Jian-Chun Guo1*, Yuan Yao1, Meng-Ting Geng1, Rui-Mei Li1, Jiao Liu1, and Shao-Ping Fu1

Jian-Chun Guo1*, Yuan Yao1, Meng-Ting Geng1, Rui-Mei Li1, Jiao Liu1, and Shao-Ping Fu1

The researches on the invertase family genes and the role on starch accumulation in Cassava (ManihotesculentaCrantz)

Jian-Chun Guo1*, Yuan Yao1, Meng-Ting Geng1, Rui-Mei Li1, Jiao Liu1, and Shao-Ping Fu1

1)Key Laboratory of Biology and Genetic Resources of Tropical Crops, Ministry of Agriculture, Institute of Tropical Bioscience and Biotechnology, Chinese Academy of Tropical Agricultural Sciences, 571101 Haikou, China;

* , Registrant ID# 2164

In higher plants, sucrose is main form of photoassimilation for transportation, in which the sucrose metabolizing enzymes play a very important role. The invertases irreversibly decompose sucrose into glucose and fructose; meanwhile function in phloem unloading, plant growth, flowering, and signal transduction, in response to biotic and abiotic stresses and so on. The invertases have many forms of isozymes, which function in photosynthesis regulation in source organs, and sink strength building in sink organs. Thus, the researches on cassava invertase gene family evolution, expression characteristics and functions can help to understand the relationship between the "source" and "sink" during the process of cassava root starch accumulation.

The analysis of the total activity of invertase in cassava were found that lower activity of invertase in leaves is benefit to starch accumulation in roots, and higher activity of invertase in root phloem is benefit to starch accumulation in roots. The activity of cell wall invertase was lower than that of vacuolar invertase and neutral / alkaline invertase activity in tuber, which indicates that the unloading sucrose into sink cells probably mainly through plasmodesma or sucrose transporter protein in cassava.

Based on the information of cassava genome database, 20 cassava invertase family genes were cloned from cassava variety(ManihotesculentaCrantz SC8), which include six cell wall invertases (named MeCWINV1-6, GenBank: JQ339929, JX291160, JN801147, JQ792172, JX291159, JQ339930); three vacuolar invertaes (named MeVINV1-3, GenBank: JX291158, JQ792174, JQ792173); and 11 neutral / alkaline invertases (named MeNINV1-10, nINVI)GenBank: JN616390, JQ339931, JQ339932, JQ782220, KF533729, KF533730, JN801148, JQ339933, KF533731, KF533732, DQ138370). α group members of neutral / alkaline invertases locate in organelles of plastids α1 (MeNINV6,8, 9), and in mitochondria or plastids α2 (MeNINV1,7, 10), the β group members of neutral / alkaline invertases (MeNINV2,3, 4, 5,nINVI ) locate in the cytoplasm.

Based on phylogenetic analysis, subcellular localization, intron - exon and genome structure information, it is deduced that cassava acid invertasegenes evolved from an original gene, which firstly evolved to three initial genes of MeCWINV1, MeCWINV2,6 and MeVINV1,2,3. MeCWINV1 replicated once to form MeCWINV3, and then continually replicated once more to evolve MeCWINV4. The initial geneof MeCWINV2, 6 replicated once to form MeCWINV2 and MeCWINV6, and MeCWINV2tandemly replicated to form MeCWINV5. The original gene of MeVINV1,2,3 was added a vacuolar signal sequence at the N-terminal protein during evolution to form the vacuolar invertase initial gene, which replicated once to form MeVINV3 and MeVINV1, and the MeVINV1 replicated once more to form MeVINV2. α1 and α2 subgroups of Cassava neutral / alkaline invertase genes evolved form the respectively initial genes of MeNINV6,8 and MeNINV1,7. The initial gene of MeNINV6,8replicated once to form MeNINV6 and MeNINV8, and the MeNINV8 replicated once more to form MeNINV9; the initial gene of MeNINV1, 7 replicated once to form MeNINV1 and MeNINV7, and the MeNINV7 replicated once more to form MeNINV10. The original gene evolved into β groupinitial genes of MeNINV4, MeNINV5 and MeNINV2, 3. The initial gene of MeNINV4 replicated once to form nINV1, the initial gene of MeNINV2, 3 replicated once to MeNINV2 and MeNINV3.

The differential expression analysis of the cassava invertase genes in tissues and organs found that: the activity of MeCWINV1 and 3 were higher than other MeCWINVs in leaves and tubers, which suggested that sucrose was mainly catalyzed by the MeCWINV1 and 3 in the apoplastic space of cassava source and sink organs. All MeVINVs are highly expressed in leaves, while only MeVINV1 and 2 are highly expressed in tubers at cassava tuber maturity stage. Thus, MeVINV1 and 2play an important role in sucrose unloading and starch accumulation; MeNINV1, 6, 10, and nINV1 are strongly expressed in source tissues (leaves), and MeNINV1 and nINV1 also play an important role in sink organs (tuber).

Key words: Cassava; invertases; evolution; profit expression.