Preliminary Study On Radish In Response To High And Low Temperature

Radish is a crucial root vegetable crop of Brassicaceae family with many varieties and large cultivated area in China.At the same time,radish is a kind of low-temperature and long-day crop.In actual production,there are few heat-tolerant radish varieties and few studies on genes related to high temperature stress.On the other hand,low temperature can induce flower bud differentiation and transfer from vegetative growth to reproductive growth,which affects the yield and quality of radish taproot,but little is known about the molecular mechanism of vernalization on the development of radish taproot.In this study,physiological detection,paraffin section observation and transcriptome sequencing analysis were used to explore the developmental characteristics of radish taproot and its preliminary response mechanism to high and low temperature.The experimental results are as follows:1.The "Huoche" radish with certain heat tolerance was treated at 40 ℃,and some physiological parameter changes of young leaves under short-term heat stress were detected.Furthermore,we acquired 1802 differentially expressed m RNAs(including encoding some heat shock proteins,heat shock factor and heat shock-related transcription factors),169 differentially expressed lnc RNAs,3 differentially expressed circ RNAs and 10 differentially expressed mi RNAs by whole transcriptome sequencing.Through function prediction and enrichment analysis,our results suggested that the significantly possible pathways /complexes related to heat stress in radish leaves were circadian rhythm-plant,photosynthesis-antenna proteins,photosynthesis,carbon fixation in photosynthetic organisms,arginine and proline metabolism,oxidative phosphorylation,peroxisome and plant hormone signal transduction.Besides,we identified one lnc RNA–mi RNA–m RNAs combination responsive to heat stress.2.The paraffin section of the fleshy taproot’s cross section in "Sanchi" and "Huoche" radish cultivars showed symmetrical growth rather than actinomorphic growth in the stele tissue of the true root and the neck of the radish root,and the growth of the stele tissue accelerated after the 15 th day of growth,resulting in the flattening of epidermis and cortical cells that could not divide.Through the analysis of the characteristics of fleshy taproot development of these two radish varieties at different developmental stages,it was found that the thickening rate of fleshy taproot was not obvious in the early stage of development,but accelerated obviously after "belly breaking" on the 35 th day of growth.And then the cold-resistant "Sanchi" radish was treated with low temperature vernalization at 4 ℃ for 21 days.Compared with the control group,vernalization significantly promoted flower bud differentiation,bolting and flowering of radish,bolting on the 15 th day after vernalization and flowering on the 30 th day.In the control group,the fleshy taproots of radish were mature on the 70 th day of growth,while vernalization significantly inhibited the growth of fleshy taproots and almost did not thicken.At the same time,the results of paraffin section showed that the development rate of stele tissue of taproot of vernalization group slowed down obviously after 20 days of growth.Through whole transcriptome sequencing analysis,211 to 1922 differentially expressed genes(including some FLC,SOC1 and FT genes),32 to 74 differentially expressed lnc RNAs,18 to 26 differentially expressed circ RNAs,and 1 to 12 differentially expressed mi RNAs were detected.Through enrichment analysis,the pathways related to the effect of low-temperature vernalization to radish taproot were plant hormone signal transduction and circadian rhythm-plant pathways.At the same time,we also constructed four ce RNA regulatory networks related to the response of low-temperature vernalization.These results are helpful to further clarify the developmental mechanism of radish taproot,explore the molecular regulatory network of radish response to high and low temperature,and provide relevant data for breeding radish with bolting and high temperature tolerance.