Different Strategies Adapted By Two Cassava Cultivars In Response To Drought

Cassava is one of the most drought-tolerant crops,however,the underlying mechanism for its ability to survive and produce under drought remains obscure.The paper selected Southern China 124(SC124)and Argentina 7(Arg7).Two cassava cultivars,SC124 and Arg7,were planted a pot and treated by gradually reducing the soil water content.Their responses to the drought stress were examined through their morphological and physiological traits and proteomic analysis.SC124 plants adapted a ‘survival’ mode under mild drought stress as evidenced by early stomatal closure and leaf wilt,and increase of osmotic adjustment substances and antioxidant activity,and a reduction of photosynthetic capacity,resulting in early growth quiescence.In contrast,Arg7 plants underwent senescence of older leaves but continued to grow,although at a reduced rate,under mild drought.SC124 plants were more capable of surviving prolonged severe drought than Arg7.The isobaric tags for relative and absolute quantitation(iTRAQ)identified over5445 proteins which were higher than those of other plants.A total of 3765 proteins were identified in the leaves.There were 561 differential proteins in the two cultivars.There were 523 differential proteins in SC124 which were obviously more than 208 in Arg7.The result showed that the response of SC124 leaves to drought were faster than that of Arg7 leaves.Some proteins related to photosynthesis and basic metabolism reduced significantly under mild drought,and reduced more in SC124 than in Arg7.The results were consistent with the results of phenotypic and physiological traits.A total of 4382 proteins were identified in the roots,and the number was slightly more than that of the leaves.However,there were only 129 differential proteins in the two cultivars,80 of them were up-regulated and 49 were down-regulated.The result that 103 differental peoteins in Arg7 were more than 51 in SC124 was opposite to leaves.Comparison of drought and rewatering for 24 h showed that the response to rewatering was very little.14 proteins in Arg7 were found to be down-regulated,but no up-regulated protein was found.In SC124,10 proteins were up-regulated and 23 proteins were down-regulated.The result suggested that SC124 was more responsive to rewatering than Arg7.The drought-responsive proteins identified in the study were an aquaporin,myo-inositol 1-phosphate synthases,and a number of proteins involved in the antioxidant systems and secondary metabolism and many proteins that might play a role in signalling or gene regulation which included several protein kinases,two14-3-3 proteins,several RNA binding proteins and transcription factors,and two histone deacetylases.It was noteworthy that the proteins related to the synthesis of linamarin were significantly increased under drought,such as UGT85K4 and CYP71 E increased in the two varieties roots,while the protein related linamarin degradation in leaves and roots were significantly reduced.The content of linamarin increased significantly in SC124 leaves and Arg7 roots under drought.The results also support the notion that linamarin might play a role in cassava to drought.15 proteins were selected and analyzed their expression at the transcriptional level by quantitative real time PCR(q RT-PCR).The results showed that the variation of 9was consistent with that of the proteome.Me UGT85K4,Me HDAC and Me WHX gene was cloned from SC124.Me UGT85K4 gene had a full-length c DNA of 1452 bp.Me UGT85K4 was localized in the cell membrane and nucleus.Me HDAC gene had a full-length c DNA of 939 bp.Me WHX gene had a full-length c DNA of 741 bp.Me HDAC and Me WHN were localized in the cell nucleus.The over-expression vector and the interference expression vector were constructed.At present,transgenic Arabidopsis thaliana with Me HDAC gene was obtained.Overexpression of Me HDAC gene enhanced ABA tolerance although Me HDAC gene was induced to expression during salt,ABA and drought.This research showed that two cassava varieties had different strategies in response to drought.SC124 protect membrane intact of leaves and roots by reducing of photosynthesis and basal metabolism proteins and increasing drought-resistant proteins to result in wilting of leaves and reducing the loss of water,and Arg7 continued to grow as far as possible by increasing drought-resistant proteins in the roots to absorb more water,but it hurt cell membrane of roots and leaves.SC124 is suitable for planting in dry areas and can survive for a long time,and Arg7 is suitable for planting in intermittent arid regions and can obtain higher yields.