Loquat (Eriobotrya japonica) is a subtropical tree that bears fruit that ripens during late spring. Fruit size is one of the dominant factors inhibiting the large-scale production of this fruit crop. To date, little is known about fruit size regulation. In this study, we first discovered that cell size is more important to fruit size than cell number in loquat and that the expression of the EjBZR1 gene is negatively correlated with cell and fruit size. Virus-induced gene silencing (VIGS) of EjBZR1 led to larger cells and fruits in loquat, while its overexpression reduced cell and plant size in Arabidopsis. Moreover, both the suppression and overexpression of EjBZR1 inhibited the expression of brassinosteroid (BR) biosynthesis genes, especially that of EjCYP90A. Further experiments indicated that EjCYP90A, a cytochrome P450 gene, is a fruit growth activator, while EjBZR1 binds to the BRRE (CGTGTG) motif of the EjCYP90A promoter to repress its expression and fruit cell enlargement. Overall, our results demonstrate a possible pathway by which EjBZR1 directly targets EjCYP90A and thereby affects BR biosynthesis, which influences cell expansion and, consequently, fruit size. These findings help to elucidate the molecular functions of BZR1 in fruit growth and thus highlight a useful genetic improvement that can lead to increased crop yields by repressing gene expression.

中文翻译：

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EjBZR1 通过与枇杷中的 EjCYP90 启动子结合来抑制果实膨大

枇杷（枇杷) 是一种亚热带树，在晚春结出成熟的果实。果实大小是抑制这种水果作物大规模生产的主要因素之一。迄今为止，人们对水果大小调节知之甚少。在这项研究中，我们首次发现枇杷中细胞大小对果实大小的影响比细胞数量更重要，并且EjBZR1基因与细胞和果实大小呈负相关。病毒诱导的基因沉默（VIGS）EjBZR1导致枇杷的细胞和果实更大，而它的过度表达减少了枇杷的细胞和植物大小拟南芥. 此外，抑制和过度表达EjBZR1抑制油菜素内酯（BR）生物合成基因的表达，尤其是EjCYP90A. 进一步的实验表明EjCYP90A是一种细胞色素 P450 基因，是果实生长激活剂，而 EjBZR1 与果实的 BRRE (CGTGTG) 基序结合EjCYP90A启动子抑制其表达和果实细胞增大。总的来说，我们的结果证明了 EjBZR1 直接靶向的可能途径EjCYP90A从而影响 BR 的生物合成，从而影响细胞的扩张，从而影响果实的大小。这些发现有助于阐明 BZR1 在果实生长中的分子功能，从而突出一种有用的遗传改良，它可以通过抑制基因表达来提高作物产量。