BcMF26a and BcMF26b Are Duplicated Polygalacturonase Genes with Divergent Expression Patterns and Functions in Pollen Development and Pollen Tube Formation in Brassica campestris

Abstract

Polygalacturonase (PG) is one of the cell wall hydrolytic enzymes involving in pectin degradation. A comparison of two highly conserved duplicated PG genes, namely, Brassica campestris Male Fertility 26a (BcMF26a) and BcMF26b, revealed the different features of their expression patterns and functions. We found that these two genes were orthologous genes of At4g33440, and they originated from a chromosomal segmental duplication. Although structurally similar, their regulatory and intron sequences largely diverged. QRT-PCR analysis showed that the expression level of BcMF26b was higher than that of BcMF26a in almost all the tested organs and tissues in Brassica campestris. Promoter activity analysis showed that, at reproductive development stages, BcMF26b promoter was active in tapetum, pollen grains, and pistils, whereas BcMF26a promoter was only active in pistils. In the subcellular localization experiment, BcMF26a and BcMF26b proteins could be localized to the cell wall. When the two genes were co-inhibited, pollen intine was formed abnormally and pollen tubes could not grow or stretch. Moreover, the knockout mutants of At4g33440 delayed the growth of pollen tubes. Therefore, BcMF26a/b can participate in the construction of pollen wall by modulating intine information and BcMF26b may play a major role in co-inhibiting transformed plants.

Patterns of Expansion and Expression Divergence of the Polygalacturonase Gene Family in Brassica oleracea

“…At the transcription level, the combination of cis-acting elements and transcription factors in the promoter region is involved in the regulation of gene expression. For example, two duplicated PG genes, BcMF26a and BcMF26b , in B. rapa , with amino acid sequences, had 92.19% similarity and showed a divergent expression and function, which may be responsible for their promoters having a very large divergence (63.20% similarity) [ 44 ]. In our study, the cis-elements in BoPGs’ promoter sequences were identified and analyzed.…”

The Arabidopsis COPII components, AtSEC23A and AtSEC23D, are essential for pollen wall development and exine patterning

“…Possibly, the thickened intine in atsec23a is responsible for the impaired pollen germination rate by increasing the required pressure for pollen germination. In Brassica campestris , knockdown of BcMF8 (putative arabinogalactan protein gene) and double knockdown of BcMF26a and BcMF26b (polygalacturonase genes) causes reduced pollen germination and retarded pollen tube growth as a result of remarkable thickening of the intine ( Lin et al , 2014 ; Lyu et al , 2015 ). In atsec23a , AtSEC23D had the main function in pollen development.…”

A Global Analysis of the Polygalacturonase Gene Family in Soybean (Glycine max)

“…PG is one of the major enzymes involved in pectin disassembly by biochemically catalyzing the hydrolytic cleavage of a (1–4) galacturonan [ 37 – 38 ]. Pectin is one of the major components of the primary cell wall, whose disassembling leads to cell wall separation [ 39 – 40 ].…”