Cloning and functional verification of rate-limiting enzyme FaYUC11 in strawberry auxin biosynthesis

Abstract：【Objective】Cloning and functional verification of a new crucial regulator gene in strawberry auxin biosynthesis.【Methods】The FaYUC11 for fruit enlargement was isolated from the‘Jiuxiang'cultivated strawberry (Fragaria×ananassa ‘Jiuxiang') by using RT-PCR (reverse transcription PCR) , and then the function of FaYUC11 in strawberry fruit was analyzed by VIGS (virus-induced gene silencing) technology to complete our investigation. The total RNA of the strawberry fruit was extracted by CTAB (Hexadecyl trimethyl ammonium Bromide) . Specific primers were designed according to the homologous gene sequences of F. vesca for PCR amplification. After the PCR products were verified by sequencing, they were then compared with the YUC gene family members, and according to the comparison results, specific areas were selected close to the 5'end of FaYUC11 to design the interference primers, using the plasmid with FaYUC11 full-sequence as the template for amplification. Then the products were integrated into the virus RNA plasmid p TRV2, in order to obtain a p TRV2-d YUC11 virus induced gene silencing carrier. The infection vector p TRV2-d YUC11 was constructed and transformed into the Agrobacterium strain GV3101. The resultant Agrobacterium was microinjected into the strawberry fruit to induce gene silencing. 34 days after infection, an analysis was done of each index of the virus induced gene silencing strawberries. The expression of FaYUC11 was analyzed using q RT-PCR (Quantita-tive Real-time PCR) , the content of the free IAA in the strawberry achenes (seeds) was detected by GCMS, and the phenotypic changes of the strawberry fruits infected by p TRV2-YUC11 were analyzed, and then compared with the percentage increase of the longitudinal and traverse diameters of the strawberry fruits.【Results】Compared with wild type strawberry fruits, the expression of fruits with the treatment of the p TRV2 empty vector was 1.13, while the expression of fruits with the p TRV2-YUC11 infection were 0.18 and 0.44. The results of q RT-PCR showed that, the FaYUC11 decreased in transcript accumulation levels with different degrees in the strawberry fruits infected with p TRV2-YUC11. The content of the free IAA in the strawberry achenes (seeds) was detected by GC-MS, the results showed that, compared with the group that were treated with the p TRV2 empty vector (515.2 ng·g^-1) , it significantly decreased in the fruits infected by p TRV2-YUC11 (64.86 ng·g^-1, 307.19 ng·g^-1) , which indicated that FaYUC11 is a significant regulator for IAA accumulation. Phenotypic change analysis of the strawberry fruits at 34 days after infection showed that there were mildly sunken at the top of the fruits that were treated with p TRV2 empty vector, but it did not affect fruit enlargement and its morphology, while the fruits infected by p TRV2-YUC11 were significantly suppressed, with some of the fruits enlargement of inhibition being minor (Ri YUC11-3) , but part of the fruits were severely inhibited (Ri YUC11-2) , with little change showing after 34 days growth, with some still being in the small green fruit stage. Furthermore, by analyzing the percentage increase of longitudinal and traverse diameters of the strawberry fruits found, compared with the wild type fruits, there was a significant decrease in the fruits infected by p TRV2-YUC11. This indicates that FaYUC11 regulates the increase of longitudinal and traverse diameters of strawberry fruits.【Conclusion】The lack of FaYUC11 led to free IAA content in strawberry achenes (seeds) and the percentage increase of the longitudinal and traverse diameters of strawberry fruits were reduced, and at the same time, this influenced the fruit enlargement and normal growth. It indicated that FaYUC11 plays a significantly important role in the regulation of strawberry fruit size. This provides good application prospects in the regulatory functions of strawberry fruit size and has great significance in the development of molecular markers for functional SNP and large strawberry fruit breeding.