College of Life Sciences, Hebei Agricultural University, Baoding, 071001, China.
Mountainous Areas Research Institute, Hebei Agricultural University, Baoding, 071001, China.
BMC Plant Biol. 2021 Nov 3;21(1):511. doi: 10.1186/s12870-021-03280-3.
The walnut shell, which is composed of a large number of sclereids originating from the lignified parenchyma of the endocarp, plays an important role in fruit development and during harvesting and storage. The physical and chemical properties of walnut shells are closely related to the lignin content. Laccase is the key enzyme responsible for lignin biosynthesis by the polymerization of monolignols and plays crucial roles in secondary cell wall formation in plants. In this study, we screened and identified laccase family genes from the walnut genome and investigated the expression of laccase during endocarp lignification in walnut.
A total of 37 laccase genes were screened from the walnut genome and distributed on nine chromosomes and classified into 6 subfamilies, among which subfamily IV showed distinct expansion. We observed that endocarp lignification started 44 days after flowering (DAF), and at later periods, the lignin content increased rapidly, with growth peaks at 44-50 DAF and 100-115 DAF. The lignification of the endocarp proceeded from the outside to the inside, as demonstrated by section staining in combination with endocarp staining. Furthermore, the changes in the expression of laccase family genes in the endocarp at different developmental stages were studied, and JrLACs showed different expression trends. The expression of nine genes showed significant increase after 44 DAF, and among these, JrLAC12-1, JrLAC12-2 and JrLAC16 showed a significant change in expression at the lignification stage. A study of the expression of JrLACs in different tissues and at various endocarp developmental stages revealed, that most JrLACs were expressed at low levels in mature tissues and at high levels in young tissues, in particular, JrLAC12-1 showed high expression in the young stems. A significant positive correlation was found between the expression of JrLAC12-1 and the variation in the lignin content in the endocarp.
Laccase genes play an important role in the lignification of the walnut endocarp, and JrLACs play different roles during fruit development. This study shows that JrLAC12-1 may play a key role in the lignification of endocarp.
核桃壳由大量起源于内果皮木质化薄壁组织的石细胞组成，在果实发育以及收获和储存过程中起着重要作用。核桃壳的物理和化学性质与木质素含量密切相关。漆酶是通过单体酚聚合合成木质素的关键酶，在植物次生细胞壁形成中起着至关重要的作用。本研究从核桃基因组中筛选和鉴定了漆酶家族基因，并研究了核桃内果皮木质化过程中漆酶的表达。
从核桃基因组中筛选出 37 个漆酶基因，分布在 9 条染色体上，分为 6 个亚家族，其中亚家族 IV 明显扩张。我们观察到内果皮木质化始于开花后 44 天（DAF），此后木质素含量迅速增加，在 44-50 DAF 和 100-115 DAF 达到生长高峰。内果皮的木质化是从外向内进行的，这可以通过结合内果皮染色的切片染色来证明。此外，研究了不同发育阶段内果皮中漆酶家族基因的表达变化，JrLACs 表现出不同的表达趋势。在 44 DAF 后，有 9 个基因的表达显著增加，其中 JrLAC12-1、JrLAC12-2 和 JrLAC16 在木质化阶段的表达变化显著。对 JrLACs 在不同组织和不同内果皮发育阶段的表达研究表明，大多数 JrLACs 在成熟组织中表达水平较低，在幼嫩组织中表达水平较高，特别是 JrLAC12-1 在幼茎中表达水平较高。JrLAC12-1 的表达与内果皮木质素含量的变化呈显著正相关。
漆酶基因在内果皮木质化过程中起重要作用，JrLACs 在果实发育过程中发挥不同的作用。本研究表明 JrLAC12-1 可能在内果皮木质化中起关键作用。
