The Mechanism Of Ginger Rhizome Formation And Enlargement

Ginger(Zingiber officinale Rosc.),its edible organ is underground metamorphic rhizome.Its size is not only a measure of the level of yield,but also an important indicator of appearance commodities.Clarifying the development mechanism of ginger rhizome can provide theoretical support for cultivation technology innovation and germplasm creation.Therefore,based on the observation of the anatomical structure of the rhizome formation process,targeted metabolomics were used to study the changes of endogenous hormones in the ginger rhizome formation process.Differentially expressed genes were analyzed through transcriptome sequencing.The functions of ZoABF4 and ZoSUT2 genes have been verified.At the same time,we studied the relationship between rhizome enlargement and endogenous hormones,sugar metabolism,etc.,taking the effect of sowing depth on the enlargement of ginger rhizomes as the starting point.The main findings are as follows:(1)The formation of new ginger rhizomes began during the germination of ginger buds.There was a preliminary shoot tip structure during the bud germination period,with active meristematic cells,but no obvious rhizome and vascular bundles were found.During the rhizome formation period,typical shoot tip and rhizome structure could be observed,growth cone and leaf primordium cells were active,pith cells tended to mature,and vascular bundle development was completed.(2)During the formation of ginger new rhizomes,the contents of IAA,ABA and JA gradually increased,while the contents of GA1,GA4,GA7,zeatin,trans-zeatin nucleoside,IP and IPR gradually decreased.The content of ACC was higher before the buds germinate,and the content was very low during the buds germinate.The isoleucine jasmonic acid content increased first and then decreases with ginger germination.It can be seen that different plant hormones play different roles in the process of ginger bud germination,rhizome induction and rhizome formation.GA and ethylene can promote the germination of ginger,JA and ABA can induce rhizome formation,ABA and IAA can promote rhizome formation,while GA is not conducive to rhizome formation.When ginger rhizomes enlargement,the contents of IAA and ABA gradually increased,and the contents of GA3 and zeatin gradually decreased.(3)During the formation of ginger rhizomes,the expressions of related genes involved in the biosynthesis of IAA,ABA,BR and JA were up-regulated;while the related genes involved in the biosynthesis of CTK and GA were significantly down-regulated,and the expressions of CKX and GA2ox,which catalyze their decomposition,were significantly up-regulated.The changes of plant hormones in new rhizomes were consistent.IAA could directly mediate the expression of AUX/IAA and GH3 genes and promote the signal response of IAA;while the down-regulated expression of CRE1,AHP and B-ARR reduced the sensitivity of ginger to CTK;The down-regulated expression of transcription factor(TF)in response to GAs weakened the signal transduction of GA,while ABA promoted the expression of Sn RK2 and ABF,and promoted the expression of downstream genes of ABA.Both JA and BR promoted gene expression in their process of signal transduction.(4)During the ginger rhizomes enlargement,compared with the sowing depth of 2 cm,the sowing depth of 10 cm significantly promoted the enlargement of new rhizomes,the fresh rhizome weight increased by 91.34%,and the root length,root surface area and root vitality increased by 62.27%,44.2%and 17.34%,respectively.Sowing depth of 10 cm significantly increased IAA and ETH content,and reduced ABA and CTK content of root.At the same time,the expression of ARF7,LBD16 and PIN1 genes was significantly increased,while the expression of AUX/IAA was significantly reduced.The promoting effect of sowing depth of10 cm on the enlargement of ginger rhizomes is also related to the up-regulation of aquaporin gene expression,together with the vigorous development of vascular bundles,which promoted the conduction and accumulation of water in ginger.Sowing depth of 10 cm increased the activities of rhizosphere invertase,amylase,protease,dehydrogenase and polyphenol oxidase,increased the abundance of Acidobacteria,Gemmatimonadetes and Planctomycetes,and promoted the expression of nar G,nir S,nif H and amo A genes,which was conducive to maintaining better rhizosphere nutrition.(5)During the ginger rhizomes enlargement,sowing depth of 10 cm significantly increased the net photosynthetic rate,stomatal conductance,intercellular CO₂ concentration and transpiration rate of ginger leaves,as well as Rubisco and FBPase activity and gene expression levels.Compared with sowing depth of 2 cm,sowing depth of 10 cm significantly increased the photosynthetic electron transfer efficiency of ginger leaves and reduced heat dissipation.Sowing depth of 10 cm promoted the gene expression of sucrose transporters(SUTs and SWEETs),improved the loading and unloading efficiency of sucrose,reduced the activity of D-SUS and CWINV and the gene expression level in leaves,and increased the enzyme activity and gene expression in rhizomes,which showed that the sucrose loading in the leaves and the unloading in the rhizomes were promoted,and the sucrose concentration gradient between the sink and the source was increased.Sowing depth of 10 cm also increased the expression levels of starch synthesis related genes(SSS,BE,PGE and AGPase),decreased the expression of starch decomposition related genes(?-AM,?-AM and SP)in ginger rhizomes,and promoted the synthesis and accumulation of starch in ginger rhizomes.(6)The expression levels of ZoABF4 and ZoSUT2 were significantly increased with the formation and enlargement of ginger rhizomes,and the expression of ZoABF4 in the ginger mutant was significantly reduced.Gene cloning and functional analysis showed that ZoABF4is located in the nucleus,and ZoSUT2 is located in the cell membrane.The ZoSUT2 promoter has three ABRE cis-acting elements.Y1H proved that ZoABF4 had a transcriptional regulatory effect on the SUT2-3 promoter region of ZoSUT2.Dual luciferase experiments showed that ZoABF4 activated ZoSUT2 transcription.