Functional Study On Overexpression Of OsPIN9 In Rice Development

As the most important hormone in plants,auxin(IAA)is involved in regulating the formation and development of various morphological organs.IAA polar transportation relies on polar transportation input and output carriers to complete.OsPIN9 is a unique IAA polar transport output vector in monocotyledonous plants.It does not have homologous genes with arabidopsis and does not have multiple homologous genes like other Os PINs.Previous research on OsPIN9 has been relatively limited.In order to explore the role of OsPIN9 gene in rice growth and development,this study used transgenic rice OE1 and OE2 overexpressing OsPIN9 and wild-type Zhonghua 11(WT)as materials.Compare the differences in Os PINs gene expression,seed germination rate,and copper stress tolerance among WT,OE1 and OE2 rice varieties.Clarify the phenotypic differences in WT,OE1 and OE2 rice at different growth stages,and further determine the reasons for the phenotypic differences through physiological measurements.To elucidate the mechanism of action of OsPIN9 at different stages of rice growth.The results showed that:(1)Overexpression of OsPIN9 promoted the expression of Os PIN1 s and Os PIN2 genes at different developmental stages of rice,indicating a possible synergistic effect between Os PIN1 s and Os PIN2 with OsPIN9.(2)Promote IAA polar transport,thereby increasing amylase activity during seed germination.Starch decomposition provides sufficient nutrients for rice seed germination,promoting rapid germination of rice seeds.(3)Increasing the height of rice plants promotes an increase in leaf width and length,resulting in more developed microtubule tissue and an increase in the number of vascular bundles in the leaves.During the booting stage,the plant height of OE1 and OE2 was 17.40% and 23.90% higher than that of WT,the flag leaf length was21.26% and 41.26% longer than that of WT,the flag leaf width was 18.05% and22.56% wider than that of WT,and the leaf area increased by 43.14% and83.74%,respectively.At the same time,the expression levels of water channel protein genes Os PIP1-2,Os PIP2-4,Os PIP2-7,Os PIP2-8,Os TIP1-1,Os TIP2-2and Os TIP4-1 in flag leaves were significantly higher than those in WT,promoting water transport and photosynthesis in rice leaves.During the flowering period,the net photosynthetic rates of flag leaves in OE1 and OE2 increased by 14.61% and 27.66% respectively compared to WT,and the transpiration rates increased by 11.27% and 22.39% respectively.The stomatal conductance increased by 14.81% and 29.63% respectively compared to WT.The increase in photosynthetic rate is beneficial for the accumulation of photosynthetic products,thereby promoting the plumpness of rice grains and increasing rice yield.For example,OE2 increased the number of grains per panicle by 46.57% compared to WT,seed width by 7.70% compared to WT,grain length by 11.86% compared to WT,and thousand grain weight by 37.91%compared to WT.(4)After overexpression of OsPIN9,the contents of active auxin,GA(Gibberellins)and CTK(Cytokinin)in rice roots and leaves were significantly increased.GA promoted cell elongation and growth,and CTK promoted cell division,thus increasing plant height,leaf length and leaf width of OE1 and OE2.(5)Under copper stress,OE1 and OE2 rice overexpressing OsPIN9 showed significantly lower growth inhibition than WT,and both exhibited higher antioxidant enzyme activity,demonstrating stronger copper stress tolerance than WT.Therefore,overexpression of OsPIN9 accelerates the polar transport of IAA,and there is a synergistic effect between Os PINs genes.The plant height,leaf length,leaf width,and number of leaf veins increase,the vascular bundles become more developed,the chlorophyll content and photosynthetic rate increase,thereby promoting grain filling,increasing the length and number of rice panicles,and achieving an increase in yield.In addition,overexpression of OsPIN9 improved the tolerance of rice under copper stress.This is of great significance for selecting better rice varieties,indicating that the OsPIN9 gene has great application prospects in high-yield rice breeding.