Piriformospora Indica Enhanced Root Rot Resistance Of Gerbera By Regulating PAL And POD

Gerbera jamesonii Bolus(also known as African daisy),originated from South of Africa,is an herbaceous perennial-root flower belonging to gerbera genus.It is one of the five major fresh cut flowers in the world.Recently,along with the expansion of its planting area,gerbera industry faced increasing serious plant diseases and pests,among which root rot was one of the main diseases.Due to its wide distribution and severe damages it caused,root rot has seriously affected the quality and yield of gerbera cut flower industry,leading to large economic losses.Therefore,the prevention and control of root rot has been regarded as one of the problems that need urgent solution.Fujian province is an important gerbera producing area in China.Over the last few years,the areasuffered from serious root rot damages,which have sternly hampered the healthy development of the gerbera industry in the area.Phenylalanine ammonia lyase is the key enzyme and rate-limiting enzyme of phenylalanine metabolism pathways andis of great significance during the growth and development progress and the stress-resistance and defense responses of plants.It is oftentimes taken as a key index to measure the stress resistance of plants.Peroxidase is a kind of oxidase commonly found in plants and animals and microorganisms,which played a vital role in the promotion of plant growth and development,the improvement of plants’disease resistance and other aspects.Piriformospora indica is a mycorrhiza-like fungus,whose roles in the promotion of plant growth and the enhancement of plant stress resistance have been widely proved in many plant species.In our previous study,we found that the colonization of P.indica could promote the rooting and growth of gerbera after multiple continuous sub-culturing,and could improve the root rot resistance of the seedlings of "Shuifen"(a variety of Gerbera jamesonii Bolus).Our current study aimed to investigate the effects of the colonization of P.indica on the growth and disease resistance of‘Linglong’gerbera through the following aspects:comparing the growth and root rot resistance of the tissue cultured and transplanted plantlets of ’Linglong’ with or without P.indica colonization,analyzing the disease resistance,antioxidant enzyme activities and the expression of PAL and POD genes in the transplanted seedlings of Gerbera.The results were listed as follows:1.By using tissue-cultured ’Linglong’ Gerbera plantlets,we studied the effects of P.indica on the plant height,leaf number,root length and number,transplant survival rate of the tissue culture plantlets,and the weight and length of the aboveground and underground parts of transplanted seedlings.Results showed that P.indica improved the growth and transplant survival rate of tissue cultured gerbera plantlets,whichsignificantly promoted the growth of underground parts of transplanted plantlets,indicating that P.indica can promote the growth of gerbera.2.Using tissue cultured transplanted plantlets of ’linglong’,we studied the difference of symptom on the groups with/without P.indica colonization under the Phytophthora cryptogea treatment.It was found that the pathogen growth was inhibited about 3 days when P.indica existed.And the tissue cultured plantlets without P.indica infection died in 10 days post pathogen infection,while the plantlets with P.indica infection showed better upright growth although their leaves also turned yellow.For the transplanted plants,the leaves of the control group began to appear wilting on the 2nd day of P.cryptogea treatment,and the plants died of wilting on the 6th day,while the gerbera colonized by P.indica grew well.It is speculated that P.indica colonization could effectively promote the root rot resistance of gerbera.3.We studied the changes of antioxidant enzymes activities in roots with/without P.indica colonization before and after inoculation of P.cryptogea.Results revealed that gerbera roots with P.indica colonization presented higher PAL and other antioxidant enzymes activities than the controls.Both P.indica and P.cryptogea induced the increase of PAL and POD enzyme activities,but the induction of POD caused by P.indica was slightly lower than P.cryptogea.Co-culture experiments showed that P.indica had no direct antagonistic effect on P.cryptogea,which indicated that the possible mechanism of P.indica in improving the root rot resistance of gerbera by enhancing the activity of PAL and other antioxidant enzymes in gerbera.4.We cloned four PAL genes and studied the change of the PAL gene expressions under different stresses,using the real-time quantitative PCR technology.The results showed that GjPAL3 was induced by various stresses.However GjPAL2 expression was widely inhibited,and not clustered with other PAL genes,indicating that GjPAL2 differs greatly from the others.However,the expression patterns of GjPALl and GjPAL4 were most similar.In addition,the expression of GjPAL1,GjPAL3 and GjPAL4 was significantly induced by P.cryptogea and positively correlated with PAL enzyme activity,indicating that it plays an important role in the response to gerbera root rot.5.Through cloning,we obtained 4 of POD genes.The result showed that these geneexpressions and POD activities were all found to be significantly or very significantly influenced by different treatments.And,the expression pattern of GjPOD4 differed from other GjPODs.Correlation analysis showed that the expression of GjPOD42 was significantly positive correlated with POD activity in different organs(P<0.05).Notably,all of the gene expressions were significantly induced and positively correlated with the POD activities under the P.cryptogea treatment.The results obtained in this study indicated that GjPODs played an important role in the stress responses of gerbera,especially during the gerbera-P.cryptogea interaction.And,the function of GjPOD4 might differ from other GjPODs6.qRT-PCR results showed that P.cryptogea infection influenced the expressions of PALs and PODs in roots that were pre-inoculated with or without P.indica.And that the expressions of PAL and POD differed significantly between gerbera with and without P.indica colonization.It is speculated that P.indica may increase the root rot resistance of gerbera through regulating the expressions of PAL and POD genes.