Phenotypic Identification And Transcriptomic Analysis Of Thecreeping Tartary Buckwheat（Fagopyrum Tataricum） Mutant Lazy1

Gravity is known as an important environmental factor involved in the regulation of plant architecture.To identify genes related to the gravitropism of Tartary buckwheat,a creeping line lazy1 from the mutant bank by ⁶⁰Co-γray radiation was selected to study the physiological characteristics and key gene functions.The main research results are as follows:（1）Genetic analysis indicated that the creeping phenotype of lazy1 was attributed to a single recessive locus.（2）The horizontal and inverted suspension experiments of lazy1mutant showed that the main stem angle of lazy1 mutant rarely changed.The creeping growth phenotype of lazy1 mutant was not recovered by spraying exogenous heteroauxin,hormodin,α-rhodofifix,and gibberellin,which indicated that lazy1 was completely lacking in shoot negative gravitropism.（3）Cytological observation showed that,different from the well-organized and equivalent cell elongation of wild type（WT）,lazy1exhibited dilated,distorted,and abnormally arranged cells in the bending stem.（4）There was no significant difference of indole-3-acetic acid（IAA）levels was found between the far-ground and near-ground bending sides in lazy1,which suggests that the asymmetric cell elongation of lazy1 was not induced by auxin gradient.However,significantly increased of GA₃level was found between the far-ground and near-ground bending sides in lazy1.Meanwhile,lazy1 showed up-expressed gibberellin-regulated genes by quantitative real-time PCR（q RT-PCR）as well as signifificantly higher levels of gibberellin,suggesting that gibberellin might be partly involved in the regulation of creeping growth in lazy1.（5）The pectin and lignin contents of the lazy1 mutant were significantly higher,but the cellulose content was significantly lower.Meanwhile,q RT-PCR analysis showed the affected expression of lignin and cellulose-related genes,indicating that the metabolism related to the cell wall structure in the lazy1 mutant was interfered.（6）RNA sequencing（RNA-seq）identifified a number of differentially expressed genes（DEGs）related to gravitropism at stages I（before bending）,II（bending）,and III（after bending）between WT and lazy1.Venn diagram indicated that only Pectate lyase5 was down-expressed at stages I[Log₂fold change（Log₂FC）:-3.20],II（Log₂FC:-4.97）,and III（Log₂FC:-1.23）in lazy1,compared with WT.q RT-PCR indicated that Pectate lyas 5 was extremely down-expressed in lazy1 at stage II（0.02-fold of WT）.Gene sequencing revealed that a fragment deletion occurred in the coding region of Pectate lyase5,which induced the destruction of a pb H1 domain in Pectate lyase5 of lazy1.These results demonstrate the possibility that Pectate lyase5probably functions as the key gene that could mediate primary cell wall metabolism and get involved in the asymmetric cell elongation regulation of lazy1.