Genomewide analysis of the lateral organ boundaries domain gene family in Eucalyptus grandis reveals members that differentially impact secondary growth

Abstract

SummaryLateral Organ Boundaries Domain (LBD) proteins are plant‐specific transcription factors playing crucial roles in growth and development. However, the function of LBD proteins in Eucalyptus grandis remains largely unexplored. In this study, LBD genes in E. grandis were identified and characterized using bioinformatics approaches. Gene expression patterns in various tissues and the transcriptional responses of EgLBDs to exogenous hormones were determined by qRT‐PCR. Functions of the selected EgLBDs were studied by ectopically overexpressing in a hybrid poplar (Populus alba × Populus glandulosa). Expression levels of genes in the transgenic plants were investigated by RNA‐seq. Our results showed that there were forty‐six EgLBD members in the E. grandis genome and three EgLBDs displayed xylem‐ (EgLBD29) or phloem‐preferential expression (EgLBD22 and EgLBD37). Confocal microscopy indicated that EgLBD22, EgLBD 29 and EgLBD37 were localized to the nucleus. Furthermore, we found that EgLBD22, EgLBD29 and EgLBD37 were responsive to the treatments of indol‐3‐acetic acid and gibberellic acid. More importantly, we demonstrated EgLBDs exerted different influences on secondary growth. Namely, 35S::EgLBD37 led to significantly increased secondary xylem, 35S::EgLBD29 led to greatly increased phloem fibre production, and 35S::EgLBD22 showed no obvious effects. We revealed that key genes related to gibberellin, ethylene and auxin signalling pathway as well as cell expansion were significantly up‐ or down‐regulated in transgenic plants. Our new findings suggest that LBD genes in E. grandis play important roles in secondary growth. This provides new mechanisms to increase wood or fibre production.

Phylogeny and Functions of LOB Domain Proteins in Plants

“…LBD genes were identified from many genome-available plant species, including Arabidopsis [2], rice [36], poplar [37], tomato [27], Malus domestica (apple) [28], Medicago truncatula [29], maize [30], grape [31], mulberry [32], barley [33], Camellia sinensis [34] and Eucalyptus grandis [35], with gene…”

“…LBD genes were identified from many genome-available plant species, including Arabidopsis [2], rice [36], poplar [37], tomato [27], Malus domestica (apple) [28], Medicago truncatula [29], maize [30], grape [31], mulberry [32], barley [33], Camellia sinensis [34] and Eucalyptus grandis [35], with gene family sizes ranging from 24 to 58 genes. Recently, several studies focused on LBD protein identification and their novel roles are reported [26,[50][51][52][53].…”

Genome-Wide Analysis of the Lateral Organ Boundaries Domain Gene Family in Brassica Napus

“…WGD/segmental duplication is very common in plant genomes, as most plants have undergone polyploidy events during evolution, and thus retain many duplicated chromosome segments in their genomes [50,51]. Compared with other plant species such as Arabidopsis, O. sativa, Z. mays, G. max, and Populus, which contain 43,35,44,80, and 57 LBD genes [1,6,12,13], respectively, we found B. napus with the largest number of LBD genes, indicating the genome duplication during evolution of B. napus greatly contributed to the diversification of BnLBDs. Further, all 126 BnLBD genes were identified as the result of gene duplication, 93 of them were identified with WGD or segmental duplications history, and the rest resulted from dispersed duplications.…”

“…Following the identification of LBD genes in Arabidopsis, LBDs have been found in other plant species, such as Oryza sativa, Malus domestica, Zea mays, Vitis vinifera, Morus notabilis, Lotus japonicas, Medicago truncatula, Brachypodium distachyon, Glycine max, and Eucalyptus grandis. The number of LBD members ranged from 28 to 90 in different plants [4][5][6][7][8][9][10][11][12][13]. However, LBDs have never been identified in any species other than plants, indicating that LBD is a plant-specific gene family [1].…”

Comparative transcriptome profiling provides insights into endocarp lignification of walnut (Juglans Regia L.)

“…The positive feedback regulation network formed by LBD and NAC protein regulates the secondary growth of Arabidopsis by controlling the differentiation of xylem cells [63]. The LBD family has several biological functions such as plant development, secondary growth, pathogen response, biological stress and hormone signaling [64][65][66][67][68]. LBD25 can control the growth of the hypocotyl of Arabidopsis by regulating the morphogenesis of light, resulting in the failure of the hypocotyl of LBD25 mutant under dark culture conditions [69].…”