-inv1 mutant was lower than that in the WT. The ABA responsive genes ABI3 and ABI413 were more sensitive to synergistic effects in Atcyt-inv1 mutant. The results together with that Atcyt-inv1 mutant is more sensitive to glucose and ABA in lateral root growth, indicating that ABA signaling in Atcyt-inv1 mutant is attenuated and AtCYT-INV1 is involved in sugar and ABA signaling.

Addendum to: Qi X, Wu Z, Li J, Mo X, Wu S, Chu J, Wu P. AtCYT-INV1, A Neutral Invertase, is Involved in Osmotic Stress-Induced Inhibition on Lateral Root Growth in Arabidopsis. Plant Mol Biol. 2007;64:575–587. doi: 10.1007/s11103-007-9177-4.

Footnotes

Previously published online as a Plant Signaling & Behavior E-publication: http://www.landesbioscience.com/journals/psb/article/4580

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