The Mechanisms For Initiation And Development Of Axillary Buds In The Inflorescence Of Phalaenopsis

Phalaenopsis is a perennial tropical epiphytic CAM(Crassulacean acid metabolism)plant of Phalaenopsis genus in the orchid family.It is favored by people for its beautiful and colorful flowers,and long flowering period.In recent years,the Flowering regulation of Phalaenopsis is a hot topic,but the key regulatory factors for vegetative and reproductive growth of Phalaenopsis and the molecular mechanism of inflorescence development are still unclear.In the study,Phalaenopsis 'Big Chili' was used as the experimental material,and the in vivo induction and in vivo culture of the inflorescence axis axillary buds were studied by light and temperature interaction conditions.Both flower bud and leaf bud growth patterns were successfully induced.For the in vivo induction experiment,four treatments including high temperature and high light(30/28 ? day and night temperature,light intensity is 200 ?mol·m-2·s-1),high temperature and weak light(30/28 ? day and night temperature,light intensity of 30 ?mol·m-2·s-1)and low temperature and high light(24/18 ? day and night temperature,light intensity is 200 ?mol·m-2·s-1),and weak light with low temperature(24/18 ? day and night temperature,light intensity of 30 ?mol·m-2·s-1)were set according to the interaction of light and temperature to measure the physiological indexes and endogenous hormones of the axillary buds;In the in vitro Seedling culture experiment,the two treatments of high temperature with weak light(30/28 ?day and night temperature,light intensity of 30 ?mol·m-2·s-1)and low temperature with high light(24/18 ? day and night temperature,light intensity is 200 ?mol·m-2·s-1)were used to induce the axillary bud leaf bud and flower bud.In addition,the flower bud and leaf bud tissues were subjected to the transcriptome analysis,and genes related to flowering were screened and analyzed.The research results are as follows:(1)By observing the morphology and micromorphology of the inflorescence in the Phalaenopsis 'Big Chili',the suitable conditions for vegetative growth and development into complete plants were high temperature with low light(day and night temperature 30/28 ?,the light intensity is 30 and the suitable conditions for reproductive growth and development into a complete inflorescence are low temperature with high light(day and night temperature 24/18 ?,light intensity is 200 ?mol·m-2·s-1).(2)Through the analysis of the determination results of physiological indexes during the development of flower buds and leaf buds,it was found that the starch contents were increased first and then decreased while the soluble sugar contents were decreased first and then increased.The contents of sugar and starch were decreased during leaf bud differentiation.Moreover,the protein increased first and then decreased during the flower bud differentiation,it means that the protein has been accumulated a lot at the initial stage in flower bud differentiation,and then consumed at the initial stage of inflorescence primordium differentiation.However,protein was first consumed as material energy in the leaf bud,and then increased.Meanwhile,the accumulation of ZA and ABA was beneficial to flower bud differentiation,and low level of endogenous hormone GA3 should be promoted flower bud differentiation in phalaenopsis.During the whole process,the content of IAA in leaf buds was maintained at a stable low level,while the content of IAA in flower buds has been rising and was significantly higher than that in leaf buds.These results,indicate that a high level of IAA might be more conducive to the bud differentiation,and high ZA/IAA ratio,ZA/GA3 ratio,ABA/GA3 ratio may be also beneficial to the bud differentiation in Phalaenopsis.(3)In the study,186237 Transcripts and 101190 Unigene were obtained by high-throughput transcriptome sequencing.By comparing with sequences in public databases such as NR,GO,KOG and KEGG,28.19%(28,526)genes were annotated into GO database.Among them,there were 2164 significant differential genes between flower bud and leaf bud in Phalaenopsis 'Big Chili'(FDR<0.05).The significant differentially expressed genes were annotated by BLAST in the database,and the GO function was mainly enriched in 30 GO terms.The obtained genes were involved in 167 KEGG pathways,and significant enrichment in 24 pathways(P<0.05).(4)Sixteen genes related to flower formation were selected from the significantly different genes in Phalaenopsis.Among them,there were five genes related to flower development,three genes related to hormone,four genes related to response to high light intensity,and four genes related to photoperiod.The qRT-PCR analysis showed that seven genes had the highest contents at the inflorescence primordium differentiation stage.The expression level of one gene(TRINITY_DN60245_c1_g1)was the highest at the flower primordium differentiation stage.The expression levels of four genes showed the highest in the sepal primordium differentiation stage,indicating that these genes might be related to light perception.The gene(TRINITY_DN60245_c1_g1)had the highest content in the differentiation stage of petal primordia,and this gene was related to the characteristics of flower organs,belonging to the mads-box transcription factor.The expression levels of genes 5,15 and 16(RINITY_DN60907_c2_g2?TRINITY_DN60856_c0_g1?TRINITY_DN59604_c0_g3)in flower buds were significantly lower than those in leaf buds,indicating that these genes inhibited flower bud differentiation.