| Rice is the major food crop.With the rapid increase of the world’s population,it is necessary to continuously increase food production to meet the growing food demand.Rice architecture refers to a set of characteristics related to crop yield,which mainly determined by plant height,number of tillers,and inflorescence morphology,tiller angle and leaf angle.DDM1 is a chromatin remodeling factor of the SWI2/SNF2 family,which can maintain DNA methylation and play an important role in gene regulating gene expression.We mainly study the effects of DDM1 on gene DNA methylation and gene expression,its molecular mechanism regulating rice architecture.1.DDM1 mutation can activate genes and transposons expressionPrevious studies have shown that rice DDM1 mutation result in great loss of genomic DNA methylation and activating of large number of genes.Further analysis revealed that 2710（93.00%）,179（6.14%）,and 25（0.86%）of ddm1a/1b up-regulated genes,which showed low-,medium-,and high-expression separately in WT.The proportions TE-related genes were 64.1%,13.4%,and 0%separately.This indicates that DDM1 maintain DNA methylation to repress genes and TEs expression,and regulate rice architecture.2.DDM1 mutation results in increasing of leaf angleWe found that the inverted three and four leaf angles of the 45-day-old ddm1a/1b mutant increased by 337.18%and 113.70%relative to the wild type.The sensitivity of the second leaf angle of the 12d ddm1a/1b mutant of BL treatment increased.We analyzed genome-wide DNA methylation data,transcription data and RT-qPCR data of the mutants,and found that the methylation of the promoter regions of BR biosynthesis genes and BR signal pathway positive regulators encode gene decreased and their expression increased3.DDM1 mutation affects rice panicle and anther developmentWe performed phenotypic statistics and found that the panicle length of mature ddm1a/1b mutant was just half the length of the wild type.The number of primary branch and spikelet were significantly reduced,and there were almost no secondary branch stalks.The mutant was completely infertile.We analyzed the expression of CKX（cytokinin oxidase）family genes in ddmla/1b mutant and wild type,and found that the expression levels of OsCKX3,OsCKX4,OsCKX5,and OsCKX8 were significantly increased,and the expression level of OsCKX11 was decreased.RT-qPCR data showed that the expression of OsCKXs in the wild type decreased with panicle development and the expression of OsCKX2,OsCKX4,OsCKX7 and OsCKX9 in panicle of ddm1a/1b mutant were significantly increased We found the methylation of OsCKX2,OsCKX4,OsCKX7,OsCKX8 and OsCKX9 promoter reduced on CG,CHG and CHH sequence depend on genome-wide DNA methylation data.Our previous studies found that ddm1a/1b mutant couldn’t form mature pollen,which leading to male sterility.But the ovaries of the ddm1a/1b mutant expanded to the similar size as wild-type ovaries after anthesis,produced parthenocarpic seeds filled with a sucrose-rich liquid,but no starch accumulation was detected.We performed paraffin section of rice anthers and found that the tapetum degradation of the ddm1a/1b mutant was degraded during mitosis.Anthers chambers at mature stage still had an undegraded tapetum,and the microspore development was delayed and they could not form mature pollen.RT-qPCR data showed that the expression of genes EAT1,CP1,AP37 and API5 related to PCD in tapetum were decreased.In addition,a large number of paraffin sections showed that mutant anthers always have 1-2 anther chambers that development abnormal.This study shows that rice DDM1 plays an important role in maintaining DNA methylation of the genome and inhibiting the expression of transposons and genes.DDM1 mutation causes changes in the expression of BR-related genes in rice and affects leaf angle development;affects the expression of CKX family genes resulting in abnormal development of rice spikelets;also affects the expression of genes related to anther development,leading to delayed tapetum degradation result in male sterility. |
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