Abstract
The accumulation of lignin in fruit has a significant negative impact on the quality of fruit-producing trees, and in particular the lignin formation stimulates the development of stone cells in pear fruit. Reactive oxygen species (ROS) are essential for lignin polymerization. However, knowledge of the RBOH family, a key enzyme in ROS metabolism, remains unknown in most fruit trees. In this study, a total of 40 RBOHs were identified from five fruit-producing trees (Pyrus bretschneideri, Prunus persica, Citrus sinensis, Vitis vinifera, and Prunus mume), and 10 of these sequences came from Pyrus bretschneideri. Multiple sequence alignments revealed that all 10 PbRBOHs contained the NADPH_Ox domain and the six alpha-helical transmembrane domains (TM-I to TM-VI). Chromosome localization and interspecies phylogenetic tree analysis showed that 10 PbRBOHs irregularly distributed on 8 chromosomes and 3 PbRBOHs (PbRBOHA, PbRBOHB, and PbRBOHD) are closely related to known lignification-related RBOHs. Furthermore, hormone response pattern analysis showed that the transcription of PbRBOHs is regulated by SA, ABA and MeJA. Reverse transcription-quantitative real-time polymerase chain reaction (qRT-PCR) and transcriptome sequencing analysis showed that PbRBOHA, PbRBOHB, and PbRBOHD accumulated high transcript abundance in pear fruit, and the transcriptional trends of PbRBOHA and PbRBOHD was consistent with the change of stone cell content during fruit development. In addition, subcellular localization revealed that PbRBOHA and PbRBOHD are distributed on the plasma membrane. Combining the changes of apoplastic superoxide (O2.−) content and spatio-temporal expression analysis, these results indicate that PbRBOHA and PbRBOHD, which are candidate genes, may play an important role in ROS metabolism during the lignification of pear stone cells. This study not only provided insight into the molecular characteristics of the RBOH family in fruit-producing trees, but also lays the foundation for studying the role of ROS in plant lignification.
Highlights
Pyrus spp. is one of the world’s most important deciduous fruit trees
We found that 70% of the PbRBOH family members have ABRE (ABA-responsive) in their promoters and 50% of members contain TGACG-motif (MeJA-responsive)
We identified 10, 7, 8, 8 and 7 members of the respiratory burst oxidase homolog (RBOH) family from the pear, peach, mei, sweet orange and grape genomes, respectively
Summary
Pyrus spp. is one of the world’s most important deciduous fruit trees. Asiatic pears or Oriental pears are mainly distributed in East Asia, and the main cultivars include P. bretschneideri, P. sinkiangensis, P. sinkiangensis, P. ussuriensis and P. pyrifolia [1,2,3]. ‘Dangshan Su’ has the defect of a high content of large-diameter stone cell cluster in the fruit, which seriously affects its quality and economic value [4,5,6]. The large diameter and high content of stone cell clusters are the “common problems” of some P. ussuriensis and P. pyrifolia varieties [1]. Reducing the size and content of the stone cell cluster of pear fruit and improving the fruit quality is an urgent problem to be solved in the pear industry
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