Physiological Function Analysis Of NAL1 Gene Affecting Sink-source In Rice

The yield of rice mainly determined by the source,sink and flow as well as the degree of therir coordination.However,little has been reported on the physiological mechanism of genes controlling sink,source and flow traits in rice.In our previous studies,we isolated and cloned a gene NAL1 consistently influencing sink（eg.,grain number per panicle）and source（e.g.,flag leaf size）related traits in rice through map-based cloning.A near-isogenic line,NIL-NAL1^LT,was developed in Teqing genetic background,which only differed in～50.5 kb region containing NAL1 derived from Lemont by marker-assisted introgression.In this study,NIL-NAL1^LTand its recurrent parent Teqing were used as test materials to analyze the physiological functions of NAL1 influencing sink,source and flow related traits in rice.1.Compared with Teqing,NIL-NAL1^LTsignificantly increased the number of secondary branches,filled grain number per panicle and total spikelet number per panicle,slightly increased 1000-grain weight,and slightly decreased but no significantly differences in the effective panicle number.Finally,the NIL-NAL1^LTproduced averagely 5.5%higher grain yield across the three environments,indicating that the NAL1^LTallele can potentially be used in high yield rice breeding.2.Compared with Teqing,NIL-NAL1^LTimproved appearance quality,processing quality and eating quality,as indicated that degree of endosperm chalkiness,and percentage of grains with chalkiness were significantly decreased,milled rice rate and head milled rice rate were significantly increased,amylose content and protein content were significantly decreased,taste and palatability value was significantly increased.The improved quality of NIL-NAL1^LTmight be attributed to the significant improvement of grain filling,especially the grain filling of inferior spikelets.3.Compared with Teqing,NIL-NAL1^LTshowed significantly larger lengths,widths and areas of flag and second leaves and leaf area index at the full heading stage.However,NIL-NAL1^LTexhibited slightly decreased but no significantly difference in the net photosynthetic rate of flag leaves after heading.At the full heading stage,the non-structural carbohydrate content of NIL-NAL1^LTwas significantly higher than that of Teqing.According to the above results,we concluded that NIL-NAL1^LThad relatively abundant source supply which could fully meet the increased sink capacity.4.During the whole grain filling process,the grain weight and starch content of NIL-NAL1^LTfor both superior spikelets（SS）and spikelets（IS）were much higher than those of Teqing,and its higher grain weight of IS was more aggravated.At maturity stage,the grain weight of NIL-NAL1^LTfor SS and IS were 2.4%and 47.9%higher than that of Teqing,respectively.The significantly increased grain weight of NIL-NAL1^LTfor IS was mainly attributed to grain size,grain bulk density and grain filling improvement.5.NIL-NAL1^LTsignificantly increased the number of large vascular bundles in panicle neck,and phloem area of vascular bundles in panicle neck,rachis branches and flag leaves.In addition,the apparent transferred mass of non-structural carbohydrates in stems and sheaths from stems to grains in NIL-NAL1^LTwas significantly increased compared with Teqing,indicating that NIL-NAL1^LTexhibited greater vascular system contributing to photoassimilates transport to spikelets.6.NIL-NAL1^LTcould enhance grain yield and quality via coordinated source-sink-flow relation.This study elucidated the physiological functions of NAL1 gene in regulating source,sink,and flow in rice.The results The results had important guiding significance for further breeding of rice super high yield cultivars with source-sink harmony by molecular design breeding technology.