The Role Of Multifunctional Protein MAP18/PCaP2 In Arabidopsis Thaliana Under Cold Stress

Cold stress affects the growth of plants and crop productivity.It's very important to study the mechanism of cold stress and chilling tolerance in plants.Previous studies have shown that the regulatory mechanisms of plants adapting to cold stress include C-repeat binding factor-cold-responsive gene?CBF-COR?signaling regulation and hormone-dependent abscisic acid?ABA?-based molecular regulation.At present,Arabidopsis plasma membrane-associated Ca²⁺-binding protein-2?PCaP2?,also known as microtubule-associated protein 18?MAP18?,which regulates the dynamic of microtubules depolymerization and F-actin severing,and is involved in the regulation of ABA signaling pathways.PCaP2 widely expressed in roots,hypocotyls,flowers and cotyledons.Studies have reported that the expression of PCaP2 is 8 times higher than that of other stress or hormone stimulation under cold stress.However,the molecular mechanism of PCaP2 in plant hypothermia is still unclear.In this research,Arabidopsis thaliana wild type plants?WT?,PCaP2 overexpression?PCaP2-OE?,mutant?pcap2?and PCaP2-RNAi transgenic plants were used.Firstly,we examined the expression of PCaP2 in Arabidopsis thaliana under cold stress.Then,observed and analysised the growth of Arabidopsis thaliana WT,PCaP2-OE,pcap2 and PCaP2-RNAi plants.Meanwile,examined the expressions of genes related to cold stress,In addition,explored the role of PCaP2 microtubule destabilization and F-actin severing activity under cold stress.Finally,investigated the role of PCaP2 in crosstalk of cold stress and ABA signal transduction,to revealed the function of PCaP2 in cold stress.The main results are as follows:1.Under cold stress,the expression of PCaP2 in Arabidopsis increased significantly.Under normal conditions?22??,PCaP2 was mainly expressed in cotyledons,hypocotyls,lateral roots and main roots,and hardly expressed in true leaves.Under cold stress?4??,the expression of PCaP2 significantly increased in cotyledons,true leaves,hypocotyls,lateral roots and main roots.The expression of PCaP2 in cotyledons,ture leaves,hypocotyls and roots reached the peak at 3 h under cold stress treated.2.Normal conditions?22??,the germination rates and growth of WT,PCaP2-OE,pcap2 and PCaP2-RNAi were not significantly different.Under cold stress?14??,the germination rates,the root length,lateral root numbers and leaf area of WT,PCaP2-OE,pcap2 and PCaP2-RNAi were significantly different.Compared with WT,pcap2 mutant plants showed shorter root length,fewer lateral root number and smaller leaf area,and germination rate was significant inhibited after 1 d treatment under cold stress.3.Under cold stress?4??,the expression levels of cold-response genes CBF1,CBF3,KIN1,KIN2,RD29A,COR15B and HAB1 in PCaP2-OE plants were significantly increased,while in pcap2 nutant plants the expression were inhibited.4.Under normal condition?22??,microtubule depolymerization treatment had no significant effect on the growth of Arabidopsis WT,PCaP2-OE,pcap2 and PCaP2-RNAi.Under cold stress?14??,after treatment with microtubule depolymerization agents,WT,PCaP2-OE,pcap2 and PCaP2-RNAi plants showed longer root length,more lateral root number and larger leaf area.5.After treatment with microtubule depolymerization agents,the expression levels of cold-response genes CBF1,CBF2,CBF3,KIN1,KIN2,COR15B and HAB1 in PCaP2-OE plants were significantly increased,while in pcap2 plants the expressions of these genes were inhibited.6.Under normal conditions?22??,the growth of WT,m1?loss of point mutation of microfilament activity 1?,m2?loss of point mutation of microfilament activity 2?,m7?control point mutant 7?and PCaP2-RNAi plants didn't show significant difference.Under cold stress?14??,the growth of WT,m1,m2 and m7 plants had no significant difference.But,the root length,lateral root number,and leaf area of PCaP2-RNAi plants were significantly lower than those of wild type plants.7.Under cold stress,the expressions of ABA-response genes SnRK2.2,SnRK2.3,ABF2,KIN1,KIN2 and RD29A in PCaP2-OE plants significantly increased,the expressions of SnRK2.6,ABF1,ABF3 and ABF4 in PCaP2-OE plants were inhibited.Under ABA treatment,the expression levels of cold-response genes CBF1,CBF3,KIN1,KIN2,RD29A,COR15B and HAB1 in PCaP2-OE plants were significantly increased,while in pcap2 plants the expression were inhibited.In summary,cold stress induced PCaP2 expression up-regulation in Arabidopsis.PCaP2enhances the adaptability of Arabidopsis to cold stress by participating in the regulation of the expression of cold-response genes and ABA-response genes.In addition,the microtubule destabilization of PCaP2 plays a role in the plant's resistance to cold stress,whereas the F-actin severing activity of PCaP2 doesn't play a role in plant adaptation to cold stress.Therefore,PCaP2 plays an important role in plants adapting to cold stress and plays a role in the interaction of cold stress signals and ABA signals.