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Abstract
Pectin is a major component of plant cell walls, and the structure of pectin impacts on the properties of wood. Although we know that pectate lyase (PL, EC 4.2.2.2) has a major influence on the structure of pectin, our knowledge of Pectate lyase-like genes (PLL) in tree species remains limited. To better understand the characteristics of PLL genes in trees and to identify novel PLL genes that are potentially involved in the development of wood, we performed comprehensive analyses of gene structures, phylogenetic relationships, chromosomal locations, gene duplication events, conserved protein motifs, and gene expression patterns of 30 PLLs in Populus trichocarpa (PtPL1s). We performed an in silico gene expression profiling and quantitative real-time PCR analysis and found that most of the PtPL1 genes from subgroups Ia and Ib were highly expressed in xylem. PtPL1-18 from subgroup Ia was preferentially expressed in developing primary xylem and in xylem cells that were developing secondary walls. Overexpression of PtPL1-18 in poplar reduced plant growth and xylem development. Reduced secondary cell wall thickening and irregular xylem cells were observed in the transgenic trees, probably due to their lower pectin content. Although pectin is not a major component of plant secondary cell walls, our results are consistent with the PtPL1 genes performing important functions during wood formation.
Highlights
Populus is a genus of trees among the most important boreal broadleaf trees, for its plentiful and renewable supplies of wood in pulping, construction, and energy industries
Twentyeight of them have been previously identified in the first version of Populus genome, named as PtPL1-1 to PtPL1-28 (Geisler-Lee et al, 2006); and one member was identified in the Populus assembly v2.2, named as PtPL1-29 (Biswal et al, 2014)
Despite its low abundance in the secondary cell walls, recent researches have implied that pectin influences secondary wall formation in addition to its roles in primary wall biosynthesis and modification
Summary
Populus is a genus of trees among the most important boreal broadleaf trees, for its plentiful and renewable supplies of wood in pulping, construction, and energy industries. Formation of wood is a sequential developmental process, including vascular cambial division, differentiation of secondary xylem mother cells, cell expansion, massive deposition of secondary walls, programmed cell death, and formation of heartwood (Plomion et al, 2001). PtPL1-18 in Poplar Vascular Development secondary cell wall is essential for wood development and has been comprehensively studied, with focus on cellulose, hemicellulose, and lignin, the three main compositions of wood (Ye and Zhong, 2015). The study of relation between pectin and secondary wall was limited. It is known that pectin mainly exists in the primary cell wall and the middle lamella of plants
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