NOVELTY - An isolated polypeptide having beta-xylosidase activity is new.    USE - The polypeptide is useful for degrading or converting or fermenting a cellulosic or xylan-containing material, and for producing a fermentation product (all claimed), and for saccharifying the cellulosic or xylan-containing material to fermentable sugars and to convert the fermentable sugars to useful fermentation products, e.g., fuel, potable ethanol, and/or platform chemicals (e.g., acids, alcohols, ketones, gases, and the like).    ADVANTAGE - Improved cellulolytic enzyme compositions with increased efficiency and which provides cost-effective enzyme solutions for degradation of lignocellulose are provided.    DETAILED DESCRIPTION - An isolated polypeptide having beta-xylosidase activity is selected from (i) a polypeptide having at least 60% sequence identity to the mature polypeptide of SEQ ID NO: 6 or SEQ ID NO: 8; at least 65% sequence identity to the mature polypeptide of SEQ ID NO: 2; or at least 75% sequence identity to the mature polypeptide of SEQ ID NO: 4 or SEQ ID NO: 10; (ii) a polypeptide encoded by a polynucleotide that hybridizes under at least medium-high stringency conditions with (i) the mature polypeptide coding sequence of SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, or SEQ ID NO: 9, (ii) the cDNA sequence of SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, or SEQ ID NO: 7, or (iii) the full-length complement of (i) or (ii); (iii) a polypeptide encoded by a polynucleotide having at least 60% sequence identity to the mature polypeptide coding sequence of SEQ ID NO: 5 or SEQ ID NO: 7, or their cDNA sequences; at least 65% sequence identity to the mature polypeptide coding sequence of SEQ ID NO: 1 or its cDNA sequence; or at least 75% sequence identity to the mature polypeptide coding sequence of SEQ ID NO: 3 or its cDNA sequence or SEQ ID NO: 9; (iv) a variant of the mature polypeptide of SEQ ID NO: 2, SEQ ID NO: 4, SEQ ID NO: 6, SEQ ID NO: 8, or SEQ ID NO: 10 comprising a substitution, deletion, and/or insertion at one or more positions; and (v) a fragment of the polypeptide of (i), (ii), (iii), or (iv) that has beta-xylosidase activity. Sequences not defined here may be found at ftp://ftp.wipo.int/pub/published_pct_sequences/publication. INDEPENDENT CLAIMS are:    (1) an isolated polynucleotide encoding the polypeptide above;    (2) a recombinant host cell comprising the polynucleotide of (1) operably linked to one or more control sequences that direct the production of the polypeptide;    (3) a method of producing the polypeptide above;    (4) a transgenic plant, plant part or plant cell transformed with a polynucleotide encoding the polypeptide above;    (5) a method of producing a mutant of a parent cell by inactivating a polynucleotide encoding the polypeptide above, which results in the mutant producing less of the polypeptide than the parent cell;    (6) a double-stranded inhibitory RNA (dsRNA) molecule comprising a subsequence of the polynucleotide of (1), where optionally the dsRNA is a small interfering RNA (siRNA) or a microRNA (miRNA) molecule;    (7) a method of inhibiting the expression of a polypeptide having beta-xylosidase activity in a cell by administering to the cell or expressing in the cell the dsRNA molecule of (6);    (8) an isolated polynucleotide encoding a signal peptide comprising or consisting of amino acids 1 to 19 of SEQ ID NO: 2, amino acids 1 to 19 of SEQ ID NO: 4, amino acids 1 to 19 of SEQ ID NO: 6, amino acids 1 to 21 of SEQ ID NO: 8, or amino acids 1 to 20 of SEQ ID NO: 10;    (9) a process for degrading or converting a cellulosic or xylan-containing material by treating the cellulosic or xylan-containing material with an enzyme composition in the presence of the polypeptide having beta-xylosidase activity above;    (10) a process for producing a fermentation product by (a) saccharifying a cellulosic or xylan-containing material with an enzyme composition in the presence of the polypeptide having beta-xylosidase activity above; (b) fermenting the saccharified cellulosic or xylan-containing material with one or more fermenting microorganisms to produce the fermentation product; and (c) recovering the fermentation product from the fermentation;    (11) a process of fermenting a cellulosic or xylan-containing material by fermenting the cellulosic or xylan-containing material with one or more fermenting microorganisms, where the cellulosic or xylan-containing material is saccharified with an enzyme composition in the presence of the polypeptide having beta-xylosidase activity above; and    (12) a whole broth formulation or cell culture composition comprising the polypeptide above.